Analysis of IGBT drive circuit M57962L
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IGBT is a composite full-controlled voltage-driven power electronic device.
Introduction to the drive circuit M57962L.
How the M57962L works.
solution:
A threshold voltage of 2.5V to 5.0V makes the IGBT sensitive to gate charge accumulation.
The magnitude of the sense tube voltage drop VCE identifies whether the IGBT is overcurrent.
The closed soft-shutdown function improves IGBT safety.
IGBT is a new type of power device, namely insulated gate Bipolar Transistor, which is a composite full-control voltage-driven power electronic device that appeared at the end of the last century. It combines the advantages of GTR and MOSFET: high input impedance, high switching frequency, large operating current, etc., and is widely used in inverters, switching power supplies, arc welding power supplies and other fields.
The IGBT has a threshold voltage of 2.5V to 5.0V and has a capacitive input impedance, so the IGBT is sensitive to gate charge accumulation. Therefore, the drive circuit must be reliable, to ensure that there is a discharge circuit with low impedance value, and the internal resistance of the drive power supply must be small, that is, the charge and discharge speed of the gate capacitor should be fast to ensure that the VGE has steep front and rear edges, so that the IGBT Switching losses should be as small as possible.
When the IGBT is subjected to a short-circuit current, the IGBT can be effectively protected if it can be turned off in time. One way to identify whether an IGBT is overcurrent is to measure the magnitude of its tube voltage drop, VCE. When the IGBT is turned on, if VCE is too high, a short circuit occurs, and the IGBT needs to be turned off immediately. When the IGBT is turned off by overcurrent, due to the large current amplitude in the IGBT, if the IGBT is turned off quickly, Ldi/dt will be too high, and a high peak voltage will be generated at both ends of the IGBT, which will easily damage the IGBT. "Soft slow turn off" method. The M57962L drive circuit is designed according to the above theory.
Introduction to the drive circuit M57962L
The M57962L is a Hybrid Integrated Circuit For Driving IGBT Modules designed by Mitsubishi Electric Corporation to drive IGBTs. The drive module is equipped with a 2500V high isolation voltage optocoupler, overcurrent protection circuit and overcurrent protection output terminal, with closed short circuit protection. The M57962L is a high-speed drive circuit with a drive signal delay of tPLH and tPHL of up to 1.50μs. It can drive IGBT modules of 600V/400V class.
M57962L working program: When the power is turned on, first self-test to detect whether the IGBT is overloaded or shorted. If overload or short circuit occurs, the collector potential of the IGBT rises, the current flowing into the detection circuit through the external diode increases, the gate turn-off circuit operates, the gate drive signal of the IGBT is cut off, and the low level "overload" is output at the "8" pin. / Short circuit indication signal. When the GBT is normal, the input signal is passed through the optocoupler interface circuit, and then the IGBT is driven by the driver stage power amplification.
How does the M57962L work?
The M57962L uses dual power supplies + Vcc and VEE. The principle is shown in Figure 1. The circuit consists of: (1) amplified isolation circuit; (2) timing reset circuit; (3) overcurrent detection circuit; (4) overcurrent output circuit.
Figure 1 M57962L chip schematic
a Normal opening process
When the control circuit makes the M57962L input terminals 13 and 14 have 10mA current, the optocoupler IC1 is turned on, the potential at point A drops rapidly to VEE, and the output of pin 2 of IC2A is high level Vcc, then the transistors V2 and V4 are turned on, V3 V5 is turned off, V7 is turned on, Vcc is applied to R17, and R18/(R17+ R18) is greater than R16/(R15+ R16), causing pin 13 of IC2D to be low, V6 is off, R4/(R3 +R4) Greater than R16 (R15 + R16) makes IC2B's 13 pin cut off, so IC2's 14 pin is high level V1, cut off, M57962L's 8 pin does not output fault signal.
When there is no current at the input terminals 13 and 14 of the M57962L, IC1 is turned off, and the potential at point A rises to make the pin 2 of IC2A low, so that V3 and V5 are turned on, and V2 and V4 are turned off. The gate of the gigabyte (GATE) is turned on to VEE through V5, and the IGBT is turned off. The 14-pin output of IC2C is low, which makes V1 and V7 turn on, keeping IC2B and IC2D unchanged.
b short circuit fault status
If the IGBT has been turned on, the voltage at E and F rises. After the protection delay, V7 is turned off, and the 13 pin of IC2D becomes off, making V6 turn on. At the 8th leg of the M57962L, the fault signal is output. At the same time, V6 makes the A point low and VEE enters the closed soft-off process. At this time, there are no signals on the 13th and 14th legs of the M57962L, which has no effect on the state of the M57962L. C6 discharges through R14 and R21 to slowly decrease the potential at point G, thereby achieving soft shutdown. At the same time, C1 discharges the potential of pin 7 of IC2B slowly by R4 discharge. When C1 discharge ends, the soft shutdown process will be interrupted. If the short-circuit fault of the IGBT disappears, the circuit can resume normal operation; if the fault of the IGBT disappears, the M57962L outputs a pulse signal with a period of 1.3ms (the front edge is steep and the trailing edge is slow).
The M57962L is powered by a +15V, -10V dual supply. Due to the -10V shutdown voltage, it can be turned off more reliably, and has a closed soft-shutdown function, which makes the IGBT work safer.
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