Short circuit protection of IGBTs and other power switching devices

摘要

A short circuit protection circuit for IGBTs and similar power switch devices. Device collector voltage, e.g., desaturation voltage, is monitored to detect rapidly the occurrence of a short circuit fault. The voltage between the power device emitter and the Kelvin emitter terminals of the device preferably is also monitored and integrated to obtain an estimate of the current flowing through the power switch device. Circuit protection is implemented if either the measured collector to emitter voltage exceeds a selected level or the estimated current through the device exceeds a selected level. Upon the detection of the fault, a capacitor in parallel with a zener diode is connected between the power switch gate and ground. Thus, following a fault, the gate voltage is driven quickly to a low level as the voltage on the gate is discharged through the capacitor. The zener diode establishes a clamp voltage at a selected level of gate voltage that permits controlled current flow through the power switching device that is within the capacity of the device so that the device is not damaged. A pre-charged capacitor is then connected between the gate and ground to turn off the power switching device gradually as the pre-charged capacitor discharges into the gate. The voltage level on the pre-charged capacitor is established by a zener diode connected in parallel thereto.