JP5221268B2 - Power switching element driving circuit, driving method thereof, and switching power supply device - Google Patents

Description

  The present invention relates to a drive circuit that outputs a drive signal of a power switching element in a switching power supply device.

  In recent years, from the standpoint of measures to prevent global warming, attention has been focused on reducing standby power consumption of home appliances and the like, and a switching power supply device with lower power consumption during standby is strongly demanded.

  FIG. 19 is a diagram illustrating an example of the configuration of the switching power supply device. The switching power supply apparatus 200 outputs a stable DC voltage by controlling on / off of the voltage-controlled switching element 25. Specifically, the switching power supply apparatus 200 includes a primary side rectifying / smoothing circuit 101, a switching circuit 102, a transformer 103, a secondary side rectifying / smoothing circuit 104, and a feedback circuit 119.

  The primary-side rectifying / smoothing circuit 101 includes a diode bridge 109 and an input capacitor 110, and the voltage that has been full-wave rectified by the diode bridge 109 is smoothed by the input capacitor 110.

  The switching circuit 102 switches the voltage-controlled switching element at high speed and outputs high-frequency alternating current to the transformer 103. Specifically, the switching circuit 102 includes an external resistor 121 of the driving circuit, a resonance capacitor 122, a driving circuit 108, and a voltage control type switching element 25. The voltage controlled switching element 25 is a power switching element such as a MOSFET.

  A primary winding 111 is provided in the transformer 103. The primary winding 111 and the voltage-controlled switching element 25 are connected in series, and an input DC voltage is supplied to the series connection circuit.

  The gate terminal of the voltage-controlled switching element 25 is connected to the drive circuit 108, and conduction and interruption are controlled by a drive signal output from the drive circuit 108.

  In the transformer 103, a secondary winding 112 magnetically coupled to the primary winding 111 and an auxiliary winding 120 magnetically coupled to the primary winding 111 and the secondary winding 112 are provided. When the voltage control type switching element 25 performs a switching operation and a current flows intermittently in the primary winding 111, a voltage is induced in the secondary winding 112 and the auxiliary winding 120.

  The secondary side rectifying / smoothing circuit 104 rectifies and smoothes the voltage induced in the secondary winding 112 to generate a DC output voltage, and outputs it from the output terminal 117 and the output terminal 118. Here, the secondary side rectifying / smoothing circuit 104 includes a rectifying diode 113, a choke coil 114, a first output capacitor 115, and a second output capacitor 116. The choke coil 114, the first output capacitor 115, and the second output capacitor 116 are π-type connected, and the voltage induced in the secondary winding 112 is half-wave rectified by the rectifier diode 113, and the choke Smoothing is performed by the coil 114, the first output capacitor 115, and the second output capacitor 116.

  The voltage generated at both ends of the auxiliary winding 120 is input to the control terminal of the voltage-controlled switching element 25 through the drive circuit 108. The switching power supply device 200 is a ringing choke converter (hereinafter referred to as RCC) system, and the voltage control type switching element 25 performs a switching operation by self-excitation by a voltage generated in the auxiliary winding 120.

  Inside the drive circuit 108, a voltage induced in the auxiliary winding 120 is used to generate an auxiliary DC voltage, and the drive circuit 108 operates with the auxiliary DC voltage except during starting.

  At the time of start-up, that is, when an AC voltage is applied between the input terminals 105 and 106, the voltage-controlled switching element 25 is not performing a switching operation. The circuit 108 is in a non-powered state. Therefore, in order to start switching, a low voltage suitable for starting the drive circuit 108 is supplied from the primary side rectifying / smoothing circuit 101 through the external resistor 121 (high withstand voltage, high power) of the drive circuit.

  The voltage value or current value between the output terminal 117 and the output terminal 118 is fed back to the drive circuit 108 via the feedback circuit 119. For example, when the voltage between the output terminal 117 and the output terminal 118 decreases, the drive circuit 108 forcibly lengthens the conduction period of the voltage-controlled switching element 25, and conversely, the output terminal 117 and the output terminal When the voltage with respect to 118 increases, the conduction period of the switching element 107 is forcibly shortened so that the voltage appearing between the output terminals 117 and 118 is maintained at a constant value.

  Here, in the above-described RCC switching power supply device 200, when the load connected between the output terminals 117 and 118 is heavy, the conduction period of the voltage-controlled switching element 25 becomes long, and the primary winding 111 When a large current flows, the voltage between the output terminals is maintained at a constant value. Conversely, during a light load such as a standby state, the conduction period of the voltage-controlled switching element 25 is shortened, and the current flowing through the primary winding 111 is reduced, so that the voltage between the output terminal 117 and the output terminal 118 becomes a constant value. Maintained. In the RCC method, the switching frequency increases as the conduction period of the voltage-controlled switching element 25 decreases.

  FIG. 20 is a timing chart showing the power supply output current Io and output voltage Vo of the conventional switching power supply apparatus 200 and the drain current and gate voltage of the voltage-controlled switching element 25 for different load states. As described above, the drain current of the voltage-controlled switching element 25 changes according to the load connected between the output terminals 117 and 118. Hereinafter, in this specification, the drain current flowing through the voltage-controlled switching element 25 is defined as a load current.

  The rated load state is, for example, a state in which the television is turned on, and is a state in which the most current flows in the normal operation range. In addition, the standby state is a state in which the television is turned off and the load waiting for remote control operation is light, for example, and the load fluctuation state is a state of a transition period from the rated load state to the standby state.

  In the rated load state, a large amount of power supply output current Io that is a current output from the switching power supply apparatus 200 flows, so that the power supply output voltage Vo that is a voltage between the output terminal 117 and the output terminal 118 is low. When Vo is low, the drive circuit 108 increases the drain width Ids flowing through the voltage controlled switching element 25 by increasing the pulse width of the gate voltage Vgs of the voltage controlled switching element 25.

  Next, in the load fluctuation state, since the load is gradually lightened, the power supply output current Io decreases, and the power supply output voltage Vo increases accordingly. When Vo rises, the drive circuit 108 suppresses the drain current Ids by gradually narrowing the pulse width of the gate voltage Vgs.

  In the standby state, the power output current Io further decreases and the power output voltage Vo increases. When Vo is high, the pulse width of the gate voltage Vgs is further narrowed, and the drain current Id is further suppressed.

  In the switching power supply device 200 as described above, power loss mainly occurs in the voltage controlled switching element 25. The voltage controlled switching element 25 is usually a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor). In general, a bipolar transistor has a large switching loss when switching from a conductive state to a cut-off state, but a MOSFET has a small switching loss because of its high switching speed. On the other hand, unlike a bipolar transistor, a MOSFET has a large conduction resistance, so conduction loss cannot be ignored. Therefore, the loss increases when a large current flows. Therefore, the gate voltage of the MOFSFET is set high, the conduction resistance is lowered, and the conduction loss is reduced.

Also, in recent years, it is operated as a MOSFET that is advantageous for high frequency and low current at a light load such as standby mode, and on the other hand, an IGBT (Insulated Gate Bipolar Transistor) operation that is advantageous for low frequency and large current is performed at a heavy load. A device that selectively uses two types of operations has also been proposed (see, for example, Patent Document 1). In this device, when a large current flows, the conduction resistance can be further reduced by the bipolar operation by the IGBT operation, so that it is possible to comprehensively reduce both the switching loss and the conduction loss over the entire region from the light load to the heavy load. it can.
JP 2007-115871 A

  However, in the switching power supply device 200 as described above, the loss generated in the drive circuit 108 cannot be ignored. Examples of the loss generated in the drive circuit 108 include a drive loss for driving the voltage controlled switching element 25. This drive loss is calculated by the following equation 1. Here, P is the power loss [W], Qg is the gate charge amount [C] required to drive the voltage controlled switching element, Vgs is the gate voltage [V], and f is the drive frequency [Hz].

P = Qg × Vgs × f (Formula 1)

  Equation 1 shows that the higher the gate charge amount Qg, the output gate voltage Vgs, and the drive frequency f, the greater the loss (power consumption, heat generation amount) of the drive circuit. Further, since the gate charge amount Qg increases as the gate voltage increases, it can be said that the loss of the driving circuit 108 depends greatly on the gate voltage.

