JPH0340517A - Driving/protecting circuit for power device - Google Patents

Abstract

PURPOSE:To eliminate the need for a reverse bias and to allow respective power source to be unitary by turning a gate emitter to low impedance at the time of turning off a power device in a driving circuit. CONSTITUTION:An input signal VIN from a microcomputer 1 is inputted to the driving circuit 2 and a turning-off circuit 11 through a pulse-by-pulse type latch circuit 10 and connected from the circuit 2 to the gate G of an IGBT 3 through gate resistor 4 as a power device. At the time of turning off the input signal, the gate G of the IGBT 3 is short-circuited to the ground (emitter potential of the IGBT 3) by the circuit 11 in the low impedance state. Consequently, the need for the reverse bias can be eliminated and the whole driving/ protecting circuit can be operated only by one power source.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a buff device circuit such as a power IC module that uses a voltage-controlled power device as an output element, and particularly to a buff device circuit such as a power IC module that uses a voltage-controlled power device as an output element. This invention relates to a drive/protection circuit for power devices with a short-circuit protection function.

[Conventional technology]

An example of a drive/overcurrent protection circuit for a voltage controlled power device conventionally used in a power device circuit will be described with reference to FIG. In Fig. 3, 1 is a microcomputer (hereinafter abbreviated as microcomputer), 2 is a drive (driver) circuit, and 3 is an IGBT as a voltage-controlled power device with built-in current detection.
is grounded, and the flefter C is connected to the inductive load 6. The input signal vrN from the microcomputer 1 is input to a drive circuit 2 for driving this IGBT 3, and is connected to the gate G of the IGBT 3 via a gate resistor 4. In order to apply a reverse bias to the gate G of the drive circuit 2, two power supplies, +VCC and -VXX, are supplied. In addition, the sense resistor 5 connected between the sense S and the emitter E of the IGBT 3 monitors the collector current IC of the 1GBT 3, and the voltage and the reference voltage source 70 reference voltage Vrefl are monitored.
By comparing the values with the comparator 8, overcurrent is detected, and when an overcurrent condition occurs, an abnormality signal Vv0 is output to the microcomputer 1.

Next, the operation will be explained with reference to the timing chart of the fourth TIA. In Fig. 4, the part marked with symbol I indicated by a thick arrow indicates the waveform during normal operation, the part marked with symbol ■ indicates the waveform during overcurrent, and the part marked with symbol ■ indicates the waveform during short circuit. There is.

In the normal state of the housing (the part marked with I), the gate applied voltage vGx, which is the output of the drive circuit 2, changes from -v■ in response to the input signal VIN shown in FIG. 4(d) from the microcomputer 1. The power level becomes +VCC (Fig. 4(b)).

Therefore, IGBT3 is in the on state and ib1 collector current Ia flows (Fig. 4 (withstanding). And collector current Ic
increases and exceeds the overcurrent detection level (part marked with symbol ■), when the collector current Ic exceeds the overcurrent detection level 21, an abnormal signal v is sent from the comparator 8 to the microcomputer 1.
yo is output (FIG. 4(C)). Then, the microcomputer 1 performs processing based on the abnormal signal and then changes the input signal VIN from the "H" level to the rLJ level (FIG. 4(d)). Therefore, the drive circuit 2 sets its output to the power level of -vn, reverse biases the gate G of the IGBT 3 to turn off the IGBT 3, and collects the collector current I
Block c. In addition, even in the state where a short circuit current flows during a short circuit indicated by the symbol sH (the part marked with a symbol ■), the current exceeds the overcurrent detection level 21, so the collector current Ic is cut off by the same operation as in the overcurrent state, and protection is achieved. can be done.

[Problem to be solved by the invention]

However, the drive and overcurrent protection circuits of conventional voltage-controlled power devices are configured as described above. Signal processing was required. Since the system uses microcomputer software, calculation time and sampling time for abnormal signals are required, so it takes time to apply feedback to the input signal. For this reason, if a short circuit occurs in the power device, the power device will be destroyed due to feedback 1, making it necessary to use a device with high short-circuit tolerance.・Characteristics such as switching speed p Wax (mat) will be adversely affected. It was used in the same condition. Furthermore, when a power device is connected in a bridge configuration, it is necessary to reverse bias the gate when the device is off in order to prevent dma/dt from being applied to the off-state device, causing the gate voltage to rise and malfunctioning. For this reason, it was necessary to use a drive circuit with two power supplies, or to use a reverse bias diode circuit or a regulator circuit with one power supply.

