JP2012114558A - Drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensively configured drive circuit with less power supply components.SOLUTION: The drive circuit includes: a transformer DT1 having a primary winding Np and two or more secondary windings, including a first secondary winding S1 and a second secondary winding having the opposite polarity to the first secondary winding, and receiving a drive signal at the primary winding; a first switching element Qh on/off-controlled by a signal from the first secondary winding; a second switching element Ql on/off-controlled by a signal from the second secondary winding; first drive sections Q11, Q12 each connected between one end of the first secondary winding and a control terminal of the first switching element to drive the first switching element; second drive sections Q21, Q22 each connected between one end of the second secondary winding and a control terminal of the second switching element to drive the second switching element; voltage doubling rectification/smoothing circuits D11, D12, C11, C12 for supplying a first secondary winding voltage subjected to voltage doubling rectification/smoothing to the first drive section; and voltage doubling rectification/smoothing circuits D21, D22, C21, C22 for supplying a second secondary winding voltage subjected to voltage doubling rectification/smoothing to the second drive section.

Description

  The present invention relates to a drive circuit that drives a switching element using a transformer.

  FIG. 4 is a circuit diagram showing an example of a conventional driving circuit. In FIG. 4, the pulse signal generated by the pulse generator P1 is supplied to the primary winding N1 of the transformer T2 via the resistor R1 and the capacitor C1. The pulse signal generated in the secondary winding N2 of the transformer T2 is applied to the switching element Q0 composed of a MOSFET via the resistor R2, and the switching element Q0 is driven on and off according to the pulse signal.

  Here, when the secondary winding N2 is directly connected to the switching element Q0, when the on-duty of the pulse signal is 50%, for example, the maximum value of the pulse signal exceeds the threshold value Vth of the switching element Q0. Element Q0 is turned on. However, if the on-duty of the pulse signal changes more than 50%, the signal transmission waveform between the primary and secondary windings of the transformer T2 becomes a transmission waveform of only the AC signal, and therefore the pulse width is large. When the maximum value of the pulse signal decreases in proportion to and the maximum value of the pulse signal becomes less than the threshold value Vth of the switching element Q0, the switching element Q0 does not turn on. That is, when the on-duty changes, the drive voltage consisting of the pulse signal changes.

  The drive circuit described in Patent Document 1 solves the above problems. FIG. 5 shows an example of the drive circuit of Patent Document 1, and FIG. 6 shows the operation waveform of the drive circuit of Patent Document 1. In this drive circuit, when the on-duty of the drive signal Vs from the control unit 112 increases, the voltage Vc13 from the DC power supply Vcc applied to the primary winding nN1 of the transformer via the transistors Q11 and Q12 increases, and the secondary winding The voltage VT2 on line nN2 also increases. That is, since the maximum value of the voltage VT2 of the secondary winding nN2 is kept constant, the switching element Q can be easily driven.

JP 2001-345194 A

  However, in the drive circuit shown in FIG. 5, in order to detect the duty generated from the drive signal Vs and increase the second drive power supply voltage, 2 of the first drive power supply voltage and the second drive power supply voltage. Two drive power supply voltages were required. For this reason, the number of power supply parts has increased and the price has become high.

  In addition, when driven by a single power supply with only the second drive power supply voltage, the gate voltage applied to the switching element Q becomes high, exceeds the rated voltage of the gate voltage, and a margin cannot be taken from the viewpoint of reliability. It was not preferable.

  An object of the present invention is to provide an inexpensive driving circuit with reduced power supply components.

 In order to solve the above problems, a drive circuit of the present invention includes a primary winding, a second secondary winding having a polarity opposite to that of the first secondary winding and the first secondary winding. A transformer having two or more secondary windings having a line, a drive signal being applied to the primary winding, and a first output controlled by a signal output from the first secondary winding of the transformer One switching element, a second switching element that is controlled to be turned on and off by a signal output from the second secondary winding of the transformer, one end of the first secondary winding of the transformer, and the first switching element A first driving unit connected between the control terminal and driving the first switching element; and connected between one end of the second secondary winding of the transformer and the control terminal of the second switching element. A second drive unit for driving the second switching element; A first voltage doubler rectifying / smoothing circuit for voltage doubler rectifying and smoothing the first secondary winding voltage of the transformer and supplying the voltage doubler rectified smoothing voltage to the first drive unit; and a second secondary winding voltage of the transformer And a second voltage rectifying / smoothing circuit for supplying a voltage doubled rectified and smoothed voltage to the second drive unit.

