The basic difference is that the resistance offered by the main conducting channel when current flows through the device in its ON state is very much smaller in the IGBT. The second function of this passive resistor network. The resistor diode network in the gate drive circuit, (consisting of D1, R1, and R2) serves the same purpose as described in Fig. This means that it should be useable to upto around 1kHz (rise/fall time << 1/10th of waveform period), Practically this is safe to use upto around 2kHz or so at around 4A and 6V drive voltage available, provided you've a reasonable heatsink on the MOS (For IRFZ44N). The principal of operation and Gate drive circuits for the insulated gate bipolar transistor are very similar to that of the N-channel power MOSFET. The parallel resistor R5, acts as a gate pull down resistor holding the device in the off state during the initial power up of the gate driver circuit. With R28,R29 values of 10K and R22 of 4K7 with off-the-shelf npn and pnp transistors (BC547,BC557) the rise/fall times at the output MOS gate is around 250nS for 3A load and 6V supply, for a IRFZ44N MOSFET. On the other hand using excessively high values will cause a problem with the switching of the MOS gate, because the maximum available output current from the npn-pnp pair will be lesser (lesser maximum base current available etc.). The gate driver is a power amplifier that takes the low voltage from the IC controller and generates drive current for the gate of a high power transistor such. This effect is demonstrated with a 48V to 3.3V step-down buck converter, built around the MinDCet MDC901 gate driver, a GaN Systems GS61008P half-bridge and a WE-HCF 1.4uH/31.5A power inductor, as depicted in Figure 5. If this happens the output npn-pnp pair will conduct simultaneously (in linear mode) and cause heating up and possible burn-out of the pair. This will cause the voltage at bottom point of R23 to hover somewhere between 0 and V+ rail. The circuits involved in this control are collectively named the gate driver. values comparable to R23) then the resistors will cause loading of the previous stage.
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