transformers for cheap low current flyback supply, +/- 45V ?

[Ken Smith]

I'll take a look using my simulator. It would be nice to avoid
regulating the neg rail.

What simulator do you use? What do you do about the AC resistance of the
windings?

 

[mw]

What simulator do you use? What do you do about the AC resistance of the
windings?

It is Tina Pro (Designsoft). I will use one of their transformer
generic models and change the parameters to get "close". I don't expect
anything highly accurate from it, I just want to understand your circuit
better.

mw

 

[Frithiof Andreas Jensen]

Are there any commodity ("cheap and easily obtained") transformers with
which a low power flyback supply might be built? I have used the
Unitrode UCC3843 -style PWM controllers before in a flyback circuit to
get both positive and negative outputs, but always using custom
(expoensive) transformers.

Does anyone have recommendations for a general purpose flyback
transformer? I want to get output voltages of +45 and -45 VDC, at only
10mA or so. Input will be 12V or so.

Epcos, Panasonic, Matsushita, Toko etc. make those things. They are hard to
buy in small lots. The best way is to buy samples or evaluation kits.
..

 

[Ken Smith]

It is Tina Pro (Designsoft). I will use one of their transformer
generic models and change the parameters to get "close". I don't expect
anything highly accurate from it, I just want to understand your circuit
better.

One of the weak points in modeling programs is dealing with the increased
resistance you see at high frquencies. The circuit I suggested gets rid
of most of the cross regulation effects from both the leakage inductance
and the increased resistance. It doesn't remove the effects of the DC
resistance of the coil.

There is a bit of a problem when you go to model it. If you take the
usual tack of increasing the resistance to near its AC value, you will get
too much droop in the unregulated output. If you leave it as the DC
resistance, you will get optimistic results for things like the losses.