JP5640731B2 - Drive circuit and switching power supply device - Google Patents

Description

  The present invention relates to a drive circuit for driving a semiconductor switching element and a switching power supply device.

  FIG. 4 is a circuit diagram showing an example of a switching power supply device having a conventional drive circuit. In the switching power supply device shown in FIG. 4, a low-side normally-off switch Q1 made of a silicon (Si) device MOSFET and a high-side normally-off switch made of a silicon (Si) device MOSFET are provided at both ends of the DC power supply V1. A series circuit with Q2 is connected. A series circuit of the primary winding P1 of the transformer T1 and the resonance capacitor C2 is connected between the drain and source of the normally-off switch Q1.

  The diode D5 is connected in parallel to the normally-off switch Q2, and the diode D6 is connected in parallel to the normally-off switch Q1.

  The first secondary winding S1 and the second secondary winding S2 of the transformer T1 are connected in series, the anode of the diode D7 is connected to one end of the first secondary winding S1, and the second One end of the secondary winding S2 is connected to the anode of a diode D8. The cathode of the diode D7 and the cathode of the diode D8 are connected to one end of the capacitor C4 and one end (+ Vo) of the output terminal, and the other end of the capacitor C4 is connected to the other end (−Vo) of the output terminal and the first secondary winding. The other end of the line S1 and the other end of the second secondary winding S2 are connected. Diodes D7 and D8 and capacitor C4 constitute a full-wave rectifying and smoothing circuit.

  The first auxiliary winding P2 and the second auxiliary winding P3 of the transformer T1 are connected in series, the anode of the diode D3 is connected to one end of the first auxiliary winding P2, and the second auxiliary winding One end of P3 is connected to the anode of a diode D4. The cathode of the diode D3 and the cathode of the diode D4 are connected to one end of the capacitor C1, and the other end of the first auxiliary winding P2 and the other end of the second auxiliary winding P3 are connected to the other end of the capacitor C1 and a direct current. It is connected to the negative electrode of the power supply V1. The capacitor C1 constitutes a low side drive power supply supplied to the low side drive circuit LDRV.

  A starting resistor R0 is connected between the positive electrode of the DC power supply V1 and one end of the capacitor C1. The anode of the diode D9 is connected to the connection point between the starting resistor Ro and the capacitor C1, and the cathode of the diode D9 is connected to one end of the capacitor C3. The diode D9 and the capacitor C3 constitute a high side drive power supply supplied to the high side drive circuit HDRV.

  The voltage detection circuit 11 detects the output voltage of the capacitor C4 and outputs the detection voltage to the oscillator OSC as a feedback signal FB. The oscillator OSC compares the feedback signal FB and the triangular wave signal, thereby generating a pulse signal having a variable ON width in accordance with the feedback signal FB. The low side drive circuit LDRV turns on / off the normally-off type switch Q1 by a pulse signal from the oscillator OSC.

The level shift circuit LST inverts the pulse signal from the oscillator OSC by the inverter INV, converts the inverted pulse signal to a predetermined signal level, and supplies the signal to the high side drive circuit HDRV. The high side drive circuit HDRV turns on / off the normally-off type switch Q2 by the inverted pulse signal from the level shift circuit LST.

The level shift circuit LST includes an inverter INV, one-shot circuits OST1 and OST2 connected to the output of the inverter INV, a series circuit of a resistor R2, an FET Q4, and a resistor R4, and a series circuit of a resistor R3, an FET Q3, and a resistor R5. And a flip-flop circuit FF1 having a set terminal S connected to one end of the resistor R3 and a reset terminal R connected to one end of the resistor R2, and diodes D1 and D2.

The one-shot circuit OST1 generates a one-shot pulse at the rising edge of the inverted pulse signal from the inverter INV. The FET Q3 is turned on by a one-shot pulse from the one-shot circuit OST1, and outputs a set signal to the set terminal S of the flip-flop circuit FF1.

The one-shot circuit OST2 generates a one-shot pulse at the falling edge of the inverted pulse signal from the inverter INV. The FET Q4 is turned on by a one-shot pulse from the one-shot circuit OST2, and outputs a reset signal to the reset terminal R of the flip-flop circuit FF1. The output terminal Q of the flip-flop circuit FF1 is connected to the high side drive circuit HDRV and outputs an inverted pulse signal converted to a predetermined signal level.

