DC Analysis of BJT

Thread Starter

DCJW

Joined May 18, 2022
11
Hi, I would like to do the DC analysis of the following circuits but thers a problem here, the value of VBB is so high when using the formula (VBB=VEE+(VCC-VEE)RB) because there is no R1 and R2 only RB is given,is it the problem is at the formula or is the value normal ?
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LvW

Joined Jun 13, 2013
1,466
Please, don`t use symbols (like VBB etc) not shown in the circuit.
More than that, explain the formula mentioned in your text.
Otherwise, we cannot comment.
 

Thread Starter

DCJW

Joined May 18, 2022
11
VBB is the base voltage of a bipolar junction transistor, which can be calculated using the formula above which is VBB=VEE+(VCC-VEE)RB then only use these values to calculate the value of IB which is the base current, but then after I found the value of IB there will be a big difference compared to when I do a simulation in LTSpice.

VEE=-5
VCC=+5
β=200
VBE(on)=0.7


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LvW

Joined Jun 13, 2013
1,466
Referring to the first (handwritten) formula:
Did you realize that at the right side of the equation we have "voltage*Ohm=voltage"?
 

Thread Starter

DCJW

Joined May 18, 2022
11
Referring to the first (handwritten) formula:
Did you realize that at the right side of the equation we have "voltage*Ohm=voltage"?
Ya, I now only realize the problem in this formula, Thanks for your advice.
 

Jony130

Joined Feb 17, 2009
5,351
So for this case the emitter current is Ie = (5V - 0.7V)/(100kΩ/(200 + 1) + 240Ω + 20kΩ) ≈ 0.2074mA ≈ 207.4μA Thus, the base current is 1.032μA which means that the base voltage will be very close to 0V (-103mV).
 
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