Hi Ratch
I must say what a very good explanation of how a BJT works . I am a bit confused well it don't take much. I was once told in a post that if I wanted to be pendantic then a BJT was in fact a field effect device. I was not sure but ended up using this in a presentation amongst other technical people at work. They looked at me. Bit confused I must say. But thinking I had been educated on here I felt quite confident.It appears they might have been wrong.
If whomever told you that meant a BJT and a FET worked the same way, he was dead wrong. A BJT is a bipolar device. It uses two different charge carriers (holes AND electrons) to make a current. A FET is a unipolar device. It uses one charge carrier (holes OR electrons) to make a current. A BJT controls the collector current by sending it THROUGH or across the base-emitter depletion region that is controlled by the Vbe voltage. A FET controls the drain current by sending it ALONG or parallel to a depletion region formed into a "channel", whose widening or narrowing is controlled by the Vgs voltage.
If this is the case then I am pissed to be honest.
Now this person might have been on about the electric field that is developed between the BE junction that pushes the electrons into the bases neutral region. I am not sure.
So I am now confused about the whole electric field thing.
I keep telling you that it is diffusion that brings the charge carriers into the base region, not Vbe. What Vbe does is lower the barrier voltage so that more charge carriers can diffuse into the base region and be swept into the collector by the voltage difference between the base and collector
I thought that if you had a potential difference you had an electric field between the two so more charge on one side than the other. And in a transistor say the collector is higher porential than the emmiter you have an elctric field between the two so why don,t you have one across the base emmiter juntion which pushes electrons into the base. Then does this not match what Steve is saying.
Your statements and question are not very coherent. I don't know if you are describing a capacitdor or a PN junction. Again, charge carriers are not pushed or pulled from the emitter into the base by Vbe. They are moved by diffusion.
If not can you explain the difference.
I understand that the BJT is a diffusion device and it does not need an electric field to do so. But it does this because of the difference of charge between the emitter and collector. But if this charge difference is a potential difference why is there not an electric field.
Thanks
Adam
What can I say? Diffusion results from the concentration difference of holes and electrons of a PN junction. The P side has an abundance of holes, the N side has an abundance of electrons. They get together on the PN boundary and annihilate each other to form a depletion region.
Ratch