JP2002223157A - Drive circuit for voltage drive transistor such as mosfet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit for a voltage drive transistor(TR) such as a MOSFET that allows simple control, reduces the number of components and can be downsized at a low cost. SOLUTION: A gate of a MOSFET 1 is connected to a positive terminal of a power supply 2 for a drive circuit via a 1st switching element SW1. A 1st diode D1 is connected to block flowing of a current to the gate from the power supply 2 for the drive circuit is connected between the positive terminal of the power supply 2 for the drive circuit and the gate of the MOSFET 1. A 2nd diode D2 whose cathode is connected to a resonance coil L1 is connected to a connecting point between the 1st switching element SW1 and the resonance coil L1. One terminal of a 2nd switching element SW2 is connected to an anode of the 2nd diode D2 and the other terminal of the 2nd switching element SW2 is grounded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a MOSFET (MO).
The present invention relates to a driving circuit for a voltage-driven transistor such as an S field-effect transistor) or an IGBT (an insulated gate bipolar transistor combining a MOSFET and a bipolar transistor).

[0002]

2. Description of the Related Art Conventionally, a semiconductor switch capable of high-speed on / off control has been used for controlling power supply to a load. In particular, a field-effect transistor (FET) has been used as a high-speed switching element. And MOSFET
(Metal Oxide Semiconductor Field Effect Transistor)
Using a resonance coil that resonates with the gate-source capacitance (hereinafter, simply referred to as gate capacitance) of the above, the power consumption is small and as a drive circuit that can drive the MOSFET with a single power supply,
The circuit shown in FIG. 5 is disclosed in JP-A-5-252014.

In this drive circuit, when the three switching elements SW1 to SW3 are turned off, first, when the first switching element SW1 is turned on, the drive circuit power supply 31 is turned on.
, A voltage is applied to the gate of the MOSFET 32, and when the gate voltage exceeds a predetermined voltage, the MOSFET 32 is turned on. In addition, due to the resonance between the gate capacitance Ciss and the resonance coil 33, charging is performed until the gate voltage becomes approximately twice the voltage of the drive circuit power supply 31. Next, when the first switching element SW1 is turned off and then the third switching element SW3 is turned on, the resonance between the gate capacitance Ciss and the resonance coil 34 causes the resonance coil 34 and the third switching element SW3 to pass from the gate. A current flows to the source via the.

[0004] Simply, the first and third switching elements S
If only W1 and SW3 are switched alternately, the gate voltage will increase each time switching is performed. Therefore, the gate voltage detection unit 35 is provided, and the first and second switching elements SW1 and SW2 are selectively used depending on the gate voltage, thereby preventing the gate voltage from continuing to increase. That is, as shown in FIG. 6, after the on / off control of the first and third switching elements SW1, SW3, the on / off control of the second switching element SW2 and the third switching element SW3 is performed. Then, when the positive peak of the gate voltage becomes smaller than the set value (E / 2), the first switching element SW1 is turned on / off instead of the second switching element SW2.

[0005]

In the above driving circuit,
A gate voltage detector 35 is provided to detect the gate voltage of the MOSFET 32, and based on the value, select one of the first and second switching elements SW1 and SW2, and alternately select the first and second switching elements SW1 and SW3. Performs on / off control. Therefore, the gate voltage detection unit 35 becomes indispensable, and the driving circuit becomes large and the manufacturing cost increases. There is also a problem that control becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the purpose of simplifying control, reducing the number of parts, and enabling miniaturization and cost reduction.
An object of the present invention is to provide a driving circuit for a voltage-driven transistor such as an OSFET.

[0007]

According to the first aspect of the present invention, there is provided a driving circuit for a voltage-driven transistor such as a MOSFET driven based on a voltage applied to a gate. A first switching element connected to the power supply for the driving circuit, a resonance inductor connected between the first switching element and the gate of the voltage-driven transistor, and a gate of the voltage-driven transistor. A first diode connected between the power supply for the drive circuit, and a first diode connected to prevent a current from flowing from the power supply for the drive circuit to the gate; a second switching element and a second diode; Are connected in series, one end is connected to the resonance inductor on the first switching element side, and the other end is grounded. Said second diode second
And a circuit connected so as to prevent a current from flowing from the switching element to the gate side.

