# specific voltage offset circuit?

Discussion in 'General Electronics Chat' started by coinmaster, Apr 9, 2016.

1. ### coinmaster Thread Starter Member

Dec 24, 2015
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6
I have a variable voltage source and I need to have a voltage reference that is always -6v relative to the variable voltage source.
The catch is my new voltage reference can't draw any current from the variable voltage source in order to get its voltage drop but I must be able to draw current from the new voltage reference itself.

I can't think of any ways to get a -6v offset without drawing current from the variable voltage source via LEDs or something.

2. ### djsfantasi AAC Fanatic!

Apr 11, 2010
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What is the required variable voltage range? Is zero volts necessary!

Could you place a second voltage source of 6VDC in series with your variable voltage source?

3. ### crutschow Expert

Mar 14, 2008
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What is the voltage range of both voltages and what power supplies do you have available?

4. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,804
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Not even a few microamps? Can you tell us the spec of this mystery variable source?

5. ### coinmaster Thread Starter Member

Dec 24, 2015
350
6
Variable voltage range is 0- -300v but in practice it will never go above -50 or below -150.
I could put another voltage source in series. The variable voltage source draws from a -300v supply, all I need to do is have another supply that is -6v relative to the variable one. Oh and when I say -6v relative to the negative variable supply I mean I want it to be more negative, not a double negative.

A few microamps would be fine, just not miliamps.
The essence of the variable voltage source is just a source follower being fed by a bunch of opamp circuity which is being fed by a -300v supply.

Last edited: Apr 9, 2016
6. ### coinmaster Thread Starter Member

Dec 24, 2015
350
6
Did someone have an idea?

7. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,394
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A seccond -6v floating source would do the trick.

8. ### djsfantasi AAC Fanatic!

Apr 11, 2010
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Like post #2 suggested

9. ### mcasale Member

Jul 18, 2011
210
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Maybe I missed it, but what is the application? From the high voltage it sounds like it could be an electric vehicle of some sort. Anyway, you may want to think about isolation between the high voltage stuff and anything a user might come into contact with.

EVs do have some requirements for safety, but I think they are still in process.