The present invention was made in order to solve the above problems, and it is possible to use devices with good characteristics such as switching speed and VCI (sat), regardless of the short circuit tolerance of power devices such as IGET. It is an object of the present invention to obtain an overcurrent protection/short circuit protection circuit, and also to obtain a drive circuit which uses a single power supply and does not cause malfunction of gate voltage due to dma/dt due to dangerous reverse bias.

[Means to solve the problem]

The driving/overcurrent/short-circuit protection circuit for a voltage-controlled power device according to the present invention performs an operation for each input pulse to reduce the voltage applied to the gate of the back-device and the collector current at the same time that a short circuit occurs. At the same time, overcurrent protection takes into account the recovery current of the freewheeling diode in any case from overcurrent occurrence to inductive loads, and directly shuts off the drive circuit after a certain delay time.

When the drive circuit is turned off, the gate and emitter of a power device such as an IGBT are short-circuited with low impedance.

[Effect]

The short-circuit protection circuit according to the present invention can reduce the gate applied voltage and reduce the collector current at the same time a short circuit occurs, so it is possible to set a detection value for determining a short circuit according to the short-circuit tolerance of a power device such as an IGBT. , the device with the best switching time rV(J(sat)) can be used freely.In addition, the overcurrent protection circuit can be used simply by providing a delay time to remove the freewheel coverage current. This enables high-speed operation.In addition, there is no need for signal processing by the microcomputer, and the microcomputer only needs to detect the status based on the abnormal signal, reducing the load on one microcomputer.Also, when a back-up device such as an IGBT is turned off, By creating a low impedance shot between the gate and emitter, gate malfunctions due to d/at can be prevented, and a reverse bias circuit is not required, making it possible to operate all drive protection circuits with a single power supply. becomes.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of a power device drive/protection circuit according to the present invention.

In FIG. 1, an input signal vI)1 from a microcomputer 1 is input to a drive circuit 2ε turn-off circuit 11 via a pulse 0-by-pulse type latch circuit 10, and is also input from the drive circuit 2 to a gate resistor 4. Gate G of IGBT3 via
connected to. When the input signal is off, the turn-off circuit 11 connects the gate G of the IGBT 3 to the ground (emitter potential of the IGBT 3) with low impedance. In addition, the collector current Ic of the 11GBT3 is monitored by the sense resistor 5 connected between the sense Sε emitter E of the IGBT3, and the short circuit detection is based on the reference voltage vran of the reference voltage source 12.The overcurrent detection is based on the reference voltage source T. Voltage V. fl (<Vraf
comparator 13.z) and voltage comparison respectively. This is done using comparator 8. Further, the output of the comparator 13 for short circuit protection is input to a pulse-by-pulse type latch circuit 14 to which the input signal vIN is input, and when a short circuit occurs, the output of the drive circuit 2 is output while the input signal is on. The voltage is resistance-divided by the gate resistors 4 and 4 and is connected to be applied to the gate of the TGBT 3. The output of the overcurrent protection comparator 8 is passed through a delay circuit 9 with a predetermined delay time td to remove the recovery current due to a freewheeling diode (not shown) on the inductive load 6 side. , a pulse-by-pulse type switch circuit 1 to output an abnormal signal to the microcomputer 1 and cut off the output of the drive circuit 2.
It is entered as 0. &Th, the same reference numerals in the figures indicate the same or Japanese parts.

Next, the operation of the configuration of the above embodiment will be explained with reference to the timing chart of FIG. 1. In normal operation (portion I), in response to the input signal vIN from the microcomputer 1 shown in FIG. (Fig. 2(b)), IGBT3 is turned on and the collector current Ic
flows (Fig. 2 (&)).