In the present invention, when the first switching element is first turned on from the state where the first and second switching elements are off, the first switching element and the resonance inductor are connected to the gate of the voltage-driven transistor. A current flows to turn on the voltage-driven transistor. Due to the resonance phenomenon between the resonance inductor and the gate capacitance, the resonance inductor keeps flowing current even when the gate voltage becomes higher than the voltage of the drive circuit power supply. Then, the gate voltage continues to increase to twice the voltage of the power supply for the drive circuit, but when the gate voltage becomes the sum of the voltage of the power supply for the drive circuit and the ON voltage of the first diode, the first The diode is turned on, and the current of the resonance inductor flows through the first diode. As a result, the gate voltage is substantially maintained at the voltage of the power supply for the drive circuit. After the current flowing through the resonance inductor becomes zero, the first switching element is turned off.

Next, when the second switching element is turned on, a current flows from the gate via the resonance inductor and the second diode, and when the gate voltage falls below a predetermined voltage, the voltage-driven transistor is turned off. Due to the resonance phenomenon between the resonance inductor and the gate capacitance, the current continues to flow even when the gate voltage becomes zero or less, and the current of the resonance inductor becomes zero when the gate voltage becomes −E. Next, the current of the resonance inductor tries to reverse, but is blocked by the second diode, no current flows, and the gate voltage is held at -E. When the current of the resonance inductor becomes zero, the second switching element is turned off. Hereinafter, similarly, the first switching element and the second switching element are alternately turned on and off.

Since the time when the current flowing through the resonance inductor becomes zero can be set at the stage of designing the circuit, the current is detected at the time of control to turn on / off the first and second switching elements.
There is no need to provide a detector to determine the off-time,
To that extent, the number of parts is reduced, and downsizing and cost reduction can be achieved. In addition, the ON / OFF of two switching elements
Because of the off control, the control becomes simpler.

According to a second aspect of the present invention, in the first aspect, the second switching element and the second switching element are connected to each other.
A circuit in which a third switching element and a third diode are connected in series is connected in parallel to a circuit in which the third diode is connected in series, and the third diode is connected to the third diode from the resonance inductor side. 3 are connected so as to block the flow of current to the switching element side.

According to the present invention, when the first switching element is first turned on from the state where the first to third switching elements are off, the voltage-driven transistor is turned on in the same manner as described above, and the gate voltage is reduced. After the voltage almost rises to the voltage of the power supply for the drive circuit, the voltage is maintained at that voltage. The first switching element is turned off while the third switching element is turned on. When the first switching element is turned off, the current of the resonance inductor becomes a state in which a circuit including the third switching element, the third diode, the resonance inductor, the first diode, and the power supply for the driving circuit is closed, The energy of the resonance inductor is returned to the drive circuit power supply as a current. Therefore, the ON time of the voltage-driven transistor can be made shorter than that of the first aspect. In addition, since the energy of the resonance inductor is returned to the power supply for the drive circuit, energy loss is reduced.

Next, after the current flowing through the resonance inductor becomes zero, the second switching element is turned on, and the second switching element is turned on.
The third switching element is turned off after the switching element is turned on. When the second switching element is turned on, the voltage-driven transistor is turned off in the same manner as described above, and the gate voltage is held at -E. When the current of the resonance inductor becomes zero, the second switching element is turned off. Hereinafter, similarly, the first to third switching elements are ON / OFF controlled in the same order. Although the number of switching elements is three, which is the same as that of the prior art, a gate voltage detection unit is not required, and control of the switching elements is simplified.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment in which the present invention is embodied in a MOSFET drive circuit as a voltage-driven transistor will be described below with reference to FIGS.

As shown in FIG. 1, an n-channel MOSF
ET1 is grounded at its source, and its gate is connected to the positive terminal of the drive circuit power supply 2 via a resonance coil L1 as a resonance inductor and a first switching element SW1. Plus terminal of power supply 2 for drive circuit and MOSFE
A first diode D1 is connected between the gate of T1 and the first diode D1 so as to prevent a current from flowing from the drive circuit power supply 2 to the gate. That is, the first diode D1 has a cathode connected to the drive circuit power supply 2 and an anode connected to the gate.

A connection point between the first switching element SW1 and the resonance coil L1 is connected to a second diode D2 with the cathode side connected to the resonance coil L1. One end of a second switching element SW2 is connected to the anode of the second diode D2, and the other end of the second switching element SW2 is grounded. That is, one end is connected to the resonance coil L1 such that a circuit in which the second switching element SW2 and the second diode D2 are connected in series prevents a current from flowing from the second switching element SW2 to the gate side. On the other hand, the first switching element SW1
It is connected at the side and provided with the other end grounded.

