Perfectly right!I'm thinking he wants a physics-based answer.
Papabravo please keep in mind the fact that i am a newcomer in the electronics field.It will be a kind act to give answers which are easily understandable for a neophyte like myself.Equilibrium. The three currents in a transistor must add up to zero. That's KCL. It is the physics of the junctions and the way the materials are fabricated that producses this behavior.
Einstein said :-We have been talking "geek-talk" for many years. I can't remember when I was a noobie (48 years ago?).
So it is difficult and maybe impossible for us to talk to a neophyte.
Like...I'm thinking he wants a physics-based answer.
It was exactly the kind of answer that I thought I was giving. I'm sorry you didn't like it. I have no idea what level of explanation you're prepared to accept. We can talk quantum electrodynamics if you want to.Papabravo please keep in mind the fact that i am a newcomer in the electronics field.It will be a kind act to give answers which are easily understandable for a neophyte like myself.
And also fairly constant over a range of (base-emitter) forward bias voltages, more for some transistors than others. But why?Like...
In an unbiased transistor there is a potential barrier that prevents electrons from crossing the junction to get to the other side. A small amount of forward bias changes the height of the potential barrier so that electrons can easily surmount the potential barrier and get to the other side. The current required to support this lowering of the potential barrier is on the order of 1% of the collector current which flows and this constant relationship is true over a wide range of supply voltage and temperatur variation.
Let Na be the concentration of acceptor atoms; Na = 10^15 atoms/cm^3
Let Nd be the concentration of donor atoms; Nd = 10^16 atoms/cm^3
Let Ni be the intrinsic carrier concentration; Ni = 1.5 * 10^10 atoms/cm^3
Let T be room temperature; T= 300 dgrees K
Le q be the charge on an electron; q = 1.602 * 10^-19 coulombs
Let k be Boltzmans Constant; k = 8.62 * 10^-5 eV/degree K
Φ0 = (kT/q)*ln(Na*Nd/Ni)≈.63 Volts
Go for it, but don't generalize too much, because lots of transistors do NOT have constant beta vs collector current. I suspect geometry and doping are the primary factors (are there others?).Getting to the Ebers-Moll equation takes more than a little bit of background. That was just the warm up. Are you ready for a long haul?
Please do not reply to a old thread, specially it is 7 years ago, this thread will be closed.Hi
I read and read and can't figure out how a small current (I_b) can control a big current(I_C) at atoms level, let's say. I know that it is in function of the doping level and geometry of the junction but HOW? How I_B allows a proportionally I_C current?
The voltage controlled perspective almost make me understand how, except that I can't figure out how changing R_B resistor (and at the same time I_B) we change V_BE, when in the text's this value is fixed at 0.7V.
by Duane Benson
by Duane Benson
by Jake Hertz
by Jake Hertz