I am designing a clamping circuit for an IGBT driver such as ABB 5SNA 0600G650100.
Between the collector and the IGBT gate there will be a set of TVS diodes with a Schottky diode at the end. The gate will have a 6.8k pull-down resistor to the emitter and a protection Schottky diode connected to the +15V (positive power supply to the driver). The negative power supply of the controller is -10V. The second loop of the clamping circuit will be connected to the driver to control output stage. When a clamping event is detected, the controller output will switch from the off state to the on state.
I'm not going to use a resistor in the clamping circuit. My guess is that when clamping, excess power will be delivered and dissipated in the power circuit. Due to the second loop, during these events the controller will be already in on-state.
If we assume Rthja = 68°C/W, operating temperature = 65°C and maximum operating temperature = 175°C, then the maximum allowable power per diode is (175-65)/68 = 1.62W.
How to estimate the average power in clamping circuit and get information about the necessary number of TVS diodes and the maximum Vrrm voltage of each diode? What type of TVS diode should I use?
I want to use as few low Vf TVS diodes as possible. This is crucial when designing a saturation monitoring circuit.