 According to the present invention, since the switching element Q can be driven by one driving power supply voltage, the power supply components are reduced and the cost is reduced. Each voltage doubler rectifying and smoothing circuit doubles the first and second secondary winding voltages of the transformer by double voltage rectifying and smoothing, and supplies the voltage doubled rectified and smoothed voltage to the first and second drive units. A constant voltage is supplied to the two driving units. Therefore, even if the gate pulse width of either the first switching element or the second switching element approaches 100%, a voltage capable of driving the gate of each switching element can be obtained, so that malfunction can be prevented.

FIG. 3 is a configuration diagram of a drive circuit according to the first embodiment. FIG. 6 is a diagram illustrating operation waveforms of the drive circuit according to the first embodiment. FIG. 5 is a diagram illustrating a waveform in which dead time of each switching element of the drive circuit according to the first embodiment is adjusted. It is a block diagram which shows an example of the conventional drive circuit. It is a block diagram which shows another example of the conventional drive circuit. It is a figure which shows the operation | movement waveform of the conventional drive circuit shown in FIG.

  Hereinafter, a drive circuit according to an embodiment of the present invention will be described in detail with reference to the drawings.

 1 is a configuration diagram of a drive circuit according to a first embodiment of the present invention. In the drive circuit shown in FIG. 1, a first switching element Qh made of an N-type MOSFET and a second switching element Ql made of an N-type MOSFET are connected in series. The drain of the first switching element Qh is connected to the positive electrode of the power supply (not shown), and a load (not shown) is connected between the connection point VS between the first switching element Qh and the second switching element Ql and the ground of the power supply (not shown). ing.

 The drive circuit 1 is connected as a gate drive circuit to the gate of the first switching element Qh and the gate of the second switching element Ql, and uses the first switching element Qh and the second switching element Ql as a pulse signal of the pulse generator Si. In response to the on / off drive, power is supplied to a load (not shown).

 In the drive circuit 1 shown in FIG. 1, a P-type MOSFET Q1 and an N-type MOSFET Q2, and a P-type MOSFET Q3 and an N-type MOSFET Q4 are connected in series between terminals of the drive circuit power supply Vcc.

 The output terminal of the pulse generator Si is connected to the gate of the P-type MOSFET Q3 and the gate of the N-type MOSFET Q4, and to the input terminal of the inverter INV1. The gate of the P-type MOSFET Q1 and the gate of the N-type MOSFET Q2 are connected to the output terminal of the inverter INV1.

 The drain of the P-type MOSFET Q1 and the drain of the N-type MOSFET Q2 are connected to one end (dot (●) terminal) of the primary winding P1 of the drive transformer DT1 via the capacitor C1, and the other end of the primary winding Np of the drive transformer DT1. Is connected to the drain of the P-type MOSFET Q3 and the drain of the N-type MOSFET Q4.

 A pulse voltage is applied to the primary winding Np of the drive transformer DT1 when the P-type MOSFET Q1 and the N-type MOSFET Q4 are simultaneously turned on or the P-type MOSFET Q3 and the N-type MOSFET Q2 are simultaneously turned on by the pulse signal of the pulse generator Si. It has become so.

 The dot (●) terminal of the first secondary winding S1 of the drive transformer DT1 is connected to the anode of the diode D11 and the cathode of the diode D12, and a capacitor is connected between the cathode of the diode D11 and the anode of the diode D12. C11 and C12 are connected in series, and the other end of the first secondary winding S1 of the drive transformer DT1 is connected to the connection point of the capacitors C11 and C12.

 The cathode of the diode D11 and one end of the capacitor C11 are connected to the source of the P-type MOSFET Q11, and the drain of the P-type MOSFET Q11 is connected to the drain of the N-type MOSFET Q12 via the resistor R11. The source of the N-type MOSFET Q12 is connected to a connection point between one end of the capacitor C12 and the anode of the diode D12. That is, the series circuit of the capacitors C11 and C12 is connected in parallel to the series circuit of the MOSFETs Q11 and Q12 and the resistor R11.