Then, collector current Ic increases and overcurrent detection level 2
When the value exceeds 1 (the part marked with symbol ■), the output signal of the comparator 8 constituting the overcurrent protection circuit is delayed by the delay time td of the delay circuit 9, passes through the latch circuit 10, and shuts off the drive circuit 2. The gate applied voltage VGI of the output is set to “0”.
"■, and at the same time outputs an abnormality signal VFO to the microcomputer 1. Therefore, the microcomputer 1 only needs to detect the occurrence of an abnormal signal, and when the input signal reaches the rLJ level, the pulse-by-pulse type latch circuit 10 automatically resets the latch in the abnormal state.

In addition, if a short circuit current flows during a short circuit indicated by the symbol SH (
The part marked with symbol ■) indicates that at the same time the collector current Ic exceeds the short-circuit detection level 22, the output of the comparator 13 constituting the short-circuit protection circuit reaches the pulse-by-pulse type latch circuit 1.
4 is input. As a result, one gate applied voltage VCC is lowered from the VCC power supply level by the resistance division of the gate resistors 4 and 4a (FIG. 2(b)), and the input signal is latched by the latch circuit 14 while the input signal is at the rHJ level. Then, the short-circuit protection circuit operates and the collector current IC decreases, but if the current value at this time is equal to or higher than the overcurrent detection level 21, the gate of IGBT3 is cut off after the rtctJ time delay as in the overcurrent state. and outputs an abnormal signal (Fig. 2(C)).

Furthermore, the timing of the drive circuit 2 and the turn-off circuit 11 is such that just before the output of the drive circuit 2 changes from the rLJ level to the rL (J level), the turn-off circuit 11 sets a high impedance between the gate and emitter of the IGBT 3 to "H". Immediately after going from the level to the rLJ level, the impedance between the gate and emitter is made low.As a result, the IGB
When T3 is off, the turn-off circuit 11 causes 9IG
The gate and emitter of BT3 are shorted to low impedance. Therefore, it is possible to prevent malfunctions due to gate voltage fluctuations caused by dma/dt that occur when the IGBT is configured in a bridge configuration.

In the above embodiment, an IGBT with built-in current detection was described as a power device, but any voltage-controlled power device may be used, such as a MOSFET.Also, even if it is not a device with built-in current detection, other By using a sensor that monitors the collector current and converts the power into voltage, the same effects as in the above embodiment can be achieved.

In addition, when the short-circuit protection circuit operates, the above embodiment describes the case where the collector current is above the overcurrent detection level, but when the collector current is below the overcurrent detection level, the short-circuit protection circuit output ( If the output of the pulse-by-pulse latch circuit 14) is fed back to the overcurrent detection reference voltage source 7 and the overcurrent detection level is lowered when a short circuit occurs, the same effect as in the above embodiment can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, by making the gate and emitter of the drive circuit low impedance when the power device is in the off state, reverse bias is not required.
In addition to realizing a power supply, the combination of a short-circuit protection circuit and an overcurrent protection circuit allows use without considering the short-circuit tolerance of a single power device. Furthermore, since protection is performed without requiring external feedback from a microcomputer, high-speed operation is possible, and an inexpensive circuit can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block configuration diagram of a power device drive/protection circuit according to an embodiment of the present invention, Fig. 2 is a timing chart for explaining the operation of the embodiment, and Fig. 3 is a drive/overcurrent protection circuit according to a conventional example. The block diagram of the circuit and FIG. 4 is its timing chart. 2.O.◆Drive circuit, 3...IGBT, 4. 4 & --- Gate resistance, 5 --- Sense resistor, 6
...Inductive load, T, 12...Reference voltage source, 8
... Comparator for overcurrent protection, 9--Delay circuit, 10, 14... Latch circuit, 11... Turn-off circuit, 13-- Comparator for short-circuit protection.

Claims (1)

[Claims] In a drive circuit for a voltage-controlled power device, a turn-off circuit provides low impedance between the gate and emitter of the power device when the power device is off, and a signal from a current sensor of the power device is compared with a first reference voltage. , an overcurrent protection circuit whose output is fed back to the drive circuit through a delay circuit, and a signal from the current sensor is compared with a second reference voltage, and the output of the current sensor is used to reduce the output of the drive circuit, and the power device is activated. A drive/protection circuit for a power device, characterized in that it is equipped with a short-circuit protection circuit that applies voltage to the gate of the power device.