I am using an inverter circuit to generate -3v@4a from a +12 rail. I would also like to generate a +3v@1amp by using a couple inductor to the -3v winding. I am probably going to need to wind the transformer with coaxial type cable in order toget them to track very closely. Does anyone here have any experience with thus type of arrangement?
regards, Bob N9NEO
How closely? Is this buck-boost (so the +3 will be flyback)?
I've never had a problem with toroids.
Tim
-- Deep Friar: a very philosophical monk. Website:
Thanks Tim, The circuit is an inverter. It has one end of inductor at ground and the other is pulled up to +12v with mosfet. When fet turns off the voltage flys negative and a diode sends it into a cap so there you go. It's a lot like a flyback. I just want to wind a secondary on the inductor. I am trying to get +-3% on both supplies and I expect winding bifilar isn't going to cut it over all of the loads and so forth. I need a very small coax that is good for about 8amps rms to wind the inductor. Coax will give me supreme coupling. The added expense of the esoteric inductor may cost more than a small buck regulator that I could get an amp out of. Buck regulators that will do an amp are about a buck. (Is there a pun in there somewhere). Other option is to wind inductor so that secondary has few more turns than primary and use LDO.
So back to my question. Is there anyone there with this type of experience that may be able to turn me on to a house that can supply high performance coupled inductor? I think that is what I asked for.
regards, Bob
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Huh? Your rectifier drop with 4A and with 1A won't match, anyway. Why does the winding have to be super-matched? It's commonly done to wind a pair of wires (one with green enamel, one with red enamel) for such secondaries when they have matched turns count. The matching is always good when they're wound bifilar like that.
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Yes, Thank you Mister Whit3rd. The problem of course is that the supplies will not track over all load conditions. Bifilar has been recommended to me by my magnetics house and I will try that first. I understand the problem with the schottkys not tracking and I will have to choose them with caution. The others using the supplies are going to expect less than 5% variance in the output over all of the various load conditions. I will probably have to regulate both of the power supplies to some degree by apportioning some of the feedback current from each and possible pre-loading the supplies.
If you only have to make fractions-of-a-volt differences, you could put a small series choke in series with the AC output of the transformer, and use a small DC control current to bring it near saturation, to make a lossless series pass element. It'd either take two, or you'd want to imbalance the turns ratio to ensure which leg needed the retardation.
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