Understanding Vb in Transistor Circuits for Scientists

[Femme_physics]

In a transistor...

If a question asks me to find Vb, do they mean the voltage from the base to the ground, or the voltage on the base resistor?

The question I have does not specify, it just says "find the base voltage, Vb"

So I have 2 Vb's and I'm not sure which one they're asking for...

http://img39.imageshack.us/img39/3839/vbbok.jpg

 

[gneill]

Single letter subscripts for voltages usually refer to the voltage of that terminal with respect to ground. Thus V_b (or Vb for subscript impaired documents) would be the potential at the base with respect to ground.

Double letters refer to potentials between terminals. Thus V_be would be the potential at the base with respect to the emitter.

 

[NascentOxygen]

Hi FP! There is a strict convention involving upper and lower case, both for the V and the subscripts. When you are talking about DC (or average) levels, you use capital "V" and capital subscripts, so base voltage would be V_B.

If you were talking about just the AC component (i.e., the audio signal your circuit is amplifying), then you use lower-case "v" and lower-case subscripts, e.g., v_b.

There is more, but if you follow this much you'll be off to a good start.

Yes, V_B is from base to ground.

 

[Femme_physics]

Thanks for clearing it up :)

 

[NascentOxygen]

And if conventions were being correctly followed, there would be only one V_B in your schematic, anyway, so no room for confusion. The other one would be V_RB.

 

[Femme_physics]

Ah...dooly noted :)