  That is, driving the MOSFET with a high gate voltage reduces the loss caused by the MOSFET, while increasing the loss caused by the drive circuit. In particular, in the RCC switching power supply device 200, the frequency becomes high when the load is light, and it becomes difficult to reduce the power consumption of the switching power supply device 200 during standby.

  Note that even devices that have both MOSFET operation and IGBT operation that have been proposed in recent years are driven by a high gate voltage to fully utilize the current capability of the IGBT operation, and similarly it is difficult to reduce power consumption during standby. . The current capability is the maximum current value of the device at a certain gate voltage.

  Further, when the voltage-controlled switching element 25 is driven with a high gate voltage, there is a risk that the switching element may be destroyed when an abnormality such as a load short circuit occurs. The causes of destruction are as follows. The current capability of the voltage-controlled switching element 25 is increased by high gate voltage driving, and a large current flows immediately after turn-on due to a load short circuit or the like. However, in many switching power supply apparatuses, a blanking time for invalidating the overcurrent protection function is provided for a predetermined period of time in order to prevent erroneous detection of overcurrent protection immediately after the switching element is turned on. Therefore, a large current flows until the overcurrent protection function is activated, and there is a possibility that the surge voltage or noise generated at the time of turn-off causes element destruction or malfunction of other electronic devices. In particular, in a switching element such as an IGBT, a parasitic thyristor operates due to a large current, and may not be turned off and may be destroyed by latch-up.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to minimize the loss of the entire switching power supply device including the drive loss generated in the drive circuit and the conduction loss generated in the voltage control type switching element. Another object of the present invention is to prevent the switching element from being destroyed due to an abnormality such as a load short circuit.

In order to achieve the above object, a drive circuit according to the present invention is a drive circuit that drives a power switching element in a switching power supply, and is a drive signal for turning on and off the power switching element, Generation means for generating a drive signal having a plurality of levels of voltages for turning on the power switching elements, and switching control for switching the plurality of levels of voltages for turning on the power switching elements according to the state of the power switching elements And the plurality of levels of voltages include a first voltage and a second voltage lower than the first voltage, and the generation means includes a first driver that generates the first voltage, and the first voltage A second driver for generating two voltages, and the switching control means turns on when the load current is equal to or lower than a first threshold value. As the drive signal, the first driver and the second driver are controlled so that the level generates a pulse of the second voltage, and is turned on when the load current is larger than the first threshold value. The first driver and the second driver are controlled so as to generate a pulse of the first voltage at the level as the drive signal .

Thereby, since the voltage of several levels is switched, a drive loss and conduction | electrical_connection loss can be suppressed. Further, when the load current is below the threshold value, the drive loss can be reduced. On the other hand, when the load current is larger than the threshold value, the conduction loss can be reduced.

  Further, the switching control means may switch the voltages at the plurality of levels so that the voltage increases as the load current flowing through the power switching element increases.

  Thereby, when the load current is small, the drive loss can be reduced. Further, when the load current is large, the conduction loss can be reduced.

  The generation unit may further include a current limiting unit that limits a power supply current supplied to at least one of the first driver and the second driver.

  As a result, at least one of the first voltage pulse and the second voltage pulse generated by the first driver and the second driver has a gentle slope. Therefore, since high frequency components can be reduced, noise generated from the drive circuit can be suppressed.

  The drive circuit further detects whether or not the load current is greater than the first threshold value and exceeds a second threshold value indicating an overcurrent reference. An overcurrent protection circuit for stopping the circuit and a disable circuit for disabling the first driver for a period corresponding to a period from when the overcurrent is detected to when it is stopped may be provided.

  This prevents destruction of the power switching element due to latch-up when an overcurrent occurs.

  The switching control means generates a first control pulse signal for enabling the output of the first driver when the load current is larger than the first threshold value, and the second driver The level of the second voltage is generated according to a second control pulse signal indicating a period during which the power switching element is turned on and a period during which the power switching element is turned off, and the disable circuit outputs the second control pulse signal for a predetermined time. A delay circuit for delaying and a gate circuit for outputting a logical product of the delayed second control pulse signal and the first control pulse signal to the first driver may be provided.

  As a result, only the second voltage from the second driver is output within a predetermined time, and the first voltage from the first driver is not output. Therefore, it is possible to limit a large current that flows when an abnormality such as a load short circuit occurs. That is, it is possible to prevent the switching element from being destroyed at the time of abnormality. In particular, a switching element having a parasitic thyristor structure such as an IGBT is effective in preventing latch-up and preventing breakdown.

  Further, the switching control means controls the second driver so that a level of the pulse of the second voltage is generated as the drive signal to be turned on when the load current is not more than the first threshold value. When the load current is larger than the first threshold, the drive signal to be turned on generates a two-stage pulse whose level rises to the second voltage and then rises to the first voltage. The first driver and the second driver may be controlled.

  As a result, the voltage immediately after the rise of all the drive signals becomes the second voltage, so that when the drive signal is turned on, the drive signal is turned on from off compared to the case where the drive signal is raised to the first voltage in one step. It is possible to reduce the generation of noise when switching to. Further, when measuring the load current on the primary side, after the power switching element is turned on, it is detected that the gradually increasing load current exceeds the first threshold value and the gate voltage is switched. Practical control is possible.

  The switching control means generates a first control pulse signal for enabling the output of the first driver when the load current is larger than the first threshold value, and the first driver And a first transistor to which a pulse signal obtained by ANDing the first control pulse signal and the second control pulse signal is applied to a gate, and the second driver includes: A second transistor to which the second voltage is applied to a source and the second control pulse signal indicating a period for turning on and off the power switching element is applied to a gate; A backflow prevention diode connected between the drain of the first transistor and the drain of the second transistor to prevent backflow of current; And a third transistor complementarily turning on or off the transistor, and the drain of the first transistor, and the cathode of the blocking diode, and a drain of the third transistor may be connected.

  Thus, the drive circuit can be easily configured by using a transistor.

The driving method according to the present invention is a driving method for driving a power switching element in a switching power supply device, wherein the power switching element has a first voltage and a second voltage lower than the first voltage. The driving method compares a load current flowing through the power switching element with a threshold value, and generates the first voltage when the load current is larger than the threshold value. by controlling the first driver and a second driver configured to generate the second voltage, a pulse of pre-Symbol first voltage as an oN signal is supplied to the power switching element, the load current is less than the threshold value when, by controlling the first driver and the second driver, the pulse before Symbol second voltage as an oN signal, supplied to said power switching element That.

The switching power supply device according to the present invention is driven and generated by a diode bridge that rectifies an input AC signal, a power switching element that switches the rectified voltage, and a drive circuit that drives the power switching element. A transformer that receives the converted voltage and converts it to a different voltage, and a rectifying and smoothing circuit that rectifies and smoothes the converted voltage, and outputs the power switching element. Generating means for generating a drive signal having a plurality of levels of voltages for turning on the power switching element; and the plurality of levels for turning on the power switching element according to a state of the power switching element and a switching control means for switching the voltage, the multi-level voltage, the first collector And a second voltage lower than the first voltage, and the generation means includes a first driver that generates the first voltage and a second driver that generates the second voltage, and the switching control. The means controls the first driver and the second driver so that a level of the second voltage pulse is generated as the drive signal to be turned on when the load current is less than or equal to a first threshold value. When the load current is larger than the first threshold, the first driver and the second driver are controlled so that a level of the first voltage pulse is generated as the drive signal to be turned on. .

  The switching element may be a unipolar transistor.

  The conduction resistance of a unipolar transistor has the property that it depends on the gate voltage as the load current value flowing through the unipolar transistor increases. That is, when the load current value is small, such as during light loads, the conduction resistance of the unipolar transistor does not increase even if the gate voltage is reduced. Therefore, since the voltage of the drive signal is switched based on the load current value flowing through the unipolar transistor, conduction loss and drive loss can be suppressed.

  The switching element may be a transistor having a function of switching between a unipolar operation and a bipolar operation in accordance with a load current flowing through the switching element.

  Thus, when a large current flows, the conduction resistance can be further lowered by bipolar operation and high gate voltage driving, and the driving loss can be lowered by unipolar operation and low gate voltage driving at a light load. Therefore, it is possible to comprehensively reduce main losses of the power supply device such as switching loss, conduction loss, and drive loss over the entire region from light load to heavy load.

