# Basic Transistor Question

**URL:** <https://boards.straightdope.com/t/basic-transistor-question/399602>\
**Category:** Factual Questions\
**Created:** [April 11, 2007, 2:59am UTC](https://boards.straightdope.com/t/basic-transistor-question/399602 "2007-04-11T02:59:30Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Cubsfan](https://avatars.discourse-cdn.com/v4/letter/c/f4b2a3/32.png) [@Cubsfan](https://boards.straightdope.com/u/Cubsfan)\
**Post date:** [April 11, 2007, 2:59am UTC](https://boards.straightdope.com/t/basic-transistor-question/399602/1 "2007-04-11T02:59:30Z")

</div>

If you know Vbe and Vce how do you find Vcb? Isn’t Vce=Vbe-Vcb?

Common emitter, Forward Active by the way.

Thanks!

---

<div class="post-metadata">

**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\
**Post date:** [April 11, 2007, 3:18am UTC](https://boards.straightdope.com/t/basic-transistor-question/399602/2 "2007-04-11T03:18:19Z")

</div>

[QUOTE=Stinkpalm]  
If you know Vbe and Vce how do you find Vcb? Isn’t Vce=Vbe-Vcb?

Common emitter, Forward Active by the way.  
[/QUOTE]  
If by “Vbe”, “Vce”, and “Vcb” you mean the actual voltages(\*) between base and emitter, etc., for a given transistor state, then Vce=Vbe+Vcb. (Remember that Vce=Vc-Ve, where Vc and Ve are the collector and emitter voltages relative to some arbitrary fixed reference. So Vbe+Vcb=(Vb-Ve)+(Vc-Vb)=Vc-Ve=Vce.) This doesn’t depend on what kind of transistor you have, though of course the likely values of these voltages does.

(\*) I just say this to make sure you’re not using tabulated values like the Vce saturation voltage in this calculation; not all of the tabulated values refer to the same transistor state.