# How to get single channel power supply variable between +12V to -12V .

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#### drkjreddy

##### Newbie level 5
Hello,

I have a three channel power supply, +5V, +12V, -12V DC regulated developed using LM317 and LM337 ICs. Now I want to have a voltage source that can be varied between +12V to -12V DC. This variable voltage is used for reference/offset adjustment of the comparator circuit.

Kindly help me how to get the variable voltage +12V to -12V by using three channel variable supply.

Kindly let me know circuit design and description any.

with thanks

drkjreddy

#### zuisti

##### Advanced Member level 1
I have a three channel power supply, +5V, +12V, -12V DC regulated developed using LM317 and LM337 ICs. Now I want to have a voltage source that can be varied between +12V to -12V DC. This variable voltage is used for reference/offset adjustment of the comparator circuit.

Kindly help me how to get the variable voltage +12V to -12V by using three channel variable supply.

If the tests of the +12V and -12V supplies are common, simply use a potmeter to get a +12 .... -12V DC.
A comparator input doesn't require considerable power ...

#### drkjreddy

##### Newbie level 5
Thanks for your reply. suppose If I have a +12V and -12V voltage sources and I do want to have a variable voltage source variable between +5V to -5V DC. How can I achieve it. Is there need to have 7805 7905 voltage regulators again at the o/p of 12V and -12V Dc for having a single variable +5 to -5Volts

with thanks

drkjreddy .

#### zuisti

##### Advanced Member level 1
+5 to -5 Volts
how much power is needed?
If you also only need to input of a comparator, sufficient a resistor-divider, the 7x05 regulators are not needed

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