  The switching power supply device further includes a measuring unit that measures a current output from the rectifying and smoothing circuit, and a conversion unit that converts the measured current into a load current flowing through the power switching element, The switching control means may switch the plurality of levels of voltages for turning on the power switching element according to the converted load current.

  According to the drive circuit according to the present invention, it is possible to minimize the loss of the entire power source including the drive loss generated in the drive circuit, the conduction loss generated in the power switching element, and the switching loss. Further, it is possible to prevent the power switching element from being destroyed at the time of start-up or an abnormality such as a load short circuit.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
The drive circuit according to the first embodiment is a drive circuit that drives a power switching element in a switching power supply, and is a drive signal for turning on and off the power switching element, and the power switching element is turned on. Generating means for generating a drive signal having a plurality of levels of voltage, and switching control means for switching the plurality of levels of voltages for turning on the power switching element according to the state of the power switching element.

  FIG. 1 is a diagram illustrating a configuration of a switching power supply device including the drive circuit according to the first embodiment.

  The switching power supply apparatus 100 according to the present embodiment is an RCC system, and includes a primary side rectifying / smoothing circuit 101, a switching circuit 102, a transformer 103, a secondary side rectifying / smoothing circuit 104, and a feedback circuit 119.

  The primary-side rectifying / smoothing circuit 101 includes a diode bridge 109 and an input capacitor 110, rectifies the input AC signal by the diode bridge 109, smoothes it by the input capacitor 110, and outputs it to the switching circuit 102.

  The switching circuit 102 switches the voltage-controlled switching element at high speed and outputs high-frequency alternating current to the transformer 103. Specifically, the switching circuit 102 includes an external resistor 121 of the drive circuit 20, a resonance capacitor 122, the drive circuit 20, and a voltage control type switching element 25.

  The drive circuit 20 is supplied with power via an external resistor 121 of the drive circuit when the switching power supply device 100 is activated. Next, the drive circuit 20 applies a voltage to the gate of the voltage-controlled switching element 25 to perform a switching operation. Note that the drive circuit 20 is operated by electric power supplied from the auxiliary winding of the transformer 103 at times other than startup.

  The drive circuit 20 includes a switching control unit and a generation unit, and the switching control unit switches the plurality of levels of voltage so that the voltage becomes higher as the load current flowing through the power switching element increases. The voltage includes a first voltage and a second voltage lower than the first voltage, and the generating means includes a first driver that generates the first voltage and a second driver that generates the second voltage. And the switching control means generates the pulse of the second voltage at the level as the drive signal to be turned on when the load current is equal to or lower than a first threshold value. The second driver is controlled, and when the load current is larger than the first threshold value, the level is generated as a pulse of the first voltage as the drive signal to be turned on. Controlling said first driver and said second driver.

  The transformer 103 transmits energy from the primary side to the secondary side. Specifically, it has a primary winding 111, a secondary winding 112, and an auxiliary winding 120. When the voltage controlled switching element 25 is turned on, the energy stored in the primary winding 111 is transmitted to the secondary winding 112. After that, when the secondary current flowing in the secondary winding 112 disappears, the inductance of the primary winding 111 of the transformer 103 and the resonance capacitor 122 inserted between the drain and source of the voltage-controlled switching element 25 The resonance operation determined by the capacitance is started. The drive circuit 20 detects the above-described resonance operation and applies the next drive signal 132 to the voltage-controlled switching element 25.

  The AC signal generated by the switching operation as described above is transmitted to the secondary side rectifying / smoothing circuit 104 via the secondary winding 112 of the transformer 103.

  The secondary-side rectifying / smoothing circuit 104 includes a rectifying diode 113, a first output capacitor 115, a choke coil 114, and a second output capacitor 116, and rectifies the AC transmitted to the secondary winding 112. Rectified by the diode 113, smoothed by the choke coil 114, the first output capacitor 115 and the second output capacitor 116, and output as the output of the switching power supply device 100.

  The feedback circuit 119 drives the feedback signal 133 so that the current value output from the secondary side rectifying / smoothing circuit 104, that is, the output voltage that changes in accordance with the power supply output current Io of the switching power supply device 100 is kept constant. Feedback to 20. The drive circuit 20 controls the load current flowing through the voltage-controlled switching element 25 according to the fed-back state on the secondary side. The feedback circuit 119 includes, for example, a photocoupler, and feeds back a current value via the photocoupler.

  FIG. 2 is a diagram illustrating a configuration of the drive circuit 20, the voltage control switching element 25, and the feedback circuit 119 according to the first embodiment. The drive circuit 20 in the figure is a circuit that generates and outputs a drive signal 132 that is a signal for driving the voltage-controlled switching element 25. The drive signal 132 is a signal for turning on and off the voltage controlled switching element 25. The drive circuit 20 includes a control circuit 21, a load current detection circuit 27, and a drive voltage switching circuit 22.

  The control circuit 21 outputs to the drive voltage switching circuit 22 a control signal 134 that is a signal indicating a period during which the voltage controlled switching element 25 is turned on and a period during which the voltage controlled switching element 25 is turned off. Specifically, the control circuit 21 detects a resonance operation determined by the inductance of the primary winding 111 of the transformer 103 and the capacitance value of the resonance capacitor 122 and turns on the control signal 134. Further, the control circuit 21 turns off the control signal 134 when any one of the following conditions is satisfied. When the load current flowing through the voltage controlled switching element 25 reaches a current value determined by the feedback signal 133, when the on time of the voltage controlled switching element 25 reaches the maximum on time set by the control circuit 21, This is a case where the current flowing through the voltage controlled switching element 25 reaches a predetermined overcurrent protection reference voltage VLIMIT. The overcurrent protection reference voltage VLIMIT is specified by, for example, the characteristics of the voltage control type switching element 25.

  Although not particularly illustrated, the control circuit 21 has a function of adjusting a load current that flows through the voltage-controlled switching element 25 when the feedback signal 133 is input.

  The load current detection circuit 27 includes, for example, a comparator, determines whether or not the load current determined from the feedback signal 133 exceeds a predetermined threshold value, and indicates whether or not the load current is exceeded. 135 is output to the drive voltage switching circuit 22. If it is determined that the value has exceeded, the load current detection circuit 27 sets the load current detection signal 135 to high, for example. When it is determined that the value does not exceed the load current detection circuit 27, for example, the load current detection signal 135 is set to low.

  The drive voltage switching circuit 22 is a signal for turning on and off the voltage controlled switching element 25, generates a drive signal 132 having a plurality of levels of voltages for turning on the voltage controlled switching element 25, and controls the voltage. Applied to the gate of the type switching element 25. Specifically, the drive voltage switching circuit 22 applies a drive signal 132 for turning on the voltage control type switching element 25 to the gate of the voltage control type switching element 25 when the control signal 134 indicates a period to be turned on. . The voltage of the drive signal 132 is switched according to the load current detection signal 135 output from the load current detection circuit 27.

  Next, the detailed configuration of the drive voltage switching circuit 22 will be described.

  FIG. 3 is a block diagram showing a more detailed configuration.

  The drive voltage switching circuit 22 includes a gate voltage switching circuit 2, a high voltage driver 3, a low voltage driver 4, a first switch SW1, and a second switch SW2. Here, the high voltage driver 3 and the low voltage driver 4 function as generating means for generating a drive signal having a plurality of levels of voltages for turning on the voltage control type switching element 25. The gate voltage switching circuit 2, the first switch SW 1, and the second switch SW 2 switch a plurality of levels of voltages for turning on the voltage controlled switching element 25 according to the state of the voltage controlled switching element 25. It functions as a switching control means. As a specific configuration, a circuit in which the first switch SW1 is connected in series at the subsequent stage of the high voltage driver 3 and a circuit in which the second switch SW2 is connected in series at the subsequent stage of the low voltage driver 4 are connected in parallel. Has been.

  In accordance with the load current detection signal 135, the gate voltage switching circuit 2 makes the first switch SW1 or the second switch SW2 conductive and cuts the other. For example, when the load current detection signal 135 is high, the gate voltage switching circuit 2 turns on the first switch SW1 and cuts off the second switch SW2. When the load current detection signal 135 is low, the gate voltage switching circuit 2 cuts off the first switch SW1 and makes the second switch SW2 conductive. Accordingly, the drive voltage switching circuit 22 applies the voltage generated by the high voltage driver 3 or the voltage generated by the low voltage driver 4 to the voltage controlled switching element 25. Here, the power supply voltage of the high voltage driver 3 is Vdd1, and the power supply voltage of the low voltage driver 4 is Vdd2 (Vdd1> Vdd2).

