Transistors in Parallel

Why connect transistors in parallel? Connect in parallel to handle high currents Need to be closely matched for equal current sharing. Connect resistors in series with the emitters to get 45 to 55% current sharing.

Dynamic Current Sharing

Consider an increase in I E1 If I E1 increases, –L 1 (dI E1 /dt) increases Voltage L 2 (dI E1 /dt) increases, increasing current I E2 (shifting, or sharing the increase)

Turn-on and Turn-off times During turn-on,

Turn-on and Turn-off times During turn-off,

Transistor Chopper limits

Approximate Switching Waveforms

Equivalent Circuit at turn-on

Equivalent Circuit at turn-off

At turn-off Q 1 becomes open I L flows through C S, charging it towards V S The capacitor voltage appears across Q

When C charges to V S, D m turns on

Looks like an RLC circuit

Discharge time = T S /3

Insulated-Gate Bipolar Transistor IGBT Gate -- G Emitter -- E Collector -- C

Output Characteristics

Transfer Characteristic

Structure

When V GE >V T – Channel Induced Induced channel

Equivalent Circuit

Driver Circuit