 The first secondary winding S1, the diodes D11 and D12, the capacitors C11 and C12, the resistor R11, and the MOSFETs Q11 and Q12 of the drive transformer DT1 constitute a high-side drive unit for the switching element Qh on the high side. Further, the diodes D11 and D12 and the capacitors C11 and C12 constitute a first voltage doubler rectifying and smoothing circuit. MOSFETs Q11 and Q12 constitute a first drive unit.

 The gate of the MOSFET Q11 and the gate of the MOSFET Q12 are connected to the dot (●) terminal of the first secondary winding S1 of the drive transformer DT1. The drain of MOSFET Q11 is connected to resistor R11, and the drain of MOSFET Q12 is directly connected to the gate of switching element Qh.

 The dot (●) terminal of the second secondary winding S2 of the drive transformer DT1 has a polarity opposite to that of the secondary winding S1. That is, the anode of the diode D21 and the cathode of the diode D22 are connected to the other end of the second secondary winding S2 of the drive transformer DT1, and capacitors C21 and C22 are connected in series between the cathode of the diode D21 and the anode of the diode D22. It is connected to the. The connection point of the capacitors C21 and C22 is connected to the dot (●) terminal of the second secondary winding S2 of the drive transformer DT1.

 The cathode of the diode D21 and one end of the capacitor C21 are connected to the source of the P-type MOSFET Q21, the drain of the P-type MOSFET Q21 is connected to the drain of the N-type MOSFET Q22 via the resistor R21, and the source of the N-type MOSFET Q22 is connected to one end of the capacitor C22. The diode D22 is connected to the connection point with the anode. That is, the series circuit of the capacitors C21 and C22 is connected in parallel to the series circuit of the MOSFETs Q21 and Q22 and the resistor R21.

 The gate of the MOSFET Q21 and the gate of the MOSFET Q22 are connected to the other end of the second secondary winding S2 of the drive transformer DT1. The drain of MOSFET Q21 is connected to resistor R21, and the drain of MOSFET Q22 is directly connected to the gate of switching element Ql.

 The second secondary winding S2, the diodes D21 and D22, the capacitors C21 and C22, the resistor R21, and the MOSFETs Q21 and Q22 of the drive transformer DT1 constitute a low-side drive unit of the switching element Ql provided on the low side. The diodes D21 and D22 and the capacitors C21 and C22 constitute a second voltage doubler rectifying and smoothing circuit. MOSFETs Q21 and Q22 constitute a second drive unit.

 FIG. 2 is a diagram illustrating operation waveforms of the drive circuit according to the first embodiment. In FIG. 2, the pulse signal of the pulse generator Si is converted from the state of time duty from time t2 to time t4 to the state of duty << 50% from the state of time duty from time t2 to time t4 >> The waveform of each part is shown when the duty returns to 50% from time t4.

 In FIG. 2, Si is a pulse signal of the pulse generator Si, VNP is a voltage across the primary winding Np of the drive transformer DT1, VS1 is a voltage across the first secondary winding S1, and VA is a first voltage of the drive transformer DT1. , Vgh is a gate voltage applied to the first switching element Qh, VS2 is a voltage across the second secondary winding S2, and VB is a drive transformer. The voltage at one end B (no dot ● side) of the second secondary winding S2 of DT1, Vc21 and Vc22 indicate the voltages of the capacitors C21 and C22, and Vgl indicates the gate voltage applied to the second switching element Ql. .

 Next, the operation of the drive circuit according to the first embodiment configured as described above will be described in detail with reference to FIG.

 First, in the period from time t1 to t2, the pulse signal of the pulse generator Si has a duty of 50%. In the period t11, the MOSFETs Q1 and Q4 are turned on by the H level of the pulse signal. Then, a current flows through a path of Vcc positive electrode → Q1 → C1 → Np → Q4 → Vcc negative electrode. Therefore, the positive voltage on the dot (●) terminal side is applied to the primary winding Np of the drive transformer DT1 via the capacitor C1, and the winding voltage VNP has the same phase as the signal of the pulse generator Si.