  As described above, the multi-level voltage includes Vdd1 and Vdd2 lower than Vdd1, and the generation unit includes the high voltage driver 3 that generates Vdd1 and the low voltage driver 4 that generates Vdd2, and performs switching control. When the load current flowing through the voltage-controlled switching element 25 is equal to or lower than a predetermined threshold value Idsth, the means generates a pulse having a level of Vdd2 as the drive signal 132 to be turned on. When the low voltage driver 4 is controlled and the load current is larger than Idsth, the high voltage driver 3 and the low voltage driver 4 are controlled so as to generate a pulse having a level of Vdd1 as the drive signal 132 to be turned on. As a result, when the load current is less than or equal to the threshold value, the drive loss can be reduced. Further, when the load current is larger than the threshold value, the conduction loss can be reduced.

  FIG. 4 is a diagram showing the relationship between the load connected to the switching power supply apparatus 100 and the sum of drive loss, conduction loss, and switching loss (hereinafter referred to as total loss) which are main losses.

  FIG. 5 is a diagram showing the magnitude of each loss in the standby state and the rated load state shown in FIG. Here, each loss will be described.

  The driving loss is a loss expressed by Equation 1, which indicates a power loss consumed by the gate capacitance of the voltage-controlled switching element 25, and greatly depends on the gate voltage and the switching frequency. Accordingly, when the drive loss is compared between the standby state and the rated load state at the same gate voltage, the drive loss increases in the standby state where the switching frequency is high. Further, when different gate voltages are compared in the same state, the drive loss becomes large at Vdd1 having a high gate voltage.

  Further, the conduction loss indicates a power loss represented by the product of the flowing current and the conduction resistance during the period in which the voltage controlled switching element 25 is conducting, and greatly depends on the conduction resistance. Here, when the voltage controlled switching element 25 is a power MOSFET, a conduction resistance generated in the power MOSFET will be described.

  FIG. 6 is a graph showing the VI characteristics of the power MOSFET.

  In the same figure, the VI characteristic in the case of two voltage levels Vdd1 and Vdd2 having different gate voltages Vgs is shown. Idsth is a drain current value at which the gate voltage dependency of the power MOSFET starts to increase.

  As can be seen from the figure, the current capability of the power MOSFET increases as the gate voltage Vgs increases. Therefore, by setting the gate voltage Vgs high, the conduction resistance can be reduced and conduction loss can be suppressed. However, in the region where the drain current Ids is small, the conduction resistance does not greatly depend on the gate voltage Vgs, so that the conduction loss due to the gate voltage Vgs is equal.

  The switching loss is a power loss that appears at the moment when the voltage-controlled switching element 25 is turned on or turned off. Therefore, loss increases in a standby state with a high switching frequency.

  As described above, the conduction loss, the driving loss, and the switching loss are in a trade-off relationship. However, the proportion of conduction loss is dominant in the rated load state, and suppressing conduction loss leads to suppression of total loss.

  Therefore, the threshold value of the load current detected by the load current detection circuit 27 is set to Idsth. The load current detection circuit 27 determines whether or not the drain current Ids is larger than Idsth. If the drain current Ids is larger than Idsth, the load current detection signal 135 is made high, and if it is less than Idsth, it outputs low. For example, when the load current detection circuit 27 is configured by a comparator or the like, and compares the reference value with the load current and outputs the load current detection signal 135, the load current detection circuit 27 includes the voltage controlled switching element 25. From the V-I characteristic, a drain current value having a large gate voltage dependency is read, and the current value is defined as Idsth.

  Here, the gate voltage dependency means that the conduction resistance (= drain voltage / drain current) of the voltage-controlled switching element 25 changes depending on the gate voltage, and the state where the gate voltage dependency becomes large When the drain current is increased, the channel resistance of the voltage-controlled switching element 25 cannot be ignored, and the conduction resistance can be varied depending on the gate voltage. In the above description, it is described that the drain current value at which the gate voltage dependency of the power MOSFET starts to increase is set as the threshold value of the comparator in the load current detection circuit 27. However, the ratio between the drive loss and the conduction loss is considered. For example, the load current detection circuit 27 calculates a load current value at which the difference in conduction resistance between the two levels of gate voltage is a predetermined value, for example, the conduction resistance when the gate voltage is high is 5% lower than when the gate voltage is low. It may be set as the threshold value of the comparator.

  As a result, the drive loss of the drive circuit can be reduced without increasing the conduction loss even when the gate voltage is lowered at light load. On the other hand, since the gate voltage can be increased and the conduction loss can be reduced under heavy load, the loss of the entire switching power supply device 100 including the drive loss caused by the drive circuit and the conduction loss caused by the voltage-controlled switching element can be reduced. It can be minimized from the load to the heavy load.

  As described above, overall loss reduction over a wide range from a light load to a heavy load can be realized by switching the gate voltage of the voltage controlled switching element 25 according to the load. In particular, reducing the loss in a region where the load is very small, that is, in the standby state, can greatly contribute to reducing the standby power of home appliances and the like.

  Next, the operation of the switching power supply device 100 including the drive circuit 20 described above will be described.

  FIG. 7 is a timing chart showing the power supply output current Io and the power supply output voltage Vo of the switching power supply apparatus 100 according to the present embodiment and the drain current and the gate voltage of the voltage controlled switching element 25 for different load states.

  In the rated load state, a large amount of power output current Io that is a current output from the switching power supply apparatus 100 flows. At this time, the load current detection circuit 27 determines whether or not the peak current of the drain current Ids flowing through the voltage controlled switching element 25 is larger than Idsth based on the feedback signal 133. When it is determined that the load current is large, the load current detection circuit 27 outputs, for example, high as the load current detection signal 135.

  When the load current detection signal 135 is high, the gate voltage switching circuit 2 turns on the first switch SW1 connected to the high voltage driver 3 and turns off the second switch SW2. As a result, the drive circuit 20 outputs a pulse signal having a high-level voltage Vdd1 as the drive signal 132.

  Next, in the load fluctuation state, which is a transition period from the rated load state to the standby state, the load is gradually reduced, so that the power supply output current Io decreases, and the power supply output voltage Vo increases accordingly. When Vo rises, the control circuit 21 gradually reduces the pulse width of the control signal 134, thereby changing the pulse width of the drive signal 132 in the same manner to suppress the drain current Ids. Further, since the peak current of the drain current Ids is larger than Idsth, the gate voltage switching circuit 2 keeps the first switch SW1 conductive. As a result, the drive circuit 20 outputs a pulse signal having a high-level voltage Vdd1 as the drive signal 132.

  In the standby state, the power output current Io further decreases and the power output voltage Vo increases. When Vo is high, the control circuit 21 further suppresses the peak current of the drain current Ids by further narrowing the pulse width of the control signal 134. When the load current detection circuit 27 detects that the drain current Ids is equal to or lower than Idsth, the load current detection circuit 27 outputs, for example, low as the load current detection signal 135. When the load current detection signal 135 is low, the gate voltage switching circuit 2 cuts off the first switch SW1 and makes the second switch SW2 conductive. As a result, the drive circuit 20 outputs a pulse signal having a high-level voltage Vdd2 as the drive signal 132.

  As described above, the drive circuit 20 according to the present embodiment has the drive signal that turns on the voltage control switching element 25 when the load current flowing through the voltage control switching element 25 is equal to or less than a predetermined threshold value. A pulse having a level of Vdd2 is generated as 132, and a pulse having a level of Vdd1, which is higher than Vdd2, is generated as a drive signal 132 for turning on the voltage-controlled switching element 25 when the level is greater than a predetermined threshold value. To do.

  Therefore, drive circuit 20 according to the present embodiment can reduce drive loss when the load current is equal to or less than a predetermined threshold value. Further, when the load current is larger than a predetermined threshold value, the conduction loss can be reduced.

  In the first embodiment, the case where the power MOSFET as shown in FIG. 6 is connected to the drive circuit 20 as the voltage control type switching element 25 has been described. However, the present invention is not limited to this. . For example, instead of the power MOSFET, a device having both a unipolar MOSFET and a bipolar IGBT may be connected to the drive circuit 20 as the voltage-controlled switching element 25.

