Isolated feedback in flyback switcher

[mrinalmani]

Hi
We are trying to make a cost effective isolated DC-DC supply using a simple switcher IC in flyback mode. I have seen several AC-DC offline switchers making use of an auxiliary winding of the transformer for feedback. An example circuit is attached below.

My question is
- can we do the same for a DC DC isolated supply? The input voltage is around 12VDC and desired output is also 12V isolated with 100mA capability. Of course I'll use a different IC with an appropriate external switch. I am primarily concerned with the feedback mechanism.
- I am considering TI's MC33063, for the DC DC switcher. It's a general purpose switcher and I am planning to use it in the same way as the offline switcher circuitry above . Is this approach OK for a low voltage DC DC switcher?

Anyone with experience in isolated DC-DC supply please share your opinions.
Thank you

 

[KlausST]

Hi,

can we do the same for a DC DC isolated supply?

The IC is already working on DC input .... it does never know whether there is a rectifier or not....and it does not know whether the rectifier input is AC or DC.

Klaus

 

[treez]

yes you can do it, but if the non isolated winding is on much higher loading than the feedback winding, then the isolated output may dip in volts quite a bit.....ie when it goes from no load to full load and vice versa its voltage will change quite a bit....after all, its not "directly" regulated.

Its only 12v and 100ma......so why not just use an on/off control with a digital isolater to feed back?....or an opto to the same effect.