A measurement of the gate-emitter voltage waveform of IGBT in a motor driver circuit

A fiber optic isolation system is introduced for the measurement of active gate-emitter voltage waveform of IGBT(Insulated Gate Bipolar Transistor) in a motor driver circuit. The system is designed for this kind of floating measurement which requires large common-mode rejection ratio(CMRR) at high frequency and common-mode slew-rate(dV/dt). The required performance is analysed by the convolution of the emitter voltage waveform and a impulse response of a high-pass filter which simulates the common mode rejection. Then the experimental results of the gate-emitter voltage waveform measurement are verified. The proposed fiber optic isolation system consists of a battery powered transmitter, a fiber optic cable and a line powered receiver. The transmitter converts an input electrical signal into an optical signal. The receiver converts the optical signal back into an electrical signal. These are connected with fiber optic cable which has two cores. One is used for the signal transmission and another is for the control command transmission. The receiver also works as the system controller. It has the self-calibration function and GPIB interface function