Modified a flyback tranformator to dual forward

[Rembulan]

Hi every one,

I like to learn about SMPS and for start I like to use CM6800 chip for controller but I have no idea where to find the suitable core to start and I found in my local market there is many SMPS use to replace flyback converter in TV set and my question is how or where I can find formula to convert an flyback converter to a dual forward converter.

[Rembulan]

any one have an Idea about this

[Iain McNeill]

Not an expert in this field but I suspect there are fundamental problems to doing this. A flyback converter uses an inductor while a forward converter uses a transformer. Inductor cores are usually gapped due to the high energy stored in the core while transformer cores aren't.

You'll need a lot of turns on an inductor core to get a decent transformer which will increase resistance and hence losses. I think this just gets you the worst of all possible worlds.

[Rembulan]

Originally Posted by Iain McNeill

Not an expert in this field but I suspect there are fundamental problems to doing this. A flyback converter uses an inductor while a forward converter uses a transformer. Inductor cores are usually gapped due to the high energy stored in the core while transformer cores aren't.

You'll need a lot of turns on an inductor core to get a decent transformer which will increase resistance and hence losses. I think this just gets you the worst of all possible worlds.

sorry I think you misunderstanding my post I am not talked about the Flyback in TV st to produce the HV supply but the PSU for all electronics component inside TV set use Flyback topology and the PSU I talked about is use transformer that is big even bigger than my 750 PC PSU

[Iain McNeill]

Can you show some schematics of what you are proposing?

[Rembulan]

here the picture one of the PSU I talked about, its use UC3842AN and follow standard datasheet shematic sugestion, this is a small one they suggest to use it for 14 to 17 Inch TV

[Iain McNeill]

OK, I still don't understand what you are trying to do.

[Rembulan]

The PSU I show to you use UC3842AN with Flyback topology

I would like to use CM6800 with dual forward converter topology

what I need to know is how to convert the transformator use in flyback topology to dual forward topology,

let say in flyback the primary use 100 turn and 38Khz freq now how to calculated the turn needed in dual forward let say use same freq.

is this clear enough ?

[Iain McNeill]

You need to determine the Al value of your core which tells you the inductance you get for the number of turns.

Number of Turns required = SQRT(desired inductance in mH / Al) * 1000

Wind 20 turns on the core and measure/calculate it's inductance, then you can work out how many turns you need. But as I said, the flyback core will be gapped with a low Al meaning you'll need 100's of turns to get an efficient transformer. May not fit on the bobbin or it may have too much resistance for your desired power level.

You will also have to consider the range of input voltages, the output voltages, peak power to be able to determine the flux in the core and so the number of turns and of what gauge wire. But the datasheet/application notes should have all that design information for you.

[Rembulan]

seem no fun at all, I think its better to me to collect defect PC PSU to find the core I need at least I will not dealing with a gapped core like you say, maybe I can double the core and made my own bonbin can I ?