Dual output FLYBACK (bipolar) from a single winding

Hello,

I need an isolated dual output converter (+15V, -7.5V) from a 12 V supply. For design reasons* I would like to use a flyback converter with a single secondary winding. Is it possible to have a dual output using a single flyback winding?

I know it is possible to do so in push-pull converters with a capacitor + diodes circuit see attached file
Source: http://www.mouser.com/catalog/specsheets/6ED100E12-F2_EVAL.pdf[/url] figure 33.

Any suggestion would be appreciated.

Thank you!


*For component reuse and cost I would like to use a flyback converter and transformer (already used in other parts of the system).

you have to use a one reverse biased diode and to use regulator to get the -7.5v

A bipolar dual output or voltage doubler configuration can't operate in flyback mode. It's mixed forward/flyback. The voltage ratio of both outputs will respectively vary with converter duty cycle and probably output load. You didn't mention the intended voltage control scheme and accuracy requirements, so we can only guess about design feasibility.

As far as I can see the design you posted isn't for a push-pull converter, it's just a transformer-coupled charge pump, which is very different from typical SMPS which use inductors for energy storage. The circuit has a fixed duty cycle of 50%, and just functions as a voltage multiplier. The reason it can work with that circuit is because the ratio between the two outputs is an integer, so getting +15 and -7.5 should also be possibly with the same approach. But keep in mind it has no feedback or control, so there's no regulation of the output voltages.

It's possible to get two outputs off of a single flyback winding, if the winding has at least one extra tap, but the output voltage will depend on the duty cycle and load, like FVM states, and thus some amount of feedback is likely required.

Thank you for your comments.
FvM: An unregulated output is acceptable for this (low power) application. I will use a fixed duty cycle and add linear regulators to the positive and negative outputs.
mtwieg: You are right with the observation. I think I will try reusing the flyback transformer but use it as a transformer-coupled charge pump.