# Diode Clamp question

Discussion in 'Homework Help' started by Cue Cue, Nov 26, 2008.

1. ### Cue Cue Thread Starter New Member

Sep 25, 2008
4
0
I am having trouble with one of my questions from my lab. I need to design a circuit with silicon diodes to limit the output voltages across a 2M ohm resistor to a max of 3.5 V and a minimum of -0.7 V. and then I need to choose an R load to limit the power dissipation in any diode to less than 500 mW when Vin is + or - 100 v

I have the question and the first part of the question that Ive done so far in the .jpg file attached to this post

I need help on figuring out what value of Rload i should make so that i can limit the power dissipation in any diode to less than 500 mW when Vin is 100v

I was told from someone at school about turning the circuit into a thevenin equivalent circuit but Im a little confused in how to go about doing that can someone please help figure this out.

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2. ### eblc1388 Senior Member

Nov 28, 2008
1,542
102
In real life, there is no 2.8V source for you to connect your diode to to limit the voltage at 3.5V across the 2M load.

You know about the forward voltage drop of a single diode, how about multiple diodes in series?

The forward voltage drop of a diode can be considered to be 0.6~0.7V in your case, so it is easy to determine the max. current such that the diode power rating does not exceed whatever required limit. Pw=V*I.

If you know the diode current then you can work out the series resistor value.