 Next, in the period t12, the MOSFETs Q1 and Q4 are turned off and the MOSFETs Q2 and Q3 are turned on by the L level of the pulse signal Si. Then, a current flows through a path of Vcc positive electrode → Q3 → Np → C1 → Q2 → Vcc negative electrode. For this reason, an antiphase pulse is applied to the primary winding Np of the drive transformer DT1.

 The pulse voltage VNP applied to the primary winding Np has a pulse waveform of ± polarity with respect to the ground potential g1 of the drive circuit power supply because the DC component is cut by the capacitor C1.

 Next, since the first secondary winding S1 of the drive transformer DT1 constituting the high-side drive unit has the same polarity as the primary winding Np, a pulse having the same phase is applied to the first secondary winding S1. A voltage VS1 is applied. The pulse voltage VS1 is subjected to voltage doubler rectification and smoothing by a voltage doubler rectification and smoothing circuit using diodes D11 and D12 and capacitors C11 and C12 to obtain a voltage doubler rectification and smoothing voltage. This voltage doubler rectified and smoothed voltage becomes a power supply voltage for the resistor R11 and MOSFETs Q11 and Q12 constituting the buffer and inverter of the high-side drive unit.

 The voltage VA at the dot terminal (●) of the first secondary winding S1 is applied to the gates of the MOSFETs Q11 and Q12, and drives the gate of the first switching element Qh via the MOSFETs Q11 and Q12. However, a pulse signal having a phase opposite to that of the pulse signal of the pulse generator Si is output to the first switching element Qh due to the inverter configuration of the MOSFETs Q11 and Q12.

 Next, in the period of time t2 to t4, the pulse signal of the pulse generator Si is inverted to the duty << 50%.

 In the period t13, the MOSFETs Q2 and Q3 are turned on by the L level of the pulse signal. Then, a current flows through a path of Vcc positive electrode → Q3 → Np → C1 → Q2 → Vcc negative electrode. For this reason, an antiphase pulse is applied to the primary winding Np of the drive transformer DT1.

 In the period t14, the MOSFETs Q2 and Q3 are turned off and the MOSFETs Q1 and Q4 are turned on by the L level of the pulse signal Si. Then, a current flows through a path of Vcc positive electrode → Q1 → Np → C1 → Q4 → Vcc negative electrode, and a pulse having the same phase is applied to the primary winding Np of the drive transformer DT1.

 At this time, the charge charged in the capacitor C1 is discharged and charged at time t2 to t3, and the polarity of the charge is reversed. Therefore, the primary winding voltage VNP of the drive transformer Dt1 becomes a potential during the period from time t3 to t4 while being affected by the charging voltage of the capacitor C1. Similarly, the pulse waveform of the first secondary winding S1 of the drive transformer DT1 also changes.

 Here, the dot (●) terminal voltage VA of the first secondary winding S1 of the drive transformer DT1 maintains a constant peak voltage with respect to the VS potential that is the ground of the high-side drive unit. That is, the other end of the first secondary winding S1 is connected to the middle point of the capacitors C11 and C12, and the series voltage of the potential Vc11 of the capacitor C11 and the potential Vc12 of the capacitor C12 is double-voltage rectified and smoothed. Since the combined voltage VCD of the potential Vc11 and the potential Vc12 is a constant voltage, the dot (●) terminal voltage VA is held at a constant voltage with respect to the VS potential that is the ground of the driving unit.

 Therefore, since the dot (●) terminal voltage VA held at a constant voltage is applied to the gates of the MOSFETs Q11 and Q12, the gate drive voltage Vgh of the first switching element Qh is the duty signal of the pulse generator Si. Even if the duty is changed from 50% to duty << 50%, a constant pulse voltage can be maintained.

 Similarly, in the low-side drive unit, only the polarity of the second secondary winding S2 of the drive transformer DT1 is inverted, and the gate drive voltage Vgl in phase with the pulse signal of the pulse generator Si is output.

  As described above, according to the driving circuit of the first embodiment, the switching elements Qh and Ql can be sufficiently driven using a single driving power supply voltage even when the on-duty of the pulse signal is maximum. A drive circuit having a simple structure can be provided.

