Gate and Base Drives Necessity 
Driver circuits are operated at very low power levels. Normally the gating circuit are digital in nature which means the signal levels are 3 to 12 volts. The gate and base drives are connected to power devices which operate at high power levels.

There are two ways of  isolating control or gate signal with respect to ground.

·         Pulse transformers
·         Optocouplers


Pulse Transformers
Pulse transformers have one primary winding and can have one or more secondary windings. Multiple secondary windings allow simultaneous gating signals to series and parallel connected transistors. The transformer should have a very small leakage inductance and the rise time of output should be very small. The transformer would saturate at low switching frequency and output would be distorted.
Pulse Transformer Application


Optocouplers
Optocouplers combine infrared LED and a silicon photo transistor. The input signal is applied to ILED and the output is taken from the photo transistor. The rise and fall times of photo transistor are very small with typical values of turn on time = 2.5 s and turn off of 300ns. This limits the high frequency applications. The photo transistor could be a Darlington pair. The phototransistor requires separate power supply and adds to complexity and cost and weight of driver circuits.

Optocouplers Application


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