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Flyback Transformer

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khatus:
Hi,

This is Flyback Transformer also called Pulse transformer.Widely used in SMPS circuit.I have some Chinese smps. While i trying to reverse engineering those Smps,i have faced one problem i can not decide which one is primary and secondary,Auxiliary winding.It has 2 lead at one side and 4 lead at other side.Can anybody tell me how to decide primary secondary and Auxiliary winding.And how to determine the dot convention of those transformer??

ArthurDent:
The picture you posted of the transformer looks like a catalog picture. A photo of an actual power supply that you have would be a big help. If you have a SMPS that is all assembled then it should be easy to trace out the circuit. Generally the secondary is much lower voltage and higher current than the other windings so it probably have fewer turns of much larger wire.

khatus:
Actually the smps still working well. I can desolder it.Its a 12V 2A SMPS

Jwillis:
Its dependent on the circuit . Some times a secondary winding falls back to the High side of the SMPS to power the PWM.With these high frequency transformers its much harder to know by the resistance alone because of fewer winding s .Some can have as few as a half winding on a secondary.If its still in circuit the primary will be on the high side (mains input side) and will be tied to the drains of one or more MOSFETS and will have larger copper traces.If theirs a secondary on the high side will most likely be,but not directly , linked to the PWM .All remaining secondaries will be on the low voltage side.Think of the transformer as the border between the high voltage side and low voltage side.

If the transformer is out of circuit and your unsure of the orientation then a arbitrary function generator can be used to find the pin outs of the transformer.If you have a function generator.

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