 Each voltage doubler rectifying / smoothing circuit doubles the first and second secondary winding voltages of the drive transformer DT1 and rectifies and supplies the double voltage rectified smoothed voltage as a power source to the high-side drive unit and the low-side drive unit. In addition, a constant voltage is supplied to the high side driving unit and the low side driving unit. Therefore, even if the gate pulse width of either the first switching element Qh or the second switching element Ql approaches 100%, a voltage capable of driving the gates of the switching elements Qh and Ql can be obtained, so that malfunction can be prevented.

  Further, the drive transformer DT1 can be driven by one to drive the two switching elements Qh and Ql, and a drive circuit having a simpler and cheaper configuration can be provided.

 FIG. 3 is a diagram illustrating a waveform in which the dead time of each switching element of the drive circuit according to the first embodiment is adjusted. By adjusting the resistance values of the resistor R11 and the resistor R21 shown in FIG. 1, the gate voltages Vgh and Vgl applied to the gates of the first switching element Qh and the second switching element Ql are dead as shown in FIG. Times dt1 and dt2 are generated. Accordingly, it is possible to prevent the first switching element Qh and the second switching element Ql from being turned on simultaneously.

 The present invention is not limited to the drive circuit of the first embodiment described above. In the driving circuit of the first embodiment, the driving circuit of the half bridge circuit is illustrated, but, for example, a bridge configuration is formed by four switching elements, four secondary windings, two high-side driving units, and two low-side driving units. A drive circuit of a full bridge circuit may be configured.

 In the first embodiment, the resistor R11 is connected between the MOSFET Q11 and the MOSFET Qh, and the resistor R21 is connected between the MOSFET Q21 and the MOSFET Ql. For example, the resistor R11 is connected between the cathode of the diode D11 and one end of the capacitor C11. A connection point may be connected between the MOSFET Q11, and the resistor R21 may be connected between the connection point between the cathode of the diode D21 and one end of the capacitor C21 and the MOSFET Q21. Even in this case, the same effect as that of the driving circuit of the first embodiment can be obtained.

  The present invention is applicable to a power supply device.

Vcc drive circuit power supply 1 drive circuit Si pulse generator DT1 drive transformer Np primary winding S1 first secondary winding S2 second secondary winding Qh first switching element Ql second switching elements Q2, Q4, Q12 , Q22 N-type MOSFET
Q1, Q3, Q11, Q21 P-type MOSFET
D11, D12, D21, D22 Diode C1, C11, C12, C21, C22 Capacitor INV1 Inverter R11, R21 Resistance

Claims (3)

A primary winding; two or more secondary windings having a first secondary winding and a second secondary winding having a polarity opposite to the polarity of the first secondary winding; A transformer to which a drive signal is applied to the primary winding;
A first switching element that is on / off controlled by a signal output from the first secondary winding of the transformer;
A second switching element that is on / off controlled by a signal output from the second secondary winding of the transformer;
A first drive unit connected between one end of the first secondary winding of the transformer and a control terminal of the first switching element to drive the first switching element;
A second drive unit connected between one end of the second secondary winding of the transformer and a control terminal of the second switching element, and driving the second switching element;
A first voltage doubler rectifying / smoothing circuit for voltage doubler rectifying and smoothing the first secondary winding voltage of the transformer and supplying a voltage doubler rectified and smoothed voltage to the first drive unit;
A second voltage doubler rectifying and smoothing circuit for supplying a voltage doubler rectified and smoothed voltage to the second drive unit by rectifying and smoothing a second secondary winding voltage of the transformer;
A drive circuit comprising:   The first drive unit receives a voltage from one end of the first secondary winding of the transformer, and the second drive unit includes the two terminals of the second secondary winding of the transformer. 2. The drive circuit according to claim 1, wherein a voltage is input from a terminal having a polarity opposite to that of one end of the first secondary winding of the transformer. A first resistor connected between the first driving unit and a control terminal of the first switching element;
A second resistor connected between the second drive unit and a control terminal of the second switching element;
3. The drive circuit according to claim 1, wherein a dead time between the first switching element and the second switching element is generated by adjusting the first resistance and the second resistance.

Images