JP5905689B2 - DC / DC converter, power supply device using the same, and electronic device - Google Patents

Description

  The present invention relates to a DC / DC converter.

  Various home appliances such as TVs and refrigerators, or electronic devices such as laptop computers, mobile phone terminals and PDAs (Personal Digital Assistants) operate by receiving external power, and also from an external power source. The built-in battery can be charged with the power of In home appliances and electronic devices (hereinafter collectively referred to as electronic devices), a power supply device that converts commercial AC voltage into AC / DC (AC / DC) is built-in, or the power supply device is a power source external to the electronic device. Built in the adapter (AC adapter).

The power supply device includes a rectifier circuit (diode bridge circuit) that rectifies an AC voltage, and an insulating DC / DC converter that steps down the rectified voltage and supplies the voltage to a load.
FIG. 1 is a diagram showing a configuration of a DC / DC converter 100r examined by the present inventors. The specific configuration of the DC / DC converter 100r should not be regarded as a general technique well known to those skilled in the art.

In the DC / DC converter 100r, a DC input voltage _VIN from a rectifier circuit (not shown) provided in the preceding stage is input to the input terminal P1. The DC / DC converter 100r steps down the input voltage _VIN and supplies it to a load connected to the output terminal P2.

The DC / DC converter 100r mainly includes a switching transistor M1, a transformer T1, a first diode D1, a first output capacitor Co1, a control circuit 10r, and a feedback circuit 20r. In the DC / DC converter 100r, the primary side region and the secondary side region of the transformer T1 must be electrically insulated. The feedback circuit 20r includes resistors R1 and R2 that divide the output voltage _VOUT , a shunt regulator 22, and a photocoupler 24.

The shunt regulator 22 is an error amplifier that amplifies an error between the _divided output voltage V _OUT ′ and the reference voltage V _REF corresponding to the target value of the output voltage V _OUT . The photocoupler 24 feeds back a feedback signal corresponding to the error between the output voltage _VOUT and the target voltage to the control circuit 10r. The control circuit 10r controls the on / off duty ratio of the switching transistor M1 by pulse modulation so that the output voltage _VOUT matches the target value.

Control circuit 10r is where is operable at about 10V supply voltage _{V CC,} it is driven with an input voltage _V IN (about 140 V) so the efficiency is deteriorated. On the other hand, since the voltage V _OUT stepped down by the DC / DC converter 100r is generated on the secondary side of the transformer T1, the voltage V _OUT cannot be supplied to the control circuit 10r provided on the primary side.

Therefore, an auxiliary coil L3 is provided on the primary side of the transformer T1. Auxiliary coil L3, a second diode D2 and the second output capacitor Co2 serves as an auxiliary DC / DC converter for generating a supply voltage _{V CC} for the control circuit 10r. In the DC / DC converter 100r, power supply voltage _{V CC} is proportional to the output voltage _{V OUT,} the proportionality coefficient is determined by the winding ratio of the secondary coil L2 and the auxiliary coil L3 of the transformer T1.
V _CC = V _OUT × N _D / N _S
Here, _{N S} is the number of turns in the secondary coil L2, _{N D} is the number of turns of the auxiliary coil L3.

JP-A-9-098571 Japanese Patent Laid-Open No. 2-211055

  The present inventors have studied such a DC / DC converter 100r and have recognized the following problems. For example, consider a case where the DC / DC converter 100r is mounted on a television. Currently, the power consumption in the standby state of the television is required to be suppressed to 0.3 W or less. In the future, it is required to further reduce the power consumption, for example, 0.1 W or less, specifically about 50 mW.

Even in the standby state, it is necessary to supply a stable power supply voltage _VOUT to the microcomputer. Therefore, in the configuration of FIG. 1, the shunt regulator 22 operates even in the standby state. Current _{I 1} of the shunt regulator 22 is 1mA in this case, when the power supply voltage _{V OUT} is to 19V, the power consumption 19mW, and the one of the DC / DC converter 100r target 50mW of overall power consumption, occupy a large proportion become.

  An aspect of the present invention has been made in view of such problems, and one of exemplary purposes thereof is to provide a DC / DC converter that reduces power consumption in a standby state.

  An embodiment of the present invention relates to a DC / DC converter that transforms an input voltage and outputs an output voltage from an output terminal. This DC / DC converter has a primary coil, a secondary coil, and a transformer having an auxiliary coil provided on the primary coil side, and the potential of the first electrode is fixed, and the second electrode is connected to the output terminal. The first output capacitor, the first diode provided between the output terminal and the first terminal of the secondary coil with the cathode facing the output terminal, and the path of the primary coil are provided. The switching transistor, the second output capacitor with the potential of the first electrode fixed, the second electrode of the second output capacitor and the first terminal of the auxiliary coil, the cathode of the second output capacitor side A rectifying element provided in a direction, an operating state in the normal mode, and a non-operating state in the standby mode, and a first feedback signal corresponding to the output voltage is sent to the first photocoupler. A first feedback circuit for transmitting from the secondary side of the transformer to the primary side via the first, a non-operating state in the normal mode, an operating state in the standby mode, and a second feedback signal corresponding to the voltage generated in the second output capacitor A second feedback circuit to be generated, a voltage generated at the second output capacitor at the power supply terminal, a first feedback signal and a second feedback signal at the feedback terminal, and switching based on the signal input to the feedback terminal And a control circuit for controlling on / off of the transistor.

