So recently, i have been studying transistors.. I seem to grasp everything, but i cannot understand one thing.. Im quote one guy's message it might help yo to understand what I am asking...
In BJT saturation mode there are very high excess minority carrier levels in the base resulting in a lot of diffusion current across the CB junction. Yes it’s true that the drift current is in the opposite direction, but the diffusion component is larger and so the net current is actually opposite to the electric field direction. Remember that diffusion current is driven by concentration gradient (and thermal motion) so yes it is possible for diffusion current to flow counter to the electric field!
I dont understand how current flows in transistor when its in saturation... If both junctions are forward biased and assuming the current flows from p (+) to n (-) we should have that current flows from base to collector, but as i was reading articles about transistors, everyones says that current flows frrom collector to base, and then get through the base to emmiter because the layer is so thin and etc...
In BJT saturation mode there are very high excess minority carrier levels in the base resulting in a lot of diffusion current across the CB junction. Yes it’s true that the drift current is in the opposite direction, but the diffusion component is larger and so the net current is actually opposite to the electric field direction. Remember that diffusion current is driven by concentration gradient (and thermal motion) so yes it is possible for diffusion current to flow counter to the electric field!
I dont understand how current flows in transistor when its in saturation... If both junctions are forward biased and assuming the current flows from p (+) to n (-) we should have that current flows from base to collector, but as i was reading articles about transistors, everyones says that current flows frrom collector to base, and then get through the base to emmiter because the layer is so thin and etc...
The way I think about BJT saturation is that two things are happening at the same time:
- the transistor is acting as a transistor, so the base-emitter voltage sets a collector current and this in turn sets a required base current
- at the same time the collector-base junction is acting as a forward biased diode so in a sense this is stealing base current and so reducing base-emitter voltage
There are others on here who know far more about this than I do.
- the transistor is acting as a transistor, so the base-emitter voltage sets a collector current and this in turn sets a required base current
- at the same time the collector-base junction is acting as a forward biased diode so in a sense this is stealing base current and so reducing base-emitter voltage
There are others on here who know far more about this than I do.
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