  In addition, the power supply system described in patent document 1 is known as a prior art.

JP 2006-223016 A

  However, in the drive circuit shown in FIG. 4, the power supply of the high-side drive circuit HDRV including the diode D9 and the capacitor C3 can generate only a positive voltage, and therefore normally ON that requires reverse bias (negative voltage for turning off). Type switch cannot be used for high side.

Further, since the power source of the high side drive circuit HDRV is generated by the diode D9 and the capacitor C3, the diode D9 has to be a high breakdown voltage diode and is expensive.

  An object of the present invention is to provide a drive circuit and a switching power supply device that can use a normally-on type switch for a high side.

In order to solve the above problems, a drive circuit of the present invention is a drive circuit that drives a high-side normally-on switch and a low-side normally-off switch that are connected in series to each other and connected in parallel to a DC power supply. A level shift circuit that converts a high-side control signal to a predetermined signal level; a high-side drive circuit that drives the normally-on type switch by a high-side control signal converted to a predetermined signal level by the level shift circuit; A low-side drive circuit that drives the normally-off switch by a low-side control signal;
A series circuit connected between a connection point of the normally-on type switch and the normally-off type switch and one end of the DC power supply, and a second capacitor and a first capacitor connected in series; The power supply voltage of the high-side drive circuit is supplied from two capacitors, and the power supply voltage of the low-side drive circuit is supplied from the first capacitor.

  The switching power supply device of the present invention includes a high-side normally-on type switch and a low-side normally-off type switch connected in series to each other and connected in parallel to a DC power source, A transformer primary winding and a resonance capacitor connected in parallel to the normally-off switch, a rectifying and smoothing circuit for rectifying and smoothing a voltage generated in the secondary winding of the transformer, and a high voltage based on the output voltage of the rectifying and smoothing circuit A control circuit for generating a side control signal and a low-side control signal; and a drive circuit for driving the normally-on type switch and the normally-off type switch based on the high-side control signal and the low-side control signal. , Any one of claims 1 to 3 Characterized in that it is a drive circuit according.

According to the present invention, at the time of starting the power supply to which DC power is supplied, the current flows through the normally-on type switch to the second capacitor and the first capacitor, so that the second capacitor is charged. Is supplied as a power supply voltage for the high-side drive circuit. For this reason, since a reverse bias can be supplied to the normally-on type switch, the normally-on type switch can be used.

1 is a configuration diagram of a switching power supply device having a drive circuit of Example 1. FIG. FIG. 6 is a diagram illustrating operation waveforms of respective units of the drive circuit according to the first embodiment. FIG. 3 is a diagram illustrating detailed operation waveforms of each part of the drive circuit according to the first embodiment. It is a block diagram which shows an example of the switching power supply device which has a conventional drive circuit.

  Hereinafter, a drive circuit and a switching power supply 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 switching power supply device having a drive circuit according to a first embodiment of the present invention. The drive circuit shown in FIG. 1 uses a resistor R1 (current limiting element) and a Zener diode ZD1 (voltage clamp element) instead of the starting resistor Ro and the diode D9 of the drive circuit shown in FIG. .

The switching power supply device shown in FIG. 1 uses a normally-on type switch for the high side. A normally-on switch is a switch that is turned on when the gate-source voltage is zero and turned off when the voltage is negative.

The normally-on type switch Q5 for the high side is replaced with a normally-off type switch Q2 made of a MOSFET of a Si device, and is made of a GaNFET of a normally-on type gallium nitride (GaN) device. The source of normally-on type switch Q5 is connected to one end of capacitor C3 (second capacitor), the cathode of Zener diode ZD1, the positive power supply terminal (+) of high side drive circuit HDRV, and one end of resistors R2 and R3. .

The other end of the capacitor C3 is connected to the anode of the Zener diode ZD1, one end of the resistor R1, the negative power supply terminal (−) of the high side drive circuit HDRV, and the anodes of the diodes D1 and D2. The other end of the resistor R1 is connected to the positive power supply terminal (+) of the low side drive circuit LDRV and one end of the capacitor C1 (first capacitor).

The capacitor C3 supplies the power supply voltage of the high side drive circuit HDRV, and the capacitor C1 supplies the power supply voltage of the low side drive circuit LDRV.