  According to this aspect, in the normal mode, the output voltage is stabilized at the first level based on the first feedback signal corresponding to the output voltage. In the standby mode, the first feedback circuit is stopped, and the output voltage is stabilized at the second level based on the second feedback signal corresponding to the voltage of the second output capacitor generated on the primary side of the transformer. The By designing the power consumption of the second feedback circuit in the standby mode to be smaller than the power consumption of the first feedback circuit in the normal mode, the power consumption in the standby mode can be reduced as compared with the conventional case.

The first feedback circuit is provided with a first resistor and a second resistor provided in series between the output terminal and the ground terminal, in a direction in which the cathode is on the output terminal side and the anode is on the ground terminal side, and A shunt regulator in which an output voltage divided by the first resistor and the second resistor is input to the reference terminal. The shunt regulator may be configured to turn off when the output voltage of the DC / DC converter is at the second level.
A voltage obtained by dividing the output voltage by the voltage dividing ratio K is input to the reference terminal of the shunt regulator. If the shunt regulator is turned off when the voltage at its reference terminal is lower than the predetermined level VTH1, the shunt regulator is automatically turned off in the standby mode by setting the second level to VTH1 / K or less. And the first feedback circuit can be deactivated.

The first feedback circuit may further include a first switch provided in series with the first and second resistors between the output terminal and the ground terminal. The first switch may be turned off in the standby mode.
In this case, in the standby mode, the current flowing through the first and second resistors can be cut off, so that the power consumption can be further reduced.

The first feedback circuit may include a first switch provided between the output terminal and the ground terminal. The first feedback circuit may be in a non-operating state by turning off the first switch in the standby mode.
By turning off the first switch, the current path can be cut off and the power consumption can be reduced.

The second feedback circuit may include a second switch provided between the second electrode of the second output capacitor and the ground terminal, and may be inactivated by turning off the second switch in the normal mode.
By turning off the second switch, the current path can be cut off and the power consumption can be reduced.

  The second feedback circuit responds to the voltage drop of the third resistor between the diode, the third resistor and the second switch provided in series between the second electrode of the second output capacitor and the ground terminal, and the base emitter. And a bipolar transistor to which a voltage is applied. The second feedback signal depends on the collector voltage of the bipolar transistor, and the second switch may be configured to be turned off in the normal mode.

The second feedback circuit is provided in series between the second electrode of the second output capacitor and the ground terminal, and generates a detection voltage corresponding to the voltage of the second electrode of the second output capacitor, and a second A switch and an error amplifier for amplifying an error between the detection voltage and a predetermined reference voltage may be included. The second switch may be configured to be turned off in the normal mode. The control circuit includes an output voltage of the error amplifier and a current detection comparator that compares a current detection signal corresponding to the current flowing through the switching transistor, and is configured to control the switching transistor according to the output signal of the current detection comparator May be.
In this case, the second feedback circuit may be incorporated in the control circuit.

  The second feedback circuit is provided in series between the second electrode of the second output capacitor and the ground terminal, and generates a detection voltage corresponding to the voltage of the second electrode of the second output capacitor, and a second A switch and an amplifier that receives the detection voltage and receives the second feedback signal may be included. The second switch may be configured to be turned off in the normal mode. The control circuit may include a burst comparator that compares the second feedback signal with a predetermined reference voltage. The control circuit may be configured to alternately repeat a period in which the switching transistor switches and a period in which switching is stopped in accordance with the output signal of the burst comparator.

  The second feedback circuit is provided in series between the second electrode of the second output capacitor and the ground terminal, and generates a detection voltage corresponding to the voltage of the second electrode of the second output capacitor, and a second And a switch. The control circuit may include a burst comparator that compares the detection voltage with a predetermined reference voltage, and may be configured to control the switching transistor according to the output signal of the burst comparator.

  Switching between the standby mode and the normal mode may be controlled by the load of the present DC / DC converter. The load may be configured to be able to generate a control signal indicating a mode. The DC / DC converter may further include a second photocoupler that transmits a control signal from the load from the secondary side of the transformer to the primary side.

  Another aspect of the present invention relates to a power supply apparatus. The power supply apparatus includes: an AC / DC converter that converts a commercial AC voltage into a DC voltage; and the DC / DC converter according to any one of the above that receives the DC voltage and supplies a voltage obtained by stepping down the DC voltage to a load. .

