About Triggering Circuit.The meaning of IGBT, MOSFET & Power Transistor is to switch on the concerning components. Switch on means in the case of IGBT collector to emitter should fully internally shorted i.e. voltage between emitter and collector should be almost zero or few milli volts and in the case of non triggering conditions emitter to collector internally totally open circuit. In the field the requirement is to operate many or atleast two IGBTs at a time. To make proper electrically isolation in between triggering pulses is required here we will be discussed the same. Such type of triggering circuit is use for Mosfet and for power transistor more current is required so driver amplifier is used to drive the power transistor.
Gate Frequency Generation.To operate Gate wave circuit +5 V DC is developed through diode D1, D2, D3, D4, C3, C4 and IC 5. IC1 is a stable multi vibrator VR1 to control its frequency. It will give the output from pin no. 3 and fed to IC2 that is JK flip-flop and its output will come through pin no. 14 & pin no. 15.The frequency at 14 and 15 will half the a stable multivibrator fre- quency. The output from pin no. 15 will feed to opto coupler IC3 and output of opto cou- pler is fed to driver transistor T1. The output of T1 will fed to the base of power transistor T2, the process will same as IC3 and T1. The difference between them pin no 15 of IC2 will at 0o and pin no 14 of IC 2 will at 180o.
For electric isolation every opto coupler is required separate isolated 12 V supply, so it also given in diagram.
Triggering of IGBT.To triggering of IGBT, its required emitter to gate voltage approximates 10 V DC. To operate at a time many IGBTs, electrically isolation is required. So its necessary to use opto coupler for triggering of IGBTs at a time with perfect electrically isolation. IGBT is volt- age operated device so voltage with current is not required the gate current almost negligi- ble. The output voltage from opto coupler is sufficient to trigger IGBT.
The gate of IGBT should never hang in air. Because due to available voltage in air the IGBT may partially ON and may heat & damage so its Gate to emitter a high ohmic resistance approximate 10K is hard coupled. The IGBTs is the combination of MOSFET & power transistor to use at high voltage switching.
Triggering of MOSFET.All features to trigger the MOSFET is same as IGBT, only difference is MOSFET is used for low voltage switching. Safety measures 10K resistance is also required. Source to gate voltage approximate 10 V DC is required. Same electrically isolation is required which is operate by opto coupler.
Triggering of Power Transistor.Transistor is current operated device to switching it the requirement is low voltage but few milli amps current also. The output of opto coupler is fed to a driver transistor and transistor will provide sufficient power to a drive a power transistor. Power transistor mostly used for high voltage and high frequency switching.