The Zener diode ZD1 clamps the voltage across the capacitor C3 to the breakdown voltage, and the power supply voltage to the high side drive circuit HDRV is determined by the breakdown voltage.

Since other configurations are the same as those of the conventional drive circuit and switching power supply device shown in FIG. 4, the same reference numerals are given to the same portions, and descriptions thereof are omitted.

The oscillator OSC and the voltage detection circuit 11 correspond to the control circuit of the present invention, and the diodes D7 and D8 and the capacitor C4 correspond to the rectifying and smoothing circuit of the present invention.

The pulse signal from the oscillator OSC corresponds to the low side control signal of the present invention, and the pulse signal obtained by inverting the pulse signal from the oscillator OSC corresponds to the high side control signal of the present invention.

Next, the operation of the drive circuit and the switching power supply device according to the first embodiment configured as described above will be described in detail with reference to operation waveforms shown in FIGS.

2, Vc1 to Vc3 are voltages across the capacitors C1 to C3, Iq3 and Iq4 are currents flowing through the drains of the FETs Q3 and Q4, VgsQ1 is a gate-source voltage of the normally-off switch Q1, and VgsQ5 is a normally-on switch Q5. A gate-source voltage, OSC, indicates a pulse signal from the oscillator OSC. In FIG. 3, IdQ1 is the drain current of the normally-off switch Q1, Ic2 is the current flowing through the capacitor C2, and VdsQ1 is the drain-source voltage of the normally-off switch Q1.

First, at the time of starting the power source to which the DC power source V1 is supplied (time t0 to t1), the normally-on type switch Q5 is in a conductive state, so V1 (positive electrode) → Q5 → C3 → R1 → C1 → V1 (negative electrode). The current flows through the path and the capacitors C3 and C1 are charged, so that the voltages Vc1 and Vc3 change as shown in FIG. In addition, since a current flows through a path of V1 (positive electrode) → Q5 → P1 → C2 → V1 (negative electrode) and the capacitor C2 is charged, the voltage Vc2 increases.

At this time, the voltage Vc3 of the capacitor C3 is a negative voltage with respect to the source potential of the normally-on switch Q5. By using the voltage Vc3 of the capacitor C3 as the power supply voltage of the high-side drive circuit HDRV, the high-side drive circuit HDRV is zero between the gate and source of the normally-on type switch Q5 with respect to the source potential of the normally-on type switch Q5. Since a voltage and a negative voltage can be output, the gate potential of the normally-on switch Q5 can be reverse-biased (negative voltage). That is, the normally-on type switch Q5 can be turned on / off.

Then, the voltage Vc1 of the capacitor C1 is supplied as the power supply voltage of the oscillator OSC and the low-side drive circuit LDRV, and the voltage Vc3 of the capacitor C3 is supplied as the power supply voltage of the high-side drive circuit HDRV. After time t1).

Then, the current Iq4 flows to the FET Q4 in synchronization with the falling edge of the pulse signal obtained by inverting the rising edge (time t2) of the pulse signal from the oscillator OSC, and the reset signal is input to the flip-flop circuit FF1. The mold switch Q5 is turned off. In addition, the normally-off type switch Q1 is turned on in synchronization with the rise of the pulse signal from the oscillator OSC (time t2).

Next, in synchronization with the rising edge of the pulse signal obtained by inverting the falling edge of the pulse signal from the oscillator OSC (time t3), the current Iq3 flows through the FET Q3, and the set signal is input to the flip-flop circuit FF1. The mullion switch Q5 is turned on. Further, the normally-off type switch Q1 is turned off in synchronization with the falling edge of the pulse signal from the oscillator OSC (time t3). Since the times t2 to t3 are the off period of the normally-on type switch Q5, the voltage Vc3 of the capacitor C3 is discharged from the original voltage.

Next, the current Iq4 flows through the FET Q4 in synchronization with the falling edge of the pulse signal obtained by inverting the rising edge (time t4) of the pulse signal from the oscillator OSC, and the reset signal is input to the flip-flop circuit FF1. The mullion switch Q5 is turned off. In addition, the normally-off switch Q1 is turned on in synchronization with the rise of the pulse signal from the oscillator OSC (time t4). Since the times t3 to t4 are the ON period of the normally-on type switch Q5, the voltage Vc3 of the capacitor C3 is charged to the original voltage.

