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Power supply/Transformer design - RF Cafe Forums
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Below are the old forum threads, including responses to the original posts.
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Post subject: Power supply/Transformer design.
postPosted: Fri Apr 22, 2005 12:39 am
Joined: Fri Apr 22, 2005 12:22 am
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.
subject: Power Supply
Unread postPosted: Sun May 01, 2005 11:05 pm
It sounds like the clock already HAS a power supply, minus the
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