  Another embodiment of the present invention relates to an electronic device. This electronic apparatus may include an AC / DC converter that converts commercial AC voltage into DC voltage, a microcomputer, and a DC / DC converter that receives the DC voltage and supplies a voltage obtained by stepping down the DC voltage to the microcomputer.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, power consumption in the standby state can be reduced.

It is a figure which shows the structure of the DC / DC converter which this inventor examined. It is a circuit diagram which shows the structure of the electronic device which concerns on embodiment. FIG. 3 is a circuit diagram illustrating a configuration example of a control circuit in FIG. 2. It is a circuit diagram which shows the modification of a 1st feedback circuit. FIGS. 5A and 5B are circuit diagrams showing another configuration example of the second feedback circuit and the control circuit.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are physically directly connected, or the member A and the member B are electrically connected to each other. Including the case of being indirectly connected through other members that do not substantially affect the state of connection, or do not impair the functions and effects achieved by the combination thereof.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

FIG. 2 is a circuit diagram illustrating a configuration of the electronic apparatus 1 according to the embodiment.
The electronic device 1 is, for example, a home appliance such as a television, a refrigerator, or an air conditioner, or a computer. The electronic device 1 includes a microcomputer 2, a signal processing circuit 4, a DC / DC converter 100, and a rectifier circuit 102. The electronic device 1 is divided into a primary side and a secondary side that are insulated from each other. Half of the rectifier circuit 102 and the DC / DC converter 100 are arranged on the primary side, and half of the DC / DC converter 100, the microcomputer 2 and the signal processing circuit 4 are arranged on the secondary side.

The rectifier circuit 102 is, for example, a diode rectifier circuit, receives an _AC voltage VAC such as a commercial AC voltage, full-wave rectifies it, and smoothes it by the capacitor C1 to generate a DC voltage V _DC (= V _IN ). When V _AC = 100V, V _DC = 144V.

The DC / DC converter 100 receives the direct-current input voltage _VIN at its input terminal P1, steps down the voltage, and outputs it from the output terminal P2. A PFC (Power Factor Correction) circuit (not shown) may be provided between the DC / DC converter 100 and the rectifier circuit 102. The output voltage _VOUT from the output terminal P2 is output to the microcomputer 2 and the signal processing circuit 4. The microcomputer 2 controls the entire electronic device 1 in an integrated manner. The signal processing circuit 4 is a block that performs specific signal processing, and examples thereof include an interface circuit that performs communication with an external device, an image processing circuit, an audio processing circuit, and the like. Needless to say, the actual electronic device 1 is provided with a plurality of signal processing circuits 4 according to their functions. The operation guarantee voltage of the microcomputer 2 is 6V, for example, and the operation guarantee voltage of the signal processing circuit 4 is 12V higher than that of the microcomputer 2.

  The electronic device 1 can be switched between a normal state (also referred to as a normal mode) and a standby state (also referred to as a standby mode). In the normal mode, the microcomputer 2 and the signal processing circuit 4 operate. In the normal mode, the microcomputer 2 and the signal processing circuit 4 operate, and in the standby mode, only the microcomputer 2 operates.

  In the present embodiment, the microcomputer 2 switches between the normal mode and the standby mode. Further, the microcomputer 2 generates a control signal STB (also referred to as an STB signal) indicating a mode. The control signal STB is asserted (high level) in the normal mode, and negated (low level) in the standby mode.

  The above is the overall configuration of the electronic device 1. Next, a DC / DC converter 100 that can be suitably used for such an electronic apparatus 1 will be described.

  The DC / DC converter 100 mainly includes a transformer T1, a first diode D1, a second diode D2, a first output capacitor Co1, a second output capacitor Co2, a switching transistor M1, a control circuit 10, a first feedback circuit 20, and a second feedback. A circuit 40 and a second photocoupler 30 are provided.

The transformer T1 has a primary coil L1, a secondary coil L2, and an auxiliary coil L3 provided on the primary coil side. The number of turns of the primary coil L1 of the number of turns of _N P, 2 coil L2 and _{N S.} The number of turns of the auxiliary coil L3 is N _D2 .

  The switching transistor M1, the primary coil L1, the secondary coil L2, the first diode D1, and the first output capacitor Co1 form a first converter (main converter). The potential of the first electrode of the first output capacitor Co1 is grounded and fixed, and the second electrode is connected to the output terminal P2. The first diode D1 is provided between the output terminal P2 and one end N2 of the secondary coil L2 so that the cathode is on the first output capacitor Co1 side. The other end of the secondary coil L2 is grounded and the potential is fixed.

  The switching transistor M1 is provided on the path of the primary coil L1. A switching signal OUT from the control circuit 10 is input to the gate of the switching transistor M1 through the resistor R10.

  The switching transistor M1, the primary coil L1, the auxiliary coil L3, the second diode D2, and the second output capacitor Co2 form a second converter (auxiliary converter).