  FIG. 8 is a circuit diagram showing an equivalent circuit of a device having both a MOSFET and an IGBT disclosed in Patent Document 1. The equivalent circuit 80 is a circuit having a function of switching between a unipolar operation and a bipolar operation.

  FIG. 9 is a graph showing the VI characteristics of a device having both a MOSFET and an IGBT.

  In a device having both a MOSFET and an IGBT, a unipolar transistor 81 having a fast switching operation operates in a standby state with a small load current, and a bipolar transistor 83 capable of flowing a large current operates in a rated load state with a large load current. Compared with the VI characteristic of the general power MOSFET shown in FIG. 6, the conduction resistance in the rated load state can be further reduced, so that conduction loss can be suppressed. In this case, the threshold value used as a reference for comparison by the load current detection circuit 27 is set to, for example, a drain current value at which the MOSFET operation is switched to the IGBT operation.

  The first embodiment is not limited to FIG. In the first embodiment, the drive circuit that switches between two types of gate voltages has been described. However, a drive circuit that switches between two or more types of gate voltages may be used.

  The switching power supply apparatus 100 includes, for example, an ammeter that measures a load current value instead of the feedback circuit 119, and the load current detection circuit 27 loads the load current detection signal 135 according to the measured load current value. May be output. FIG. 10 is a diagram illustrating a configuration including an ammeter instead of the feedback circuit 119 of the first embodiment. FIG. 11 is a diagram showing a more detailed configuration. The ammeter 26 is connected to the drain of the voltage controlled switching element 25, directly measures the load current value, and outputs it to the load current detection circuit 27 as a load current signal 141. The load current detection circuit 27 compares the output load current value with Idsth and outputs a load current detection signal 135 to the gate voltage switching circuit 2.

  In addition, the drive circuit 20 may switch the gate voltage by detecting a change in the voltage-controlled switching element 25 or other parts in the switching power supply device 100. For example, a change in voltage induced in the auxiliary winding 120 in FIG. 1 may be used.

  In addition, in consideration of temperature characteristics and manufacturing variations of the voltage control type switching element 25, a gate voltage which is a voltage for driving the voltage control type switching element 25 is switched by a method developed from the above method or other methods. A threshold may be set. Hereinafter, in this specification, a drive voltage and a gate voltage are synonymous.

  Further, when the switching power supply device is used in home appliances or the like, if the operation state is only two states, for example, a standby state and a rated load state in FIG. 7, the voltage of the drive signal 132 is changed from Vdd2 to Vdd1. Switching timing has little effect on power efficiency. Therefore, when the peak value of the drain current in the rated load state is Idsth2, the threshold value may be any value in which the current value flowing through the voltage controlled switching element 25 is larger than Idsth and smaller than Idsth2. That is, the plurality of levels of voltages for turning on the power switching element include a first voltage and a second voltage lower than the first voltage, and the generation means includes a first driver that generates the first voltage, A switching driver that generates a pulse having a first voltage level as a drive signal to be turned on when a load current flowing through the power switching element is greater than a first threshold value. As described above, when the first driver and the second driver are controlled and the load current flowing through the power switching element is equal to or lower than the second threshold value which is smaller than the first threshold value, the level is set to the second voltage as the drive signal to be turned on. The first driver and the second driver are controlled so as to generate the following pulses.

  In the first embodiment, the threshold value at which the drive circuit 20 switches the gate voltage is determined based on the gate voltage dependency. However, the load current detection circuit 27 has a solid line in FIG. The drain current corresponding to the intersection between the dotted line (when Vdd1) and the dotted line (when low gate voltage Vdd2) may be used as the threshold value. That is, the gate may be driven with the low gate voltage Vdd2 until the total loss is reversed. Further, the threshold value may be set intentionally high or low. For example, it may be set higher than Idsth in consideration of the ratio of the drive loss generated in the drive circuit 20 and the conduction loss generated in the voltage-controlled switching element 25. Further, the threshold value may be adjusted externally so that the loss of the switching power supply device 100 is optimally reduced.

  In the first embodiment, the RCC switching power supply device 100 as shown in FIG. 1 has been described. However, the switching power supply device to which the drive circuit 20 according to the present invention can be applied is limited to FIG. is not. For example, an effect similar to that of the present invention can be obtained as long as the driving circuit is driven while controlling the width of the on-pulse of the voltage-controlled switching element having inductive loads connected in series or the peak current.

(Embodiment 2)
The drive circuit according to the second embodiment controls the second driver so as to generate a pulse of the second voltage as a drive signal to be turned on when the load current is equal to or less than the threshold value. From the first driver and the first voltage that generate the first voltage so as to generate a two-stage pulse that rises to the second voltage and then rises to the first voltage as the drive signal to be turned on when the threshold is larger than the threshold value A second driver that generates a low second voltage is controlled.

  The configuration of the drive circuit according to the present embodiment is the same as that of FIG. 2, and the configuration of the switching power supply device including the drive circuit according to the present embodiment is the same as that of FIG. The same explanation as is not repeated.

  Next, the operation of the switching power supply device including the drive circuit according to the second embodiment will be described.

  FIG. 12 shows the power supply output current Io and the power supply output voltage Vo in each load state, the drain current Ids and the gate voltage of the voltage-controlled switching element 25 in the switching power supply device 100 including the drive circuit 20 according to the second embodiment. It is a timing chart which shows Vgs. Hereinafter, the difference between the drive circuit 20 according to the present embodiment and the first embodiment will be specifically described.

  Based on the feedback signal 133, the load current detection circuit 27 according to the first embodiment compares the peak current of the drain current Ids flowing through the voltage-controlled switching element 25 with a predetermined threshold value Idsth to determine the gate voltage. It was selected whether to set Vgs to Vdd1 or Vdd2. On the other hand, in the load current detection circuit 27 of the second embodiment, when the peak current of the drain current Ids flowing through the voltage controlled switching element 25 is larger than the threshold value Idsth, the gate voltage Vgs first rises to Vdd2, The load current detection signal 135 is output so as to rise to Vdd1 after being maintained at Vdd2 for a certain period.

  Therefore, when the load current detection signal 135 changes from low to high during the period in which the drive signal 132 is on, the gate voltage switching circuit 2 turns on the first switch SW1 and cuts off the second switch SW2. Thus, the gate voltage Vgs is switched from Vdd2 to Vdd1. That is, the drive circuit 20 according to the second embodiment sets the low gate voltage Vdd2 immediately after the ON drive signal 132 is output, and sets the high level within the high level period of one pulse of the drive signal 132 as necessary. It can be switched to the gate voltage Vdd1.

  As a result, the voltage immediately after the rise of all the drive signals 132 becomes Vdd2, so that when the drive signal 132 is turned on, the high-frequency component is increased compared to the first embodiment in which the high gate voltage Vdd1 is raised in one step. Therefore, the generation of noise when the drive signal 132 is switched from OFF to ON can be reduced. Also, as shown in FIGS. 10 and 11, when the load current is measured on the primary side, it is detected that the gradually increasing load current exceeds Idsth after the voltage-controlled switching element 25 is turned on. Thus, more practical control such as switching the gate voltage Vgs is possible.

(Embodiment 3)
In addition to the function of the second embodiment, the drive circuit according to the third embodiment detects and fixes the overcurrent to the low gate voltage when the overcurrent flows through the voltage controlled switching element. The current capability of the element is limited, and breakdown due to latch-up of the voltage controlled switching element is prevented.

  FIG. 13 is a diagram showing the configuration of the drive circuit, voltage-controlled switching element 25, and ammeter 26 according to the third embodiment. In the figure, the same components as those of the drive circuit 20 according to the second embodiment are denoted by the same reference numerals. Therefore, in the present embodiment, the same description as that of the drive circuit 20 according to the second embodiment is not repeated. Hereinafter, the difference between the drive circuit according to the present embodiment and the drive circuit 20 according to the second embodiment will be specifically described.

  The drive circuit 50 according to the third embodiment further includes a disable circuit 51 and an overcurrent protection circuit 52 as compared with the drive circuit 20 according to the second embodiment shown in FIG. The disable circuit 51 disables the high-voltage driver 3 for a period corresponding to a period from when the overcurrent flowing through the voltage-controlled switching element 25 is detected until the drive circuit 50 is stopped. Specifically, the disable circuit 51 includes a delay circuit 53 and an AND gate 54.

