Drive Circuit

What is “drive circuit”? Circuits that are constructed to turn on/off power devices/switches Control circuit Gate driver Provides an interface between the control signal (small signal electronics) and power circuits Sometimes called ‘gate drivers’

Why do we need drive circuit? To amplify control signals to level required to drive the power switches and also to ensure fast turn-on and turn-off MOSFET/IGBT typically require voltages between 10V - 20V to ON and initial high current to charge parasitic input capacitance. The capacitor need to be discharged during turn off BJT require continuous current to ON – initial high current is needed to reduce turn on time. Provides electrical isolation between control circuit (small signal) and power circuit Require for safety reasons and elevated emitter (or source) of the transistor in bridge configuration

Some examples of drive circuits Gate drive with totem-pole configuration

Some examples of drive circuits Isolated dc power supplies for drive circuits Opto-coupler isolation Transformer isolation Electrical isolation methods

Some examples of drive circuits Negative half cycle of v s (t) - positive dc rail near safety ground potential. T - emitter potential large and negative with respect to safety and logic ground Postive half cycle of v s (t) - negative dc rail near safety ground potential. T + emitter substantially positive with espect to safety ground if T - is off Variation in emitter potentials with respect to safety and logic ground means that electrical isolation of emitters from logic ground is needed.