The first and second switching elements SW1, SW1
SW2 is controlled to be turned on and off by a control signal from a control device (not shown). Next, the operation of the driving circuit configured as described above will be described. The drive circuit is used in a state where the drain of the MOSFET 1 is connected to a load driving power supply via a load (not shown).

The switching elements SW1 and SW2 are on / off controlled based on a control signal from a control device. MO
When the first switching element SW1 is first turned on from the state where the SFET1 and both the switching elements SW1 and SW2 are off, a current IL flows through the path of the first switching element SW1 → the resonance coil L1 → the gate of the MOSFET1. Then, electric charge is accumulated in the gate capacitance of the MOSFET 1 by the current IL (the gate capacitance is charged), and when the gate voltage Vgs exceeds a predetermined value, the MOSFET 1 is turned on.

Due to the resonance phenomenon between the resonance coil L1 and the gate capacitance, even if the gate voltage Vgs becomes higher than the voltage E of the power supply 2 for the drive circuit, the resonance coil L1 tries to keep the current flowing, and the gate voltage Vgs becomes the drive voltage for the drive circuit. Double voltage 2 of power supply 2
Try to keep rising to E. However, since the first diode D1 exists, when the gate voltage Vgs becomes the sum of the voltage E of the drive circuit power supply 2 and the ON voltage of the first diode D1, the first diode D1 turns on, The current of the resonance coil L1 flows through the first diode D1.
As a result, the gate voltage Vgs is substantially held (clamped) at the voltage E of the drive circuit power supply 2. The resonance coil L1 is the first
Gradually loses energy due to the on-voltage of the diode D1, and the current IL decreases. And the resonance coil L
After the current IL flowing through 1 becomes zero, the first switching element SW1 is turned off. It should be noted that the time from when the first diode D1 is turned on until the current IL becomes zero is set to a predetermined value determined by measurement using a model in the design stage of the drive circuit.

Next, when the second switching element SW2 is turned on, a current flows from the gate through the path of the resonance coil L1, the second diode D2, and the second switching element SW2, and the gate voltage Vgs falls below a predetermined voltage. MOSF
ET1 turns off. Due to the resonance phenomenon between the resonance coil L1 and the gate capacitance, the current continues to flow even when the gate voltage Vgs becomes zero or less, and the current of the resonance coil L1 becomes zero when the gate voltage Vgs becomes -E. Next, the resonance coil L1
, The current is blocked by the second diode D2 and no current flows, and the gate voltage Vgs is maintained at -E. When the current of the resonance coil L1 becomes zero, the second switching element SW2 is turned off.

Next, when the first switching element SW1 is turned on, a current IL flows again through the path of the first switching element SW1, the resonance coil L1, and the gate of the MOSFET 1, and the MOSFET 1 is turned on in the same manner as described above. Then, due to the resonance phenomenon between the resonance coil L1 and the gate capacitance,
Even when the gate voltage Vgs becomes higher than the voltage E of the power supply 2 for the drive circuit, the resonance coil L1 tries to keep the current flowing. Since the gate voltage at the time when the first switching element SW1 is turned on is −E, the maximum value of the current IL flowing through the resonance coil L1 becomes the first value when the gate voltage is zero.
Becomes larger than when the switching element SW1 is turned on. Further, the gate voltage Vgs tends to keep rising to 3E. However, when the gate voltage Vgs becomes the sum of the voltage E of the drive circuit power supply 2 and the on-voltage of the first diode D1, the first diode D1 turns on, and the gate voltage Vgs becomes substantially equal to E. Is clamped to.

In the same manner, the second switching element SW2 and the first switching element SW1 are alternately turned on and off in the same manner, and the MOSFET 1 is turned on and off. The current IL and the gate voltage Vgs associated with turning on and off the switching elements SW1 and SW2 change as shown in FIG.

This embodiment has the following effects. (1) The first switching element SW1 and the resonance inductor (resonance coil L1) are connected between the drive circuit power supply 2 and the gate of the MOSFET 1 (voltage-driven transistor), and the gate of the MOSFET 1 and the drive are connected. A first diode D is connected between the first power supply circuit 2 and the circuit power supply 2 to prevent a current from flowing from the drive circuit power supply 2 to the gate.
1 is connected. Therefore, when the first switching element SW1 is turned on, the resonance coil L1 and the MOSFE
It is possible to avoid the current from continuing to flow so that the gate voltage becomes higher than the voltage of the drive circuit power supply 2 due to the resonance phenomenon with the gate capacitance of T1. Can be held. As a result, unlike the conventional device, the first and second switching elements SW
The gate voltage does not continue to rise even if control for alternately turning on and off the SW1 and SW2 is repeated, so that a voltage detection unit for detecting the gate voltage is not required, which simplifies the structure of the drive circuit and reduces the size of the drive circuit. , And reduction of manufacturing cost.

