Switching center

[walker1]

I have an input voltage at 48-54VDC and I would like to convert that to +/- 24-27 VDC.
The currents involved in either or both voltages can be anywhere from 0-3.5 Amps.(I.e. the currents are not always the same in both channels)

A standard OP-Amp controled linear power stage can do it, but I find the power loss too great.

Does anybody know how to make a switcher, that can do it ?

Walker

 

[nbucska]

Yes. How much noise/variation can you afford ? <nbucska@pcperipherals.com>

 

[walker1]

Noise is not that big an issue.

The main users on the dual voltage system will be electromagnetic devices, so say 1 V ripple should be acceptable.

In the meantime I have so far come up with 2 possible solutions on my own.

1
A totem-pole driver switching the 50V at 50% duty-cycle and then an LC-filter to the center &quot;0V&quot;

2
Switching the 50V down/up to +/- 4V from the &quot;0V&quot; center and do it linear from there.

 

[nbucska]

If it is for EM devices, you can use the 50% duty cycle
squarewave directly -- no filtering is needed.
If the frequency is high enough, you can have very
low current ripple value.

You don't need totem-pole -- one-sided switch is OK.
<nbucska@pcperipherals.com>

 

[walker1]

As I will need to both sink and source current through the center line, I still think a totem-pole drive is in order.

Also some sort of a filter is in order, as I will have fairly long connections to the various devices.
(radio noise from the wires)

 

[electricuwe]

You will get an very effiecient solution when you use a charge pump design. Take a look at the opeation of one of the numerous charge pump ICs and try to design a circuit operating in the same way at the power level you need using discrete Mosfets.