  The delay circuit 53 delays the control signal 134 output from the control circuit 21 by a predetermined delay time Tdelay and outputs the delayed signal 136 to the AND gate 54. Here, Tdelay needs to be longer than the time from when the overcurrent protection circuit 52 detects the overcurrent to when the drive circuit 50 stops.

  The AND gate 54 takes a logical product of the delay signal 136 output from the delay circuit 53 and the load current detection signal 135 output from the load current detection circuit 27 and outputs the logical product to the gate voltage switching circuit 2. Therefore, unlike the second embodiment, the gate voltage switching circuit 2 detects that the load current detection circuit 27 has exceeded the Idsth of the drain current Ids flowing through the voltage-controlled switching element 25, and sets the load current detection signal 135 to the high level. Even in this case, the first switch SW1 and the second switch SW2 are not switched during the period when the delay signal 136 is low.

  The overcurrent protection circuit 52 includes, for example, a comparator, and the drain current Ids flowing through the voltage controlled switching element 25 measured by the ammeter 26 exceeds a predetermined threshold value Idsoc indicating an overcurrent reference. The overcurrent detection signal 55 indicating the result of the determination is output to the control circuit 21. For example, the overcurrent protection circuit 52 sets the overcurrent detection signal 55 high when the drain current Ids exceeds Idsoc, and sets the overcurrent detection signal 55 low when the drain current Ids is equal to or less than Idsoc.

  When the overcurrent detection signal 55 is low, the control circuit 21 performs the same control as in the second embodiment. When the overcurrent detection signal 55 is high, the control signal 134 is set low and the drive circuit 50 is stopped. Therefore, when an overcurrent is detected, the voltage controlled switching element 25 is turned off.

  Next, the operation of the drive circuit 50 according to the third embodiment will be described.

  FIG. 14 is a timing chart showing the operation of the drive circuit 50 according to the third embodiment in a normal state and an overcurrent state.

  (A) shows the drain current Ids and the gate voltage Vgs when the delay circuit 53 is provided, and (b) shows the drain current Ids and the gate voltage Vgs when the delay circuit 53 is not provided. The delay signal 136 is a signal delayed from the control signal 134 by a delay time Tdelay. Tsd is the time from when the overcurrent protection circuit 52 detects an overcurrent until the control circuit 21 sets the control signal 134 to low to stop the drive circuit 50. Idslu is a drain current value at which the voltage controlled switching element 25 is destroyed by latch-up. The normal state is any of the rated load state, the load fluctuation state, and the standby state of the second embodiment. The overcurrent state is a state in which, for example, a short circuit occurs and a large current flows on the output side of the switching power supply device 100.

  In the normal state, both of (a) and (b), as in the second embodiment, when the control signal 134 is turned on, the drive voltage switching circuit 22 generates a pulse with the high level voltage of the drive signal 132 as Vdd2. Output. Along with this, the drain current Ids gradually increases. The delay signal 136 is turned on with a delay time Tdelay after the control signal 134 is turned on. Next, when the drain current Ids exceeds the threshold value Idsth and the delay signal 136 is at a high level, the gate voltage switching circuit 2 makes the first switch SW1 conductive and cuts off the second switch SW2. The gate voltage Vgs is Vdd1.

  In the overcurrent state, the drain current Ids increases rapidly. At this time, in (a), when the delay signal 136 is low even if the drain current Ids exceeds Idsth, the output of the AND gate 54 is low, and the gate voltage switching circuit 2 is switched between the first switch SW1 and the second switch SW2. Do not switch. Therefore, the drive signal 132 remains a pulse signal having a level of Vdd2. That is, the gate voltage Vgs is always equal to or lower than Vdd2 during Tdelay after the control signal 134 is turned on.

  On the other hand, since the delay circuit 53 is not provided in (b), when the drain current Ids exceeds the threshold value Idsth, the gate voltage switching circuit 2 turns on the first switch SW1 and cuts off the second switch SW2. To do. Therefore, the voltage of the drive signal 132 rises from Vdd2 to Vdd1.

  Since the maximum value of the drain current Ids increases as the gate voltage Vgs increases, when the maximum values of the drain current Ids in the overcurrent state are compared with each other in (a) and (b), the gate voltage Vgs is low (a). The maximum value of the drain current Ids becomes lower than (b).

  Therefore, for example, when Idslu is between the maximum value of the drain current Ids that flows when the gate voltage Vgs is Vdd2 and the maximum value of the drain current Ids that flows when the gate voltage is Vdd1, the following is obtained. . In (b), since the drain current Ids exceeds the threshold value Idsoc serving as a reference indicating overcurrent and further exceeds Idslu, the overcurrent continues to flow, and the voltage controlled switching element 25 is destroyed by latch-up. . However, in (a), since the gate voltage is Vdd2, the drain current Ids does not exceed Idslu, and when the control signal 134 becomes low after the Tsd time has elapsed since the drain current Ids exceeded Idsoc, the drive circuit Since 50 is stopped, the voltage-controlled switching element 25 is not destroyed by latch-up.

  As described above, in the drive circuit 50 according to the third embodiment, the time Tsd from when the overcurrent protection circuit 52 detects overcurrent until the control circuit 21 sets the control signal 134 to low is low gate voltage. To suppress the current capability of the voltage-controlled switching element 25. Thereby, the large current which flows at the time of abnormality, such as a load short circuit, can be restrict | limited. That is, it is possible to prevent the voltage-controlled switching element 25 from being broken due to a large current flowing in an abnormal state. In particular, a switching element having a parasitic thyristor structure such as an IGBT is effective in preventing latch-up and preventing breakdown.

  The threshold value Idsoc serving as a reference indicating overcurrent is determined by the feedback signal from the feedback circuit 119 as the drain current value corresponding to the overcurrent protection reference voltage VLIMIT or the drain current flowing through the voltage controlled switching element 25. Current value. In general, the overcurrent protection circuit 52 has a delay time from when the voltage-controlled switching element 25 is turned on until it functions.

  Moreover, although the load short circuit was mentioned as an example at the time of overcurrent protection operation | movement, it has the same effect also with respect to the rush current at the time of starting of the switching power supply device 100. FIG.

(Embodiment 4)
The drive circuit according to the fourth embodiment is substantially the same as the drive circuit 20 according to the second embodiment, except that it includes a current limiting unit that limits the power supply current supplied to the high-voltage driver.

  FIG. 15 is a diagram showing the configuration of the drive circuit, voltage-controlled switching element 25, and feedback circuit 119 according to the fourth embodiment. In the figure, the same components as those of the drive circuit according to the second embodiment are denoted by the same reference numerals. Therefore, in the fourth embodiment, description similar to that of the drive circuit according to the second embodiment is not repeated. Hereinafter, the difference from the second embodiment in the drive circuit 60 according to the present embodiment will be specifically described.

  The drive circuit 60 according to the fourth embodiment further includes a constant current circuit 10 as compared with the drive circuit 20 according to the second embodiment. The constant current circuit 10 is a circuit that limits the power supply current supplied to the high voltage driver 3. Thereby, the waveform when the voltage level of the drive signal 132 rises to Vdd1 can be smoothed.

  FIG. 16 is a timing chart showing the power supply output current Io and the power supply output voltage Vo of the switching power supply apparatus according to the present embodiment, and the drain current and the gate voltage of the voltage controlled switching element 25 for different load states.

  In the drive circuit 60 according to the fourth embodiment, the gate voltage switching circuit 2 includes the first switch SW1 and the second switch when the load current detection signal 135 becomes high within the time when the control signal 134 is on. SW2 is controlled to switch the gate voltage Vgs from Vdd2 to Vdd1. At this time, since the constant voltage circuit 10 is connected to the high voltage driver 3, the gate charge current is limited, and the rise to Vdd1 becomes gentle.

  As described above, the drive circuit 60 according to the fourth embodiment limits the gate charge current on the high gate voltage side, thereby slowing the boosting speed when the gate voltage is switched and reducing the high frequency component. Can be suppressed.