In this way, the voltage Vc3 of the capacitor C3 is supplied to the high side drive circuit HDRV, and the normally-on type switch Q5 is turned on / off.

Next, the current resonance operation of the switching power supply device will be described with reference to FIG.

First, when the normally-off switch Q1 is turned on at times t10 to t12, a current Ic2 flows so that the resonance capacitor C2 is discharged. From time t10 to t12, the resonance current IdQ1 flows through the path C2-> P1-> Q1-> C2. The negative current at times t10 to t11 is a current flowing through the diode D6.

At this time, on the secondary side of the transformer T1, a current flows through a route of S2, D8, C4, and S2, and power is supplied to a load (not shown).

Next, when the normally-on type switch Q5 is turned on at times t13 to t15, a current Ic2 flows so that the capacitor C2 is charged. From time t13 to t15, the resonance current IdQ5 flows through a path of V1 (positive electrode) → Q5 → P1 → C2 → V1 (negative electrode). The negative current at times t13 to t14 is a current that flows through the diode D5.

At this time, on the secondary side of the transformer T1, a current flows through a path of S1, D7, C4, and S1, and power is supplied to a load (not shown).

As described above, according to the drive circuit of the first embodiment, when the power supply is activated, the normally-on type switch Q5 is turned on, the current flows in the order of the capacitor C3, the resistor R1, and the capacitor C1, and the capacitor C3 is charged. The voltage across the capacitor C3 is supplied as the power supply voltage for the high side drive circuit HDRV. For this reason, a normally-on type switch Q5 can be used.

Moreover, according to the switching power supply device of Example 1, switching loss can be reduced compared with MOSFET of Si device by using the normally-on type switch which consists of GaNFET for high side.

In FIG. 1, even if the connection of the primary winding P1 of the transformer T1 and the resonance capacitor C2 is changed between the drain-source of the normally-off switch Q1 to the drain-source of the normally-on switch Q5. good. Even in such a case, the same operation and effect as those of the switching power supply apparatus of the first embodiment can be obtained.

  The present invention is applicable to a power supply device.

V1 DC power supply T1 Transformer P1 Primary winding S1 First secondary winding S2 Second secondary winding Q1, Q2 Normally-off switch Q5 Normally-on switch Q3, Q4 FET
OSC Oscillator INV Inverter OST1, OST2 One-shot circuit D1-D9 Diode C1-C4 Capacitor FF1 Flip-flop circuit R0 Start-up resistor R1-R5 Resistor LDRV Low-side drive circuit HDRV High-side drive circuit 11 Voltage detection circuit ZD1 Zener diode LST Level shift circuit

Claims (4)

A drive circuit that drives a high-side normally-on type switch and a low-side normally-off type switch that are connected in series with each other and connected in parallel to a DC power source,
A level shift circuit that converts the high-side control signal into a predetermined signal level;
A high-side drive circuit that drives the normally-on type switch by a high-side control signal converted to a predetermined signal level by the level shift circuit;
A low-side drive circuit that drives the normally-off switch by a low-side control signal;
A series circuit in which a second capacitor and a first capacitor are connected in series, connected between a connection point of the normally-on type switch and the normally-off type switch and one end of the DC power supply;
The drive circuit, wherein the power supply voltage of the high-side drive circuit is supplied from the second capacitor, and the power supply voltage of the low-side drive circuit is supplied from the first capacitor.   2. The drive circuit according to claim 1, wherein a voltage clamp element is connected in parallel to the second capacitor in the series circuit.   3. The drive circuit according to claim 2, wherein a current limiting element is connected in series to the second capacitor and the first capacitor. A high-side normally-on switch and a low-side normally-off switch connected in series to each other and connected in parallel to the DC power supply;
A transformer primary winding and a resonance capacitor connected in series with each other and connected in parallel to the normally-on switch or the normally-off switch;
A rectifying and smoothing circuit for rectifying and smoothing a voltage generated in the secondary winding of the transformer;
A control circuit for generating a high-side control signal and a low-side control signal based on an output voltage of the rectifying and smoothing circuit;
A drive circuit that drives the normally-on switch and the normally-off switch based on the high-side control signal and the low-side control signal;
4. The switching power supply device according to claim 1, wherein the drive circuit is the drive circuit according to claim 1.

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