# Get Positive and Negative Voltage from Single Power Supply

#### nateolson

Joined Nov 29, 2022
10
Hey everyone, I'm building a theremin and working on the power circuit. I need to split my 12v input into 0,12, and -12v terminals. Below is what I'm currently using. 1 and 2 are respectively the 12v and ground from my 200mA power supply (just a wall wart). Is there a cheaper way to do this? Can it be an IC? I only want to use one 12v power supply.

#### Papabravo

Joined Feb 24, 2006
19,617
That won't work if the voltage between terminals 1 & 2 is a positive DC voltage. I'm curious to know why you think it will.

#### nateolson

Joined Nov 29, 2022
10
That won't work if the voltage between terminals 1 & 2 is a positive DC voltage. I'm curious to know why you think it will.
I'm working off of this document from the 90s, pg. 3. When I found it I thought it was cool because I had thought you would need to tie two bench supplies together to do that.

#### BobTPH

Joined Jun 5, 2013
6,095
That is about as simple as you can get for a ±12V regulated supply.

Edit: But it needs 12V AC in as papa said.

#### nateolson

Joined Nov 29, 2022
10
That is about as simple as you can get for a ±12V regulated supply.

Edit: But it needs 12V AC in as papa said.
That won't work if the voltage between terminals 1 & 2 is a positive DC voltage. I'm curious to know why you think it will.
Ah, I see that it needs to be AC input, says it right there but I missed it - I'd like to just use a wall wart adapter to 12v DC, is there a way to accomplish the same thing from a DC input? This is the full diagram I'm working from:

#### Papabravo

Joined Feb 24, 2006
19,617
You did not look at the diagram on P.3 very carefully. Pins 1 & 2 are connected to an AC Source. A 12 Volt AC source will have a peak voltage of approximately

$$12\text{ VAC}\times \sqrt{2}\;=\;16.97 \text{ V-Peak}$$

The diodes will rectify the peak AC voltage with some losses to provide approximately ±16 VDC with some ripple, which the regulators will convert into ± 12 VDC with very little ripple.

#### dl324

Joined Mar 30, 2015
15,486
I'm working off of this document from the 90s, pg. 3. When I found it I thought it was cool because I had thought you would need to tie two bench supplies together to do that.

#### dl324

Joined Mar 30, 2015
15,486
I'd like to just use a wall wart adapter to 12v DC, is there a way to accomplish the same thing from a DC input?
You could use 2 and stack them; if the outputs are isolated.

#### bassbindevil

Joined Jan 23, 2014
647
If you want to run from a single DC supply, use a switching regulator to make negative voltage. The MC34063 is found inside many car chargers, and can be configured for negative output. I'd make -15V then follow it with a linear regulator to get the cleanest DC. Motorola provided sample layouts in their application notes for that chip (the older revisions have a layout that is dead easy to copy using packing tape and a hobby knife). Or you may be able to adapt the car charger's board to produce negative output with some hacking of traces. You can also buy DC-DC converter modules off the shelf.

#### dl324

Joined Mar 30, 2015
15,486
Here's an inverting regulator circuit using MC34063A.