Wednesday 16 July 2014

transistors - Is BJT a Voltage controlled device or Current controlled device?


I have searched already for this question, but everywhere I see debate instead of clear answer. Though it is not that important of a matter whether we call it a voltage controlled device or current controlled device. I believe it can be called both voltage controlled or current controlled depending on the situation. Still I believe it requires a little clarification. Which part it really is in view of the core operating principle?



Answer



The answer depends on your perspective.


A physicist might say that the fundamental action in a BJT is that an electric field across the base-emitter junction decreases the width of the depletion zone. It is this electric field, measured in volts, that controls the movement of charge carriers. Therefore the BJT is voltage controlled.


An electronic engineer might say that the most useful model for a specific circuit design is the current-amplifier model.


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