(2) In the state where the first switching element SW1 is turned on, the time until the current IL flowing through the resonance coil L1 becomes zero is measured in advance by a model driving circuit, thereby designing the driving circuit. Can be set to a predetermined value. Therefore, the on / off control of the first switching element SW1 can be appropriately performed without detecting the current IL, and the control is simplified.

(3) A circuit in which the second switching element SW2 and the second diode D2 are connected in series has one end connected to the resonance coil L1 by the first switching element SW2.
Connected at one side and grounded at the other end,
Diode D2 blocks the flow of current from the second switching element SW2 to the gate side. Therefore, MO
Second switching element S for turning off SFET1
When W2 is turned off, the charge stored in the gate is
When the MOSFET 1 is turned off because it is pulled out by the resonance phenomenon between the gate capacitance of the ET1 and the resonance coil L1,
The voltage change near the off threshold of MOSFET 1 becomes faster,
Switching time from on to off is shortened, and switching loss can be reduced.

(4) Since an n-channel MOSFET is used as the MOSFET 1, a transistor for a large current can be easily obtained. (5) Since the resonance coil L1 is connected as the resonance inductor, a circuit that satisfies the resonance conditions is provided, compared to a configuration in which resonance is caused by using the inductance of the wiring without providing the resonance coil L1. It is easier to form.

(6) Both switching elements SW1, SW
No. 2 is turned on and turned off in the state where the current is zero, and the current becomes zero current switching, and the switching loss is reduced.

(Second Embodiment) Next, a second embodiment will be described with reference to FIGS. In this embodiment, a configuration for turning off the MOSFET 1 is different from that of the above embodiment. The same parts as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 3, a third switching element SW3 and a third diode D3 are connected in series to a circuit in which a second switching element SW2 and a second diode D2 are connected in series. Circuits are connected in parallel. The third diode D3 is connected so as to prevent a current from flowing from the resonance coil L1 to the third switching element SW3. In this embodiment, the third diode D3 has an anode connected to the cathode of the second diode D2 and a cathode connected to the third switching element SW3.
Is connected to one end. Third switching element SW
The other end of 3 is grounded. Each switching element SW1
SW3 are controlled to be turned on / off based on a control signal from a control device (not shown).

In this drive circuit, when the first switching element SW1 is first turned on from the state where the first to third switching elements SW1 to SW3 are off, the MOSFET 1 is turned on in the same manner as in the above embodiment. At the same time, the gate voltage substantially rises to the voltage E of the drive circuit power supply 2 and is maintained at that voltage. Next, after the third switching element SW3 is turned on and the current IL starts flowing through the first diode D1, the first switching element SW1 is turned off. First switching element SW
When 1 is turned off, the circuit including the third switching element SW3, the third diode D3, the resonance coil L1, the first diode D1, and the power supply 2 for the driving circuit is closed. Then, the current of the resonance coil L1 flows through the path of the third switching element SW3 → the third diode D3 → the resonance coil L1 → the first diode D1 → the power supply 2 for the drive circuit, and the energy of the resonance coil L1 is used for the drive circuit. Returned to power supply 2.

Next, after the current flowing through the resonance coil L1 becomes zero, the second switching element SW2 is turned on,
The third switching element SW3 is turned off after the second switching element SW2 is turned on. When the second switching element SW2 is turned on, the MOSF
ET1 is turned off and the gate voltage is kept at -E.
When the current of the resonance coil L1 becomes zero, the second switching element SW2 is turned off. Hereinafter, similarly, the first to third switching elements SW1 to SW3 are on / off controlled in the same order.

This embodiment has the following effects in addition to the same effects as (1) to (6) of the first embodiment. (7) Since the energy of the resonance inductor (resonance coil L1) is returned to the drive circuit power supply 2, energy loss is reduced.

(8) Compared to the first embodiment in which the current IL becomes zero due to the loss of energy of the resonance coil L1 due to the ON voltage of the first diode D1, the current IL becomes zero. Time to M
The ON time of the OSFET 1 can be shortened.

(9) Although the number of switching elements is three, which is the same as that of the prior art, the control of the switching elements is simplified because the gate voltage detecting unit is not required. The embodiment is not limited to the above, and may be configured as follows, for example.

