Isolated feedback in flyback switcher

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

Hi,

mrinalmani said:

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

Click to expand...

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

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.