# Trying to design a power unit to get 4 level voltage output

#### chamal1996

Joined Oct 7, 2020
12
I want to get -32V , -12 V , +12 V and +32 V (all are DC ) from 4 terminals ( simultaneously ). Any suggestions, please?
I tried to achieve these levels with 4 DC to DC boost converters but it didn't work.

#### Attachments

• 13.2 KB Views: 11
Last edited:

#### ericgibbs

Joined Jan 29, 2010
19,100
hi,
What are the required current levels for those outputs.?
E

#### LesJones

Joined Jan 8, 2017
4,226
I SUSPECT that you problem MAY be due to the fact that most boost converters have a common negative rail for input and output. You will need to post the schematic of how you have wired them together and the information on the converters.

Les.

Last edited:

#### crutschow

Joined Mar 14, 2008
34,841
You will either need isolated converters or ones designed to generate both positive and negative outputs to get both polarities.

#### LesJones

Joined Jan 8, 2017
4,226
Or rectified input from three isolated windings on a a transformer. (Or three transformers)

Les.

#### crutschow

Joined Mar 14, 2008
34,841
Or rectified input from three isolated windings on a a transformer. (Or three transformers)
Why three?
For non-isolated converters he would just need one for the positive voltages and one for the negative voltages.

#### LesJones

Joined Jan 8, 2017
4,226
If he just had one isolated negative supply the most negative output would be connected to the negative of both buck converters. The positive of this converter would be connected to the common output terminal. So the negative of both converters would be at -32 volts. So for the positive of the other converter output to sit at -12 volts with respect to common it's output would have to be set to 20 volts. To draw current with a load between common and the -12 volt terminal the regulator would have to SINK current rather than supply it. A buck regulator is not capable of doing this. If buck regulators with a common positive rail could be obtained then just two isolated sources would work. Although buck regulators with a common positive rail could be designed (And I think I have seen switching regulator ICs for this purpose.) I have not seen any buck regulator modules of this type.

Les.

#### crutschow

Joined Mar 14, 2008
34,841
With two isolated secondaries you can use one for the positive voltages and one for the negative voltages.
You don't even need negative converters for the negative voltages.
You can build both outputs with the same converters, and just ground the positive output to get the negative voltage at the normally common line. The external load won't know the difference.

#### LesJones

Joined Jan 8, 2017
4,226
What are you going to connect the negative connections of the two buck regulators for the negative outputs to ?

Les.

#### crutschow

Joined Mar 14, 2008
34,841
What are you going to connect the negative connections of the two buck regulators for the negative outputs to ?
Because the windings are isolated you can connect it to whatever you want.
The buck regulator has two connections, one plus and one minus.
You can connect either one to circuit common to have either a plus or minus supply.

#### LesJones

Joined Jan 8, 2017
4,226
I do not agree with your reasoning. The negative of each converter must be connected to a negative supply. As you only have one raw negative supply available you can only connect one of them to it. Remember one converter negative output (Which is common with it's negative input.) had to be at -12 volts with respect to the common output terminal. The other converters negative has to be a -32 volts. So they both can't be connected to the negative of the raw negative supply. Try drawing it out on paper.

Les.

#### crutschow

Joined Mar 14, 2008
34,841
I do not agree with your reasoning.
You are correct.
It won't work with more than one positive regulator per negative output per isolated winding.

#### BobTPH

Joined Jun 5, 2013
9,265
If, however, you can find a negative output buck converter, you can make it work. A simple buck boost converter has a negative output referenced to the positive supply, so you can use these for the negative regulators.

Bob