October 9, 2015

Homework Help: Electronics

Posted by Muuusen on Tuesday, March 31, 2009 at 11:25am.

Hey. I have been working on some exercises. It all went well until I got to this one.

The transistor in the picture is an NPN transistor. I know the RC value is missing. That’s probably an error, but as long as an appropriate value is used I guess it doesn’t matter. I just want to understand how this can be solved. The exercise is as follows

1. Draw the Thevenin-circuit for the voltage on the base.

Have done this one

2. Calculate the size of the Thevenin voltage source, VTH, and the Thevenin resistor RTH.

I have problems doing this one. My idea was to calculate the current going through R2 by setting up some equations. Then then the size of the Thevenin voltage would be R2 * I2? The problem is that the transistor makes it difficult for me to set up the equations when it comes to Kirchoff’s voltage rule (loop rule). I only know that the voltage drop from base to emitter is about 0.7V.

3. The transistor has an Hfe = 100. How big will the current IC be? Show the calculation.

Not reached thi sone yet.

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