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Transformer heats up and hums

Posted by: mike_mccrady on
I had a transformer built by rtss that is designed for 6.7VDC @ 25W (85-285VAC). At a one amp load (7W), the transformer has an audible hum and gets rather hot after about 20 minutes. The output filter caps also get warm to the touch. I have a similar design (stacked FET) for 6.7VDC @ 7W (85-585VAC) with a transformer built by ICT that uses the same output filter that runs cool all day and has no hum. I have included the schematic. I would have attached the transformer design file, but the web site will not take the ".plxtp" file format.

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Power Supply 25W Schematic.pdf 44.19 KB

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Submitted by prasun on 08/28/2008
hi mike..(1) change snubber circuit, refer any PI reference design using zener clamp. Also use p6ke180A. (2)opto coupler pin configuration are completely wrong. check data sheet of opto. (3) use 1K resistor for R4. (4)Take feedback of zener before L1. i hope this could optimise your design. moreover for heating., after all these correction, pls let us know. mail me at prasunkuls@hotmail.com
Thanks, I'll get the parts and see what happens. The other design that I have, uses the same opto setup without any problems. I may have to change that also to match. I'll get back to you with the results.
I just looked at the board and the schematic is wrong. I don't know what happened to that. the pinout on the pcb is right. This I'll have to look at to see where it went wrong. Thanks.
Submitted by prasun on 08/29/2008
mike...opto connections are wrong