  The potential of the first electrode of the second output capacitor Co2 is fixed. The second diode D2, which is a rectifying element, is provided between the second electrode of the second output capacitor Co2 and the first terminal of the auxiliary coil L3 so that the cathode is on the second output capacitor Co2 side.

The first feedback circuit 20 generates a first feedback signal (I _FB ) corresponding to the output voltage V _OUT, and sends the first feedback signal (I _FB1 ) from the secondary side of the transformer via the first photocoupler 24. Transmit to the primary side.

A voltage signal (also referred to as a first feedback signal) V _FB1 corresponding to the first feedback signal I _FB1 generated by the first feedback circuit 20 is input to the feedback terminal FB (second pin) of the control circuit 10. The capacitor C3 is provided for the purpose of phase compensation.

For example, the first feedback circuit 20 includes a shunt regulator 22, a first photocoupler 24, and a voltage dividing circuit 26.
The voltage dividing circuit 26 divides the output voltage _VOUT of the DC / DC converter 100 at a voltage dividing ratio K. The divided output voltage V _OUT ′ (= V _OUT × K) is input to the reference terminal REF of the shunt regulator 22. The anode (A) of the shunt regulator 22 is grounded, and its cathode (K) is connected to the output voltage P2 via the resistors R21 and R22. The shunt regulator 22 amplifies an error between the output voltage V _OUT ′ and a predetermined reference voltage V _REF and outputs a current I _FB corresponding to the error. The path of the output current I _FB of the shunt regulator 22, the input side of the light emitting diodes of the first photocoupler 24 is provided. The first photocoupler 24 outputs a first feedback signal V _FB1 corresponding to the error between the output voltage V _OUT ′ and the reference voltage V _REF to the FB terminal of the control circuit 10. The resistors R21 and R22 are provided to appropriately bias the light emitting diode of the first photocoupler 24.

The control circuit 10 receives the first feedback signal _VFB1 , generates a switching signal OUT whose duty ratio is adjusted so that the _divided output voltage V _OUT ′ matches the reference voltage V _REF, and sets the switching transistor M1. To drive.
When the voltage dividing ratio of the voltage dividing circuit 26 is K (= R2 / (R1 + R2)), the output voltage V _OUT is
V _OUT1 = V _REF / K (1)
It is stabilized to satisfy.

  The first feedback circuit 20 is in an operation state in the normal mode and in a non-operation state in the standby mode.

  A control signal STB generated by the microcomputer 2 according to the mode is input to the second photocoupler 30. The second photocoupler 30 transmits a control signal STB generated on the secondary side to the primary side. For example, the light emitting element on the input side of the second photocoupler 30 is biased by the resistor R30, and the current can be switched on and off by the transistor M3. A control signal STB is input to the gate of the transistor M3.

The second feedback circuit 40 is inoperative in the normal mode, an operational state in the standby mode, to generate a second feedback signal V _FB2 corresponding to the voltage V _CC generated in the second output capacitor Co2. The second feedback signal V _FB2 is also input to the feedback terminal FB of the control circuit 10.

  For example, the second feedback circuit 40 includes a diode D3, a third resistor R3, a base resistor Rb1, a second switch M22, and a bipolar transistor Q1. The diode D3, the third resistor R3, and the second switch M22 are sequentially provided in series between the second electrode of the second output capacitor Co2 and the ground terminal. The order of the second switch M22, the diode D3, and the resistor R3 may be switched.

  A voltage corresponding to the voltage drop of the third resistor R3 is applied between the base and emitter of the bipolar transistor Q1 via the base resistor Rb1.

The second feedback signal V _FB2 depends on the collector voltage of the bipolar transistor Q1. A control signal STB is input to the control terminal of the second switch M22 via the second photocoupler 30. The second switch M22 is turned off in the normal mode and turned on in the standby mode.

Focusing on the second feedback circuit 40, the collector voltage or the second feedback signal _{V FB2} of the bipolar transistor Q1, the voltage drop across the third resistor R3, stable to 0.7V around a base-emitter voltage Vbe of the bipolar transistor Q1 To be adjusted. When the reverse voltage (zener voltage) of the diode D3 is Vz, the voltage V _CC of the second output capacitor Co2 is adjusted so that V _CC = Vbe + Vz. That is, the level of the second feedback signal _{V FB2} of the second feedback circuit 40 generates is adjusted so that the voltage _{V CC} matches the target voltage Vbe + Vz, the second feedback circuit 40 functions as an error amplifier.

The configuration of the second feedback circuit 40 is not limited to that of FIG.
Regardless of how the second feedback circuit 40 is configured, on / off of the current path between the second electrode of the second output capacitor Co2 and the ground terminal is controlled according to the control signal STB. By providing the second switch M22, the second feedback circuit 40 can be switched between a non-operating state and an operating state.

