# Split rail DC/DC converter

The input voltage of my system is ±15V. I need to generate the ±5V voltage. As I need it to power precise analog components (ADC, op amps), my plan is to use DC/DC converter for reducing it to, lets say ±7V, and than to use linear regulator (like LT3032) to get the required ±5V (as linear regulators in general have lower noise). As total current of my system is about 1A, I would avoid solution with only linear regulators because of substantial dissipation. However, I am not sure how to implement DC/DC conversion for negative rail. I know that there are options for supply inversion (make negative rail from positive), but it seems (maybe I am wrong) that those inversion rails circuits are usually for currents less than 1A. And those circuits only use positive rail, although I have also the negative one coming to the system. I saw somewhere schematic with two (non-isolated) DC/DC converters, connected like in the following figure, but I am not sure if this is possible (at least work for higher currents)? Please suggest what would be the proper solution.

• You should use isolated dc/dc converters for this. Commented Oct 7, 2019 at 13:22
• Hint: non-isolated means the input ground is connected to the output ground. Commented Oct 2, 2020 at 11:10
• Not possible use, 7805 and 7905 with a voltage divider based circuit .. every V+/V- will be less than a half of the Vin (simply (Vin-2V)/2).. Commented Nov 27, 2020 at 9:10

Yes but redrawn looks like this.

simulate this circuit – Schematic created using CircuitLab

If done with 1 IC on a custom PCB it would look like 2 independent circuits with Nch for postive switches and Pch for negative.

Some are independent adjustable, others tracking single control adjustable and others fixed Buck regulators.

You can create a split rail +/-V out also with other IC's that can share 1 inductor but multiple switches inside IC.

PSU AC-DC modules are pretty Cheap to buy these days online < $0.5 to$0.1/Watt and you can get +/-5V free off your old PC MOBO or PSU

Usually an opamp or ADC doesn't need 1A current for negative rail, therefore a charge pump is used. In your application, also two LDOs from +/-15V would suffice.

However if you need dual supply, I would recommend you to use already made DC DC module for that. They come from various manufacturers: Murata, Traco Power, TDK Lambda, Recom, ...many others. You can choose from non-isolated or isolated types. It will save you lot of work and testing.

Easy with switching supplies. It's called buck-boost, can be done in a few ways.

What you draw is a plain buck DC/DC plugged as a negative converter. Output goes to GND and VSS goes to the negative rail.

Just be careful, input and output voltages sum up, so mind absolute maximum ratings.

Of course, there are specialized buck-boost converters, though some times it's better to reuse same components you already have in the system.