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Power Supply/Transformer Design - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: Power supply/Transformer design.
Unread postPosted: Fri Apr 22, 2005 12:39 am

Joined: Fri Apr 22, 2005 12:22 am
Posts: 3
My father was an electronics engineer, one of his creations being a clock. I know the clock needs about 10 or 11 volts AC, and I believe at 60 hz. After a while this transformer gets really hot, I don't know if it doesn't have enough Amps or just because it is small and in a closed case. The power supply for it was cracked in half and thrown out a while ago. Currently I am running it off an AT&T Answering Machine adapter I found at RadioShack. That gives out about 10 volts AC, and 800 mA. I am not sure of the frequency. The rectifier is on the clock itself, because it uses the AC frequency as pulses to increment the time, then the rest of it works off DC. Long story short, I was wondering how I could design a new power supply, I am not really that good with electronics. I can do it if I had schematics, but I can't make my own, I don't know what parts to use. Are there general design rules to follow to design power supply/transformers? Or is each one especially unique? I may have to play around to get the voltage/amps/frequency just right. Thanks for any help. If there is any other information I could try to find to make it easier let me know. I've tried different kinds of transformers, if I use DC the clock can't count, and it worked with 20 VAC but the DC part of the clock is regulated by a 5 volt regulator, which overheats within an hour and shuts off. The rectifier is 200 PIV. I don't know what other random information you would need. I think I may be able to go even lower than 10 volts, but sometimes the audio part seems to struggle at the lower voltage, I think its safest to stay at 10.
Thanks for any help.


Post subject: Power Supply
Unread postPosted: Sun May 01, 2005 11:05 pm

It sounds like the clock already HAS a power supply, minus the transformer.

So it sounds like all you need is a transformer with enough current capability.

A "wall wart" type of transformer is usually bit wimpy. Try a 12V 2 A transformer, rated at 120V in for 60 Hz operation. These are pretty standard items, and you can get them from mail-order/web stores like Electronic Goldmine, MPJA, etc., or from industrial distributors (try DigiKey or Mouser - most of the others have minimum order requirements), or possibly even Radio Shack.

Transformers don't change the frequency of the applied power, but the efficiency of the transformer changes with frequency - that's why they have a frequency specification.

There are lots of transformers available for purchase, I don't think you want to consider making your own.

Good Luck!

Posted  11/12/2012

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