  Note that the configuration of the drive circuit according to the present invention is not limited to FIG. 15 showing the fourth embodiment. In the fourth embodiment, the constant current circuit 10 is connected to the high voltage driver 3. For example, even if a gate resistance is connected between the high voltage driver 3 and the first switch SW1, the gate charge current is limited. Good. Further, the gate charge current may be limited by connecting a gate resistor between the low voltage driver 4 and the second switch SW2. The constant current circuit 10 may be connected to the low voltage driver 4 or may be connected to both the low voltage driver 4 and the high voltage driver 3.

  Further, the switching power supply device includes, for example, an ammeter that measures a load current value instead of the feedback circuit 119, and the load current detection circuit 27 outputs a load current detection signal 135 according to the measured current value. May be. FIG. 17 is a diagram illustrating a configuration including an ammeter instead of the feedback circuit 119 of the fourth embodiment.

(Embodiment 5)
The drive circuit according to the fifth embodiment controls the low voltage driver 4 as a drive signal to be turned on when the load current is less than or equal to the threshold value. Controls the high voltage driver 3 to generate a pulse of Vdd1.

  FIG. 18 is a circuit diagram of a drive voltage switching circuit provided in the drive circuit according to the fifth embodiment. Other than the drive voltage switching circuit in the drive circuit, it is the same as drive circuits 20 and 60 according to the first, second and fourth embodiments.

  The drive voltage switching circuit 70 includes a NAND circuit 41, inverter circuits 42 and 43, a high voltage application circuit 31, a low voltage application circuit 32, a turn-off circuit 33, and a backflow prevention diode 34.

  The NAND circuit 41 outputs a negative logical product of the load current detection signal 135 and the control signal 134 to the high voltage application circuit 31. Thereby, the high voltage application circuit 31 is driven when the load current detection signal 135 is high and the control signal 134 is high.

  Inverter circuit 42 outputs an inverted signal of control signal 134 to P-channel MOSFET 38, and inverter circuit 43 outputs an inverted signal of control signal 134 to N-channel MOSFET 39.

  The high voltage application circuit 31 functions as a first driver, and includes a level shift circuit 35, a P-channel MOSFET 36, and a constant current circuit 37.

  The level shift circuit 35 converts the logic driven by Vdd2 into the logic of Vdd1. As a result, the downstream P-channel MOSFET 36 can be completely turned off. The level shift circuit 35 may be a general circuit that converts a low voltage signal into a high voltage signal.

  In the P-channel MOSFET 36, Vdd1 is applied to the source via the constant current circuit 37, and the signal converted into the logic of Vdd1 by the level shift circuit 35 is input to the gate.

  The constant current circuit 37 limits the power supply current of the P-channel MOSFET 36.

  Therefore, in the high voltage application circuit 31, when the load current detection signal 135 is high and the control signal 134 is high, the P-channel MOSFET 36 is turned on and outputs Vdd1. Further, the rise to Vdd1 has a gentle slope.

  The low voltage application circuit 32 functions as a second driver and has a P-channel MOSFET 38. Vdd2 is applied to the source of the P-channel MOSFET 38, and the control signal 134 inverted by the inverter circuit 42 is input to the gate. Therefore, in the low voltage application circuit 32, the P-channel MOSFET 38 is turned on during the period when the control signal 134 is high, and outputs Vdd2.

  The turn-off circuit 33 has an N-channel MOSFET 39. The source of the N-channel MOSFET 39 is grounded, and the control signal 134 inverted by the inverter circuit 43 is input to the gate. Therefore, the turn-off circuit 33 outputs the ground level when the N-channel MOSFET 39 is turned on while the control signal is low.

  The backflow prevention diode 34 is connected between the drain of the P-channel MOSFET 36 and the drain of the P-channel MOSFET 38. Therefore, when the load current detection signal 135 is high and the control signal 134 is high, that is, during the period in which both the P-channel MOSFET 36 and the P-channel MOSFET 38 are on, the low voltage application circuit 31 The backflow of current to the voltage application circuit 32 is prevented.

  Next, the operation of the drive voltage switching circuit 70 according to the fifth embodiment will be described. Note that the timing chart is the same as that in FIG. 16 described in Embodiment 4.

  When a high level control signal 134 is input from the control circuit 21 to the drive voltage switching circuit 70, the inverter circuit 43 blocks the N-channel MOSFET 39 in the turn-off circuit 33, while the inverter circuit 42 causes the low voltage application circuit 32 to enter the drive voltage switching circuit 70. The P-channel MOSFET 38 becomes conductive, and the low power supply voltage Vdd2 is supplied as a drive voltage for the voltage-controlled switching element 25 via the backflow prevention diode 34, and the voltage-controlled switching element 25 is turned on. After the turn-on, the current flowing through the voltage-controlled switching element 25 increases. When the threshold value Idsth is exceeded, the load current detection circuit 135 is turned on by the load current detection circuit 27 and the output of the NAND circuit 41 is inverted. . The signal output by the level shift circuit 35 controls the P-channel MOSFET 36 on and off. That is, when the current flowing through the voltage control type switching element 25 exceeds the threshold value Idsth, Vdd1 is supplied as the drive voltage of the voltage control type switching element 25, and the high level of the drive signal 132 is switched from Vdd2 to Vdd1.

  In addition, since a backflow prevention diode 34 is inserted between the high voltage application circuit 31 and the low voltage application circuit 32, no current flows back through the low voltage application circuit 32. In addition, a constant current circuit 37 is connected to the source of the P-channel MOSFET in the high voltage application circuit 31, and the gate charge current for switching the drive voltage is supplied at a constant current, so the constant current circuit 37 is inserted. The rise of the drive signal 132 to Vdd1 becomes gradual compared to the case where it is not done.

  Thus, when the load current is larger than Idsth, the load current detection circuit 27 and the NAND circuit 41 generate a pulse for enabling the output of the high voltage application circuit 31, and the high voltage application circuit 31 has Vdd1 as a source. Is applied, and a pulse signal obtained by taking the logical product of the load current detection signal 135 and the control signal 134 is applied to the gate, and the low voltage application circuit 32 applies Vdd2 to the source, Includes a P-channel MOSFET 38 to which a control signal 134 indicating a period during which the voltage-controlled switching element 25 is turned on and a period during which the voltage-controlled switching element 25 is turned off is applied, and the drive voltage switching circuit 70 includes a drain of the P-channel MOSFET 36, Prevents backflow of current connected between the drain of MOSFET38 And preventing diode 34 flow, and a N-channel MOSFET39 complementarily turned on or off and P-channel MOSFET 38, it is applied to the voltage-controlled switching device 25 of the drain voltage of the P-channel MOSFET36 as the drive signal 132.

  Thereby, the drive voltage switching circuit 70 according to the fifth embodiment can be easily configured by using the MOSFET.

  As mentioned above, although demonstrated based on embodiment, this invention is not limited to this embodiment. Unless it deviates from the meaning of this invention, the form which carried out the various deformation | transformation which those skilled in the art can think to this embodiment, and the structure constructed | assembled combining the component in different embodiment is also contained in the scope of the present invention. .

  For example, the load current detection circuit 27 may output an analog signal corresponding to the load current, and may process the analog signal in the drive voltage switching circuit 22 or the control circuit 21.

  10, FIG. 11, FIG. 13 and FIG. 17, the load current is detected from the high voltage side of the voltage control type switching element 25, but a signal is inserted into the low voltage side and subjected to IV conversion. May be input to the load current detection circuit 27.

  The present invention is a drive circuit that drives a power switching element in a switching power supply, and is specifically suitable for a switching power supply used in a liquid crystal television, a plasma television, a DVD recorder, and the like.