Control circuit 10 to the power source terminal VCC (8 pin) receives the voltage _{V CC} generated in the second output capacitor Co2. Note that the DC voltage _VDC is supplied to the power supply terminal VCC of the control circuit 10 via the resistor R11 before the second converter operates normally.

Based on the signal input to the feedback terminal FB, specifically, the control circuit 10 generates the switching signal OUT based on the first feedback signal V _FB1 in the normal mode and on the second feedback signal V _FB2 in the standby mode. The switching transistor M1 is turned on and off. For example, the control circuit 10 adjusts the duty ratio of the switching signal OUT using pulse width modulation (PWM), pulse frequency modulation (PFM), or the like. A method for generating the switching signal OUT is not particularly limited.

In the normal mode, the output voltage V _OUT is stabilized at the first level (V _OUT1 = V _REF / K) so as to satisfy Expression (1).

In the standby mode, so as to coincide with the target voltage with the voltage V _CC of the second output capacitor Co2, on of the switching transistor M1, the duty ratio and the switching frequency of the off-controlled. When it is stabilized at the target voltage with the voltage _{V CC} of the second output capacitor Co2, the output voltage _{V OUT} of the output terminal P2 is stabilized in the second level _{V OUT2} corresponding to the voltage _{V CC.} The second level V _OUT2 is determined according to the turns ratio of the auxiliary coil L3 and the secondary coil L2, and the second level V _OUT2 is set lower than the first level V _OUT1 .

That is, as the control circuit 10, the output voltage _{V OUT} in the normal mode does not match the first level _{V OUT1,} the output voltage _{V OUT} in the standby mode matches the second level _{V OUT2} is lower than the first level _{V OUT1,} The on / off of the switching transistor M1 is controlled.

  Next, a specific configuration example of the control circuit 10 will be described. The configuration of the control circuit 10 is not particularly limited in the present invention.

For example, the control circuit 10 determines the output voltage V _OUT generated in the first output capacitor Co1, the current I _M1 flowing in the switching transistor M1 (primary coil L1), and the first level V _D1 generated in the tap TP of the auxiliary coil L3. A switching signal OUT is generated.

The detection resistor Rs is provided for detecting the current I _M1 flowing through the switching transistor M1. A voltage drop (detection signal) Vs generated in the detection resistor Rs is input to a current detection terminal (CS terminal: third pin) of the control circuit 10. Further, the voltage V _D1 of the tap TP of the auxiliary coil L3 of the control circuit 10 is input to the ZT terminal (first pin) through a low-pass filter including a resistor R4 and a capacitor C4.

  FIG. 3 is a circuit diagram showing a configuration example of the control circuit 10 of FIG. The control circuit 10 includes an off signal generation unit 52, an on signal generation unit 54, a drive unit 56, and a switch control unit 70.

  A pull-up resistor R12 is provided between the power supply terminal and the feedback terminal FB.

The off signal generation unit 52 includes a comparator that compares the detection signal Vs with the feedback signal _VFB, and generates an off signal Soff that defines the timing at which the switching transistor M1 is turned off. The off signal Soff generated by the off signal generation unit 52 is asserted when the current I _M1 flowing through the switching transistor M1 reaches a level corresponding to the feedback signal _VFB .

For example, when the output voltage V _OUT ′ becomes lower than the reference voltage V _REF , the feedback signal V _FB becomes higher, the timing at which the off signal Soff is asserted is delayed, and the ON period Ton of the switching transistor M1 becomes longer, resulting in output. Feedback is applied in the direction in which the voltage _VOUT increases. Conversely, when the output voltage V _OUT ′ becomes higher than the reference voltage V _REF , the feedback signal V _FB becomes lower, the timing at which the off signal Soff is asserted becomes earlier, and the on period Ton of the switching transistor M1 becomes shorter, and as a result The feedback is applied in the direction in which the output voltage _VOUT decreases.

The on signal generation unit 54 generates an on signal Son that is asserted after the off signal Soff is asserted. 3 includes a comparator that compares the potential V _D1 of the tap TP of the auxiliary coil L3 with a predetermined level Vth. The on signal generation unit 54 asserts the on signal Son when the potential V _{D1 of the} tap TP decreases to the predetermined level Vth.

When the switching transistor M1 is turned on, a current I _M1 flows through the primary coil L1, and energy is stored in the transformer T1. Thereafter, when the switching transistor M1 is turned off, the energy stored in the transformer T1 is released. The on-signal generator 54 can detect that the energy of the transformer T1 has been completely released by monitoring the voltage V _D1 generated in the auxiliary coil L3. When detecting the release of energy, the on signal generation unit 54 asserts the on signal Son to turn on the switching transistor M1 again.

