# specific voltage offset circuit?

#### coinmaster

Joined Dec 24, 2015
502
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.

#### djsfantasi

Joined Apr 11, 2010
9,188
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?

#### crutschow

Joined Mar 14, 2008
34,844
What is the voltage range of both voltages and what power supplies do you have available?

#### Alec_t

Joined Sep 17, 2013
14,411
The catch is my new voltage reference can't draw any current from the variable voltage source
Not even a few microamps? Can you tell us the spec of this mystery variable source?

#### coinmaster

Joined Dec 24, 2015
502
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?
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.

Not even a few microamps? Can you tell us the spec of this mystery variable source?
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.

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#### coinmaster

Joined Dec 24, 2015
502
Did someone have an idea?

#### ErnieM

Joined Apr 24, 2011
8,382
A seccond -6v floating source would do the trick.

#### djsfantasi

Joined Apr 11, 2010
9,188
Like post #2 suggested

#### mcasale

Joined Jul 18, 2011
210
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.