Mystery transformer

Thread Starter

k1ng 1337

Joined Sep 11, 2020
681
Hi, I opened an older battery charger to see what components could be reused. The transformer in question appears to be part of a pulsed DC flyback converter as it is placed after the full wave rectifier. I would like to reuse this transformer as a low power 120V/60Hz step down transformer for another project drawing no more than 5W.

There are about 40 components so I am going to undertake the challenge of reverse engineering the board though it will take some time. In the meantime, information about the transformer in the photo would be helpful. There are 3 leads on the primary windings and 4 leads on the secondary windings. I suspect one pair of the secondary windings is used for feedback. What about the primary? Also, there appears to be a capacitive dropper in the circuit as all components are present, what's that about? Given the transformer has no markings whatsoever, what can we conclude about it?

As always, thanks for the read.
 

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Sensacell

Joined Jun 19, 2012
3,064
Forget using the transformer at 60 Hz.
These transformers are designed for operation in the 10's of KHz range, with very low inductance values relative to a 60 Hz transformer.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
681
Forget using the transformer at 60 Hz.
These transformers are designed for operation in the 10's of KHz range, with very low inductance values relative to a 60 Hz transformer.

It is immediately obvious now that you point it out! What if I were to adjust for this change in impedance? Easier said than done I'm sure :p
 

Ian0

Joined Aug 7, 2020
6,286
Make a note of the part number of the 8-pin IC, and find its datasheet.
That will probably tell you the operating frequency.
The primary will probably be Connected to 3 pins as it is wound it two sections and the extra pin used to join them together. just regard it as a single winding. Feedback is usually from the output via an optoisolator. A third winding (which is wound on the primary side) is the auxiliary winding to power up the circuit once it is running. The capacitive dropper probably powers up the circuit to get it started.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
681
The chip is a OB2354 'Current Mode PWM Power Switch' operating at 50kHz. It looks like the chip can be used along with the other components to construct a flyback SMPS minus the battery charging functions.

Any concerns converting this charger to a power supply?
 
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