The drive unit 56 turns on the switching transistor M1 when the on signal Son is asserted, and turns off the switching transistor M1 when the off signal Soff is asserted. The drive unit 56 includes a flip-flop 58, a pre-driver 60, and a driver 62. The flip-flop 58 receives an on signal Son and an off signal Soff at a set terminal and a reset terminal, respectively. The state of the flip-flop 58 changes according to the on signal Son and the off signal Soff. As a result, the duty ratio of the output signal Smod of the flip-flop 58 is modulated so that the output voltage _VOUT matches the target value _VREF . In FIG. 3, the high level of the drive signal Smod and the switching signal OUT is associated with the switching transistor M1 being on, and the low level is associated with the switching transistor M1 being off.

  The pre-driver 60 drives the driver 62 according to the output signal Smod of the flip-flop 58. A dead time is set for the output signals SH and SL of the pre-driver 60 so that the high-side transistor and the low-side transistor of the driver 62 are not turned on simultaneously. A switching signal OUT is output from the driver 62.

  The above is the configuration of the DC / DC converter 100. Next, the operation will be described separately for the normal mode and the standby mode.

1. Normal mode In the normal mode, the microcomputer 2 asserts (high level) the STB signal. At this time, the second switch M22 is turned off, the second feedback circuit 40 is deactivated, and its power consumption is substantially zero.

Then, the switching transistor M1 is switched based on the first feedback signal _VFB1 generated by the first feedback circuit 20, and the output voltage _VOUT is stabilized at the first level _VOUT1 .

2. Standby mode In the standby mode, the microcomputer 2 negates (low level) the STB signal. At this time, the second switch M22 is turned on, and the second feedback circuit 40 is activated. As a result, the second feedback signal _{V FB2} is generated such that the voltage _{V CC} of the second output capacitor Co2 is coincident with the predetermined level. As a result of the stabilization of the voltage _VCC , the output voltage _VOUT is stabilized at the second level _VOUT2 .

On the other hand, attention is focused on the first feedback circuit 20. The shunt regulator 22 is turned off when the voltage V _OUT ′ at the reference terminal REF is lower than a predetermined level VTH1. The second level V _OUT2 is set to VTH1 / K or less. Therefore, in the standby mode, V _OUT ′ <VTH1 is established, and the shunt regulator 22 is turned off. Thereby, the 1st feedback circuit 20 will be in a non-operating state. Since the current flowing from the cathode to the anode of the shunt regulator 22 becomes substantially zero, the power consumption of the first feedback circuit 20 becomes very small.

  The above is the operation of the DC / DC converter 100.

  The power consumption of the second feedback circuit 40 in the standby mode is designed to be smaller than the power consumption of the first feedback circuit 20 in the normal mode. Therefore, according to the DC / DC converter 100 of FIG. 2, the power consumption in the standby mode can be reduced compared to FIG.

The power consumption of the microcomputer 2, when given by the product of the operating current and the supply voltage V _OUT, by lowering the second level V _OUT2 of the power supply voltage V _OUT of the microcomputer 2 in the standby mode, the consumption of the microcomputer 2 Electric power can be reduced.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. is there. Hereinafter, such modifications will be described.

(First modification)
FIG. 4 is a circuit diagram showing a modification of the first feedback circuit. The first feedback circuit 20a in FIG. 4 further includes a first switch M21 in addition to the first feedback circuit 20 in FIG. The first switch M21 is provided in series with the first resistor R1 and the second resistor R2 between the output terminal P2 and the ground terminal. The order of the first switch M21 and the resistors R1 and R2 may be interchanged. The control signal STB is input to the control terminal of the first switch M21, and the first switch M21 is turned off in the standby mode and turned on in the normal mode.

  According to the modification of FIG. 4, the first switch M21 is turned off in the standby mode, the potential of the reference terminal REF of the shunt regulator 22 is substantially zero, and the shunt regulator 22 is turned off. Thereby, the consumption current of the path including the shunt regulator 22 becomes substantially zero.

  In the first feedback circuit 20 of FIG. 2, in the standby mode, a current flows through the voltage dividing circuit 26, and power is slightly consumed. On the other hand, in the first feedback circuit 20a of FIG. 4, the current consumption of the voltage dividing circuit 26 is substantially zero. That is, the power consumption of the entire first feedback circuit 20a can be further reduced as compared with the first feedback circuit 20 of FIG.

  FIGS. 5A and 5B are circuit diagrams showing another configuration example of the second feedback circuit and the control circuit. 5A and 5B, the second feedback circuit is built in the control circuit 10. Further, the control circuit 10 is provided with a standby terminal STB for receiving the control signal STB.

  The second feedback circuit 40a in FIG. 5A includes a voltage generation circuit 42, a second switch M22, and an error amplifier 44. The voltage generation circuit 42 and the second switch M22 are provided in series between the power supply terminal VCC connected to the second electrode of the second output capacitor Co2 and the ground terminal. The second switch M22 is turned on in the standby mode and turned off in the normal mode.

Voltage generation circuit 42 generates the detection voltage _{V CC} 'in accordance with the power supply voltage _{V CC} of the second electrode of the second output capacitor Co2. Voltage generating circuit 42 includes power divider circuit voltage V _CC dividing, or the level shift circuit such as a power supply voltage V _CC level shifting diodes, combinations thereof.