The second switching element SW2 and the second switching element SW2
The order of connection in the circuit in which the diode D2 is connected in series is not limited to the order of the above embodiment, and the anode of the second diode D2 is grounded and the second switching element SW2 is connected to the cathode. May be adopted. In this case, the same operation and effect as those of the above-described embodiment in which the connection order is reversed can be obtained.

The third switching element SW3 and the third switching element
The connection order of the two in the circuit in which the diode D3 is connected in series is not limited to the order of the above embodiment, and the cathode of the third diode D3 is grounded, and the third switching element SW3 is connected to the anode. May be adopted. In this case, the same operation and effect as those of the above-described embodiment in which the connection order is reversed can be obtained.

The resonance coil L is used as the resonance inductor.
Instead of providing 1, the inductance of the wiring may be used. ○ Instead of a MOSFET as a voltage-driven transistor, an insulated gate bipolar transistor (IGB) combining a MOSFET and a bipolar transistor
The present invention may be applied to a driving circuit using T).

A plurality of MOSFETs 1 to be driven may be provided, and a gate of each MOSFET 1 may be connected to a connection point between the resonance coil L1 and the first diode D1. In this case, a plurality of MOSFETs 1 can be driven without increasing the number of switching elements SW1 and SW2. It is preferable to provide a resistor connected in series for each gate of each MOSFET 1 according to driving conditions such as high-frequency operation.

The invention (technical idea) grasped from the above embodiment will be described below. (1) The invention according to claim 1, wherein the first switching element and the second switching element are provided with a control section for alternately outputting an on / off control signal at a predetermined timing. Driver circuit for transistors.

(2) In the invention according to claim 2,
A MOSF provided with a control unit that outputs an on / off control signal at a predetermined timing in the order of the first switching element, the third switching element, and the second switching element
Drive circuit for voltage-driven transistors such as ET.

(3) In the invention described in any one of the first, second, first and second aspects, a resonance coil is connected as the resonance inductor. (4) In the invention according to any one of claims 1, 2, (1) and (2), an inductance of a wiring is used as the resonance inductor.

(5) Claims 1, 2 and (1) to
In the invention according to any one of (4) and (4), a MOSFET is used as the voltage-driven transistor.

[0043]

As described in detail above, according to the first and second aspects of the present invention, the control is simplified, and
Since the number of parts is reduced, miniaturization and cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a drive circuit according to a first embodiment.

FIG. 2 is a waveform chart showing changes in voltage and current due to switching.

FIG. 3 is a circuit diagram of a drive circuit according to a second embodiment.

FIG. 4 is a waveform chart showing changes in voltage and current according to the second embodiment.

FIG. 5 is a circuit diagram showing a conventional driving circuit.

FIG. 6 is a waveform diagram showing changes in voltage and current in a conventional example.

[Explanation of symbols]

1 .... MOSFET as voltage-driven transistor, 2.
... Power supply for driving circuit, D1 first diode, D2 second diode, D3 third diode, L1 resonance coil as resonance inductor, SW1 first switching element, SW2 second Switching element, SW
3. Third switching element.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiki Sakata 2-1-1 Toyota-cho, Kariya-shi, Aichi F-term in Toyota Industries Corporation (reference) 5H740 BA12 BB07 BB08 HH07 JA21 KK01 5J055 AX44 AX51 AX62 BX16 CX13 DX22 DX65 EX07 EX12 EX21 EY00 EY05 EY12 EY21 FX12 FX17 FX35 GX01 GX04

Claims (2)

[Claims] 1. A drive circuit for a voltage-driven transistor such as a MOSFET driven based on a voltage applied to a gate, comprising: a first switching element connected to a power supply for a drive circuit; A resonance inductor connected between a switching element and the gate of the voltage-driven transistor; a resonance inductor connected between the gate of the voltage-driven transistor and the power supply for the drive circuit; and A first connected to block current flow to the gate
A second switching element and a second diode are connected in series, and one end is connected to the resonance inductor on the first switching element side, and the other end is grounded, and A circuit connected to the second diode to block a current flow from the second switching element to the gate side.
Drive circuit for voltage-driven transistors such as FETs. 2. A circuit in which a third switching element and a third diode are connected in series is connected in parallel to a circuit in which the second switching element and a second diode are connected in series, 2. The drive circuit for a voltage-driven transistor such as a MOSFET according to claim 1, wherein the third diode is connected so as to prevent a current from flowing from the resonance inductor to the third switching element.