How is the emitter current kept constant in common base BJT?
How is the emitter current kept constant?


In a common base circuit, we can analyse it by assuming that the base is held at a constant voltage. Then, given that there might be 0.5 volts (approximately) between base and emitter (because it's a forward biased diode junction internally) we can say that the emitter is at a constant voltage too.

This means that if there is a reasonably sized emitter resistor and it is fixed in value then, emitter resistor current is dictated by base voltage minus 0.5 volts (or 0.6 volts or whatever voltage is dropped across the forward biased base emitter junction).


  Do we ignore the early effect, if so then why?


Early effect mainly applies to voltages at the collector and not the emitter and generally we do ignore early effect at the emitter unless it is relevant or important.