Maker Pro
Maker Pro

Calculate Transistor Parameters

electronicsLearner77

Jul 2, 2015
233
Joined
Jul 2, 2015
Messages
233
I need to calculate IB,IE and IC with Alpha(DC) = 0.98 for the below circuit
upload_2020-11-29_11-24-52.png
I generally did problems with some base resistor and collector resistance and here i don't find both. I did the following attempt
Since VBB > 0.7V the BE is forward biased (current required?)
If i consider the resistance RE as coming in series with the BE, then the current
IB = (2 - 0.7)/1kΩ = 1.3mA
From alpha = 0.98, beta = (alpha / (1-alpha)) = 0.98/0.02=49.
IC = beta * IB = 49*1.3mA = 63.7mA;
IE = IC + IB = (1.3 + 63.7)mA = 65mA.
Vcc - Vce = IE*RE ; Vce = Vcc-IE*RE = 10 - 65 = -55. Vce seems to be very high!
 

Nanren888

Nov 8, 2015
623
Joined
Nov 8, 2015
Messages
623
Your instinct that something is wrong is correct.
.
If your first equation gives you the voltage on the emitter resistor, then this is the voltage, hence relates to the total current through it. This tells you the total current throught the resistor being a combination, addition of the base-emitter current and the collector emitter current. That is, all that current does not come from the base. Your gain calculations tell you the ratio of currents from each source.
.
If you prefer, the two loop currents which both flow through the emitter resistor, must add to the emitter current you calculate from the voltage.
Let us know how you get on.
 

electronicsLearner77

Jul 2, 2015
233
Joined
Jul 2, 2015
Messages
233
Thank you, that really helped. So,
VE= 2-0.7V= 1.3V;
IE = 1.3/1k = 1.3mA;
IC = Alpha * IE = 0.98*1.3mA = 1.274mA
IB = IE - IC = 0.026mA
Vce = 10 - 1.3 = 8.7V
 
Top