For high-frequency drivers and driver boards with protection functions, users who wish to test the normal static (no mains power) output waveform should note the following:
1. If the power transistor (IGBT) or MOSFET is already connected to the circuit, apply the driver power supply and PWM input signal, and the corresponding output signal should be visible at the output using an oscilloscope.
2. If the power transistor is not connected and you are only testing the output, the collector and emitter (or drain and source) terminals of the power transistor must be short-circuited. If the collector or drain is left floating, the driver or driver board will interpret the power transistor as short-circuited and activate its internal protection mechanism. The resulting protection signal waveform will be completely different from the input PWM signal in both shape and period. The primary challenge in IGBT applications is providing comprehensive protection against overcurrent, short-circuit, and overvoltage. Overcurrent faults generally take a while to cause the power supply to overheat, so protection for this condition is handled by the main control board. Overvoltage typically occurs when the IGBT turns off. The large di/dt creates a high voltage across the parasitic inductance, requiring a snubber circuit to clamp the voltage or appropriately reduce the turn-off rate. A short-circuit fault instantly generates a very high current, which can quickly damage the IGBT. Overcurrent protection on the main control board is often inadequate, requiring immediate protection from the driver circuit or driver.
