# Transistor Biasing and equivalent circuit

#### ZeroBlank

Joined Jan 22, 2017
14
In the

Dual Feedback Transistor Biasing
i cant seem to understand what all the Vcc and Vin are applied, i already know that the Vcc is applied over the the whole wire to the right and to the left,however,what i dont seem to get is how we deal with RB1 and RB2 and on what bases?
why is the current in RB1 = IB + IRB2 when the current of the IRc = Ic + IRb1 ?

I saw this video on youtube showing that the both the base-collector and emitter-base are forward bias,how come there is always one forward and one reverse?

#### BobTPH

Joined Jun 5, 2013
3,095
Those currents are just a statement of the fact that the current into and out of any node must be equal.

Bob

#### hobbyist

Joined Aug 10, 2008
889
why is the current in RB1 = IB + IRB2 when the current of the IRc = Ic + IRb1 ?
The current that flows through RC is made up of the two branch currents, the current flowing through the transistor "(IC)" and the current flowing through RB1, "(IRB1)".

The current flowing through RB1 is made up of two branch currents, the base current into the transistor, "(IB)", and the current flowing through the resistor RB2, "(IRB2)".

If you would like an example of biasing this circuit using the equations in the box, reply.

#### alan01346

Joined Aug 13, 2020
30
If it were possible to figure out definitions/values for everything needed it seems like you could write a fairly simple program that would calculate the rest. It could even be an online Javascript calculator where you plug numbers into boxes on a web page and the results appear on the page so you could do "what if" scenarios. Almost everything is calculated from something else, like Ic = Ib * HFE. To some degree this is what SPICE does but that's not exactly user-friendly to a beginner. I tried doing this circuit a few weeks ago but couldn't come up with a good value for Irb1. Maybe there's already such a page online somewhere.

#### dl324

Joined Mar 30, 2015
12,786
how come there is always one forward and one reverse?
That is one of the 4 modes of operation (active). The others are cutoff, saturation, and inverted.

EDIT: Got me. Newbie resurrected a 2 year old thread...

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#### LvW

Joined Jun 13, 2013
1,228
....i cant seem to understand what all the Vcc and Vin are applied, i already know that the Vcc is applied over the the whole wire to the right and to the left......
Just one question: Do you know the basic function of such a transistor?
Recommensation: For a beginner (like you?) it would be best to use a good book on electronics basics rather than to use you-tube lessons.

#### dl324

Joined Mar 30, 2015
12,786
Just one question: Do you know the basic function of such a transistor?
This thread is over two years old and the OP was last seen over 2 years ago. No one cares. A new member ignored the warning that it was old and resurrected it anyway.

#### LvW

Joined Jun 13, 2013
1,228
Dennis - thank you....