The error amplifier 44 amplifies an error between the detection voltage V _CC ′ and a predetermined reference voltage V _REF to generate a second feedback signal V _FB2 . The output terminal of the error amplifier 44 is connected to the feedback terminal FB.

  The third switch M23 is provided in series with the pull-up resistor R12 between the feedback terminal FB and the power supply terminal VCC. The control signal STB inverted by the inverter 48 is input to the gate of the third switch M23. The third switch M23 is turned on in the normal mode and turned off in the standby mode. The power consumption of the pull-up resistor R12 can be reduced by turning off the third switch M23 in the standby mode.

In the standby mode, the output voltage V _ERR of the error amplifier 44 is input to the comparator that is the off signal generation unit 52. The control circuit 10a controls switching of the switching transistor M1 based on the off signal Soff.

In the second feedback circuit 40b of FIG. 5B, the amplifier 46 receives the detection voltage V _CC ′ and generates a second feedback signal V _FB2 . The amplifier 46 may be a voltage follower, an inverting amplifier, or a non-inverting amplifier.

The burst comparator 70 is a hysteresis comparator, and compares the second feedback signal V _FB2 with a predetermined reference voltage V _REF to generate a burst signal S1. The pulse generator 72 generates a pulse signal S2 for switching the switching transistor M1. The pulse generator 72 may be a simple oscillator or a pulse modulator. The mask circuit 74 masks the pulse signal S2 with the burst signal S1. The drivers 60 and 62 in FIG. 3 drive the switching transistor M1 based on the pulse signal S2 ′ output from the mask circuit 74.

In the standby mode, the control circuit 10b in FIG. 5A switches the switching transistor M1 according to the pulse signal S2 during the period of V _FB2 <V _REF , and switches the switching transistor M1 during the period of V _FB2 > V _REF. Stop. That is, the period during which the switching transistor M1 is switched and the period during which the switching is stopped are intermittently repeated. As a result, the level of the output voltage V _FB2 is maintained while pulsating near the reference voltage V _REF .

  5A and 5B, since the second feedback circuit can be built in the control circuit, the number of parts can be reduced as compared with FIG.

  In the embodiment, the case where the shunt regulator (error amplifier) 22 is provided on the secondary side of the transformer T1 has been described. However, this error amplifier may be provided on the primary side, and further incorporated in the control circuit 10. May be.

  In the embodiment, the case where the load (microcomputer) on the secondary side of the transformer T1 is controlled in the mode has been described. However, the present invention is not limited thereto, and the circuit provided on the primary side controls the mode. May be. In this case, a control signal indicating the mode may be transmitted from the primary side to the secondary side by a photocoupler.

Those skilled in the art will appreciate that there are various types of control circuit 10 and that the configuration is not limited in the present invention.
For example, a timer circuit that measures a predetermined off time Toff may be used as the on signal generation unit 54 in FIG. 3 instead of the comparator. It is also possible to fix the off time Toff by estimating in advance the time required for energy release. In this case, the circuit can be simplified in exchange for the deterioration of energy efficiency. The timer circuit may be an oscillator that oscillates at a predetermined frequency.

  In the embodiment, the case where the DC / DC converter 100 is mounted on the electronic device 1 has been described. However, the present invention is not limited thereto, and can be applied to various power supply apparatuses. For example, the DC / DC converter 100 can be applied to an AC adapter that supplies power to an electronic device. Examples of the electronic device in this case include a laptop computer, a desktop computer, a mobile phone terminal, and a CD player, but are not particularly limited.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are allowed without departing from the spirit of the present invention.

P1 ... input terminal, P2 ... output terminal, Co1 ... first output capacitor, Co2 ... second output capacitor, D1 ... first diode, D2 ... second diode, T1 ... transformer, L1 ... primary coil, L2 ... secondary Coil, L3 ... auxiliary coil, M1 ... switching transistor, 100 ... DC / DC converter, 10 ... control circuit, 20 ... first feedback circuit, 22 ... shunt regulator, 24 ... first photocoupler, 26 ... voltage divider circuit, 30 2nd photocoupler, 40 ... 2nd feedback circuit, 42 ... voltage generation circuit, 44 ... error amplifier, 46 ... amplifier, 50 ... burst comparator, R1 ... 1st resistor, R2 ... 2nd resistor, R3 ... 3rd resistor DESCRIPTION OF SYMBOLS 1 ... Electronic device, 2 ... Microcomputer, 4 ... Signal processing circuit, 102 ... Rectifier circuit, M21 ... 1st switch, M22 ... 2nd switch M23 ... the third switch.

