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Identify replacement for high frequency transformer

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Hello All...good day...have frequently encounters a switching power supply having faulty high frequency transformer. Most of faulty transformer found was customized and/or doesn't have any markings. Very hard to identify replacement. Can anyone help me please, shares any effective method to identify replacement for high frequency transformer? Thanks.
 

Hi,

it is no easy task:

You need to know two of these three items:
* primary inductance: L(p)
* secondary inductance: L(s)
* winding ratio: n(p) / n(s)
They depend on each other with: L(p) / L(s) = (n(p) / n(s))^2


additionally:
* Voltage-time product "Ut"or saturation current (and it´s definition)
* both winding resistance R(DC) for power loss
* and best the core material ( for frequency selection)

Usually you are not able to get all these values from a broken transformer, therfore it is hard to do.


Klaus

Edit: It --> Ut
 
Last edited:

chuckey said:
How do you know the transformer is broken?
Click to expand...

Got two power supplies with different failures...swap the high freq xformer. If we don't have 2nd unit then we send it for external repair. But they also complained same thing. By the way Chucky, do you have useful method to 100% confirm high freq xformer is defective? I know only continuity check. Thanks.
 

Connect a square wave generator to the primary (or the cal output from a CRO). if you view the waveform, it should be a series of decreasing sine waves at a high frequency. if it has only one major narrow pulse it means that a winding has a short circuit on it.
If you have a variable frequency source, setting the frequency to the operating frequency of the transformer, it should act like a transformer i.e. each winding should have a voltage on it proportional to the number of turns.
Very high voltage windings are made with very thin wire and are extremely unreliable, the line output transformers in old fashioned CRT type televisions were responsible for about 10% of all their faults!!
Frank
 

Yes we have function generator to be a frequency source but a concern is how we can identify the operating frequency of those transformers that don't have markings. Thanks a lot.
 

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