1 is a diagram illustrating a configuration of a switching power supply device including a drive circuit according to a first embodiment. FIG. 3 is a diagram illustrating a configuration of a drive circuit, a voltage control switching element, and a feedback circuit according to the first embodiment. It is a block diagram which shows a more detailed structure. It is a figure which shows the relationship between the load connected to a switching power supply device, and the sum of the drive loss which is main loss, conduction | electrical_connection loss, and switching loss. It is a figure which shows the magnitude | size of each loss in the stand-by state shown in FIG. 4, and a rated load state. It is a graph which shows the VI characteristic of power MOSFET. 5 is a timing chart showing a power supply output current and a power supply output voltage of the switching power supply device according to the present embodiment, and a drain current and a gate voltage of a voltage controlled switching element with respect to different load states. It is a circuit diagram which shows the equivalent circuit of the device which combines MOSFET and IGBT. It is a graph which shows the VI characteristic of the device which combined MOSFET and IGBT. It is a figure which shows the structure provided with the ammeter instead of the feedback circuit. It is a schematic diagram which shows the more detailed structure provided with the ammeter instead of the feedback circuit. 6 is a timing chart showing a power supply output current and a power supply output voltage in each load state, and a drain current and a gate voltage of a voltage-controlled switching element in a switching power supply device including the drive circuit according to the second embodiment. It is a figure which shows the structure of the drive circuit which concerns on this Embodiment 3, a voltage control type switching element, and an ammeter. 10 is a timing chart showing an operation in a normal state and an overcurrent state of the drive circuit according to the third embodiment. It is a figure which shows the structure of the drive circuit which concerns on this Embodiment 4, a voltage control type switching element, and a feedback circuit. 5 is a timing chart showing a power supply output current and a power supply output voltage of the switching power supply device according to the present embodiment, and a drain current and a gate voltage of a voltage controlled switching element with respect to different load states. It is a figure which shows the structure provided with the ammeter instead of the feedback circuit of this Embodiment 4. FIG. 10 is a circuit diagram of a drive voltage switching circuit provided in a drive circuit according to a fifth embodiment. It is a figure which shows an example of a structure of a switching power supply device. It is a timing chart which shows the power supply output current and power supply output voltage of the conventional switching power supply apparatus with respect to different load states, and the drain current and gate voltage of a voltage control type switching element.

Explanation of symbols

SW1 1st switch SW2 2nd switch 2 Gate voltage switching circuit 3 High voltage driver 4 Low voltage driver 10, 37 Constant current circuit 20, 50, 60, 108 Driving circuit 21 Control circuit 22, 70 Driving voltage switching circuit 25 Voltage control type Switching element 26 Ammeter 27 Load current detection circuit 31 High voltage application circuit 32 Low voltage application circuit 33 Turn-off circuit 34 Backflow prevention diode 35 Level shift circuit 36, 38 P-channel MOSFET
39 N-channel MOSFET
41 NAND circuit 42, 43 Inverter circuit 51 Disable circuit 52 Overcurrent protection circuit 53 Delay circuit 54 AND gate 55 Overcurrent detection signal 80 Equivalent circuit 81 Unipolar transistor 83 Bipolar transistor 100, 200 Switching power supply device 101 Primary side rectifying / smoothing circuit 102 Switching circuit 103 Transformer 104 Secondary side rectifying / smoothing circuit 105, 106 Input terminal 109 Diode bridge 110 Input capacitor 111 Primary winding 112 Secondary winding 113 Rectifier diode 114 Choke coil 115 First output capacitor 116 Second output capacitor 117 , 118 Output terminal 119 Feedback circuit 120 Auxiliary winding 121 External resistor of drive circuit 122 Resonance capacitor 132 Drive signal 133 Feedback Control signal 134 control signal 135 load current detection signal 141 load current signal

Claims (13)

A drive circuit for driving a power switching element in a switching power supply device,
Generating means for generating a driving signal for turning on and off the power switching element, the driving signal having a plurality of levels of voltages for turning on the power switching element;
Switching control means for switching the voltage of the plurality of levels to turn on the power switching element according to the state of the power switching element ,
The multi-level voltage includes a first voltage and a second voltage lower than the first voltage;
The generating means includes a first driver that generates the first voltage, and a second driver that generates the second voltage,
The switching control means includes the first driver and the second driver so that a level of the second voltage pulse is generated as the drive signal to be turned on when the load current is equal to or less than a first threshold value. Control
When the load current is larger than the first threshold value, the first driver and the second driver are set so that the level of the drive signal to be turned on is a pulse of the first voltage.
A drive circuit that controls the device . The drive circuit according to claim 1, wherein the switching control unit switches the voltages at the plurality of levels so that the voltage increases as the load current flowing through the power switching element increases. The generating means further said first driver and a driving circuit according to claim 1, further comprising a current limiting means for limiting the power current supplied to at least one of the second driver. The drive circuit further includes:
An overcurrent protection circuit that detects whether or not the load current is greater than the first threshold value and exceeds a second threshold value indicating an overcurrent reference, and stops the drive circuit when detected; ,
The drive circuit according to claim 3 , further comprising: a disable circuit that disables the first driver for a period corresponding to a period from when an overcurrent is detected to when the overcurrent is stopped. The switching control means generates a first control pulse signal for enabling the output of the first driver when the load current is larger than the first threshold;
The second driver generates a pulse of the second voltage level according to a second control pulse signal indicating a period for turning on and off the power switching element;
The disable circuit is
A delay circuit for delaying the second control pulse signal for a predetermined time;
The drive circuit according to claim 4 , further comprising: a gate circuit that outputs a logical product of the delayed second control pulse signal and the first control pulse signal to the first driver. The switching control means includes
Controlling the second driver to generate a pulse of the second voltage at a level as the drive signal to be turned on when the load current is less than or equal to the first threshold;
As the drive signal to be turned on when the load current is larger than the first threshold value,
Level so that to produce a further two-stage pulse rising to the first voltage rising to the second voltage, the driving circuit according to claim 1, wherein controlling the first driver and the second driver. The drive circuit according to claim 6 , wherein the generation unit further includes a current limiting unit that limits a power supply current supplied to at least one of the first driver and the second driver. The switching control means generates a first control pulse signal for enabling the output of the first driver when the load current is larger than the first threshold;
The first driver includes a first transistor in which the first voltage is applied to a source and a pulse signal obtained by ANDing the first control pulse signal and the second control pulse signal is applied to a gate. ,
The second driver includes a second transistor to which the second voltage is applied to a source and the second control pulse signal indicating a period for turning on and off the power switching element is applied to a gate. ,
The generation means further includes a backflow prevention diode connected between the drain of the first transistor and the drain of the second transistor to prevent backflow of current;
A third transistor that complementarily turns on or off with the second transistor;
Wherein a drain of the first transistor, and the cathode of the blocking diode, the third transistor drive circuit according to claim 1, wherein the drain and are connected to. A driving method for driving a power switching element in a switching power supply device,
The power switching element is turned on at a plurality of levels of voltage including a first voltage and a second voltage lower than the first voltage;
The driving method is:
Comparing the load current flowing through the power switching element with a threshold value;
When the load current is greater than the threshold value, the first driver and said by controlling the second driver for generating a second voltage, the ON signal pulses before Symbol first voltage to generate the first voltage To supply to the power switching element,
When the load current is below the threshold value, by controlling the first driver and the second driver, the pulse before Symbol second voltage as an ON signal, the driving method supplied to the power switching element. A diode bridge for rectifying the input AC signal;
A power switching element that switches the rectified voltage;
A drive circuit for driving the power switching element;
A transformer that receives the voltage generated by driving and converts it to a different voltage;
A rectifying and smoothing circuit that rectifies and smoothes the converted voltage and outputs the rectified voltage,
The drive circuit is
Generating means for generating a driving signal for turning on and off the power switching element, the driving signal having a plurality of levels of voltages for turning on the power switching element;
Switching control means for switching the voltage of the plurality of levels to turn on the power switching element according to the state of the power switching element ,
The multi-level voltage includes a first voltage and a second voltage lower than the first voltage;
The generating means includes a first driver that generates the first voltage, and a second driver that generates the second voltage,
The switching control means includes the first driver and the second driver so that a level of the second voltage pulse is generated as the drive signal to be turned on when the load current is equal to or less than a first threshold value. Control
When the load current is larger than the first threshold value, the first driver and the second driver are set so that the level of the drive signal to be turned on is a pulse of the first voltage.
Switching power supply that controls the device. The switching power supply device according to claim 10 , wherein the switching element is a unipolar transistor. The switching power supply device according to claim 10 , wherein the switching element is a transistor having a function of switching between a unipolar operation and a bipolar operation in accordance with a load current flowing through the switching element. The switching power supply device further includes:
A measuring unit for measuring a current output from the rectifying and smoothing circuit;
A conversion unit that converts the measured current into a load current flowing through the power switching element;
The switching power supply according to claim 10 , wherein the switching control unit switches the plurality of levels of voltages for turning on the power switching element according to the converted load current.

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