Claims (11)

A DC / DC converter that transforms an input voltage and outputs an output voltage from an output terminal,
A transformer having a primary coil, a secondary coil, and an auxiliary coil provided on the primary coil side;
A first output capacitor in which the potential of the first electrode is fixed and the second electrode is connected to the output terminal;
A first rectifying element provided between the output terminal and the first terminal of the secondary coil in a direction in which the cathode is on the output terminal side;
A switching transistor provided on a path of the primary coil;
A second output capacitor in which the potential of the first electrode is fixed;
A second rectifying element provided between the second electrode of the second output capacitor and the first terminal of the auxiliary coil in a direction in which the cathode is on the second output capacitor side;
A first feedback circuit that is in an operating state in a normal mode and in a non-operating state in a standby mode, and transmits a first feedback signal corresponding to the output voltage from the secondary side of the transformer to the primary side via the first photocoupler;
A second feedback circuit that is in a non-operating state in the normal mode, is in an operating state in the standby mode, and generates a second feedback signal according to a voltage generated in the second output capacitor;
A voltage generated in the second output capacitor is received at the power supply terminal, and the second feedback signal is applied to the second feedback signal in the standby mode so that the output voltage matches the first level based on the first feedback signal in the normal mode. A control circuit for controlling on / off of the switching transistor so that the output voltage matches a second level lower than the first level,
Bei to give a,
The second feedback circuit includes a switch provided between the second electrode of the second output capacitor and a ground terminal, and is turned off when the switch is turned off in the normal mode. DC / DC converter. The first feedback circuit includes:
A first resistor and a second resistor provided in series between the output terminal and the ground terminal;
A shunt regulator provided with a direction in which the cathode is on the output terminal side and an anode on the ground terminal side, and a voltage divided by the first resistor and the second resistor is input to the reference terminal;
The DC / DC converter according to claim 1, wherein the DC / DC converter is configured to be turned off when an output voltage of the DC / DC converter is at the second level. The first feedback circuit includes:
3. The method according to claim 2, further comprising a first switch provided in series with the first and second resistors between the output terminal and the ground terminal, wherein the first switch is turned off in the standby mode. The DC / DC converter described.   2. The DC / DC according to claim 1, wherein the first feedback circuit includes a first switch provided between the output terminal and a ground terminal, and the first switch is turned off in the standby mode. converter. The second feedback circuit includes:
Between the second electrode and the ground terminal of the second output capacitor, the switch in series with the provided diode, a third resistor,
A bipolar transistor to which a voltage corresponding to the voltage drop of the third resistor is applied between its base and emitter;
Hints, the second feedback signal, DC / DC converter according to any one of claims 1 to 4, wherein the benzalkonium not depending on the collector voltage of the bipolar transistor. Switching between the standby mode and the normal mode is controlled by a load of the DC / DC converter, and the load is configured to generate a control signal indicating the mode,
This DC / DC converter, the control signal from the load, to any one of claims 1 to 5, characterized by further comprising a second photo-coupler for transmitting from the secondary side of the transformer to the primary side The DC / DC converter described. The second feedback circuit includes:
Wherein provided in series with the switches, and the voltage generating circuitry for generating a detection voltage corresponding to the voltage of the second electrode of the second output capacitor between the second electrode and the ground terminal of the second output capacitor,
An error amplifier that generates the second feedback signal by amplifying an error between the detection voltage and a predetermined reference voltage;
Only including,
Before Symbol control circuit,
A current detection comparator that compares an output voltage of the error amplifier with a current detection signal corresponding to a current flowing through the switching transistor;
Hints, in response to said output signal of the current detecting comparator, DC / DC converter according to any one of claims 1 to 6, characterized in that it is configured to control the switching transistor. The second feedback circuit includes:
Between the second electrode and the ground terminal of the second output capacitor, the switch and arranged in series, the voltage generating circuits for generating a detection voltage corresponding to the voltage of the second electrode of the second output capacitor And
Receiving the detection voltage, and supplying the second feedback signal to an amplifier;
Only including,
The control circuit includes:
A burst comparator that compares the second feedback signal with a predetermined reference voltage is configured to alternately repeat a period in which the switching transistor is switched and a period in which switching is stopped according to the output signal of the burst comparator. The DC / DC converter according to any one of claims 1 to 6 , wherein: The control circuit includes a pull-up resistor and a third switch provided in series between a feedback terminal to which the first feedback signal is input and the power supply terminal,
The DC / DC converter according to claim 7 or 8 , wherein the third switch is turned off in the standby mode. An AC / DC converter that converts commercial AC voltage to DC voltage;
The DC / DC converter according to any one of claims 1 to 9 , wherein the DC / DC converter receives the DC voltage and supplies a voltage obtained by stepping down the DC voltage to a load.
A power supply apparatus comprising: An AC / DC converter that converts commercial AC voltage to DC voltage;
A microcomputer,
The DC / DC converter according to any one of claims 1 to 9 , wherein the DC voltage is received and the voltage obtained by stepping down the DC voltage is supplied to the microcomputer.
An electronic device comprising:

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