That's not really excessive voltage.
Given you have measured the 20V DC (average rectified voltage) at
nominal wall voltage. then you should take some -10 percent tolerance
into account. Another 3 V will be consumed by the regulator, and the
remaining 3V are probably just right to cover the ripple on the
unregulated side. You may use a smaller capacitor, just large enough for
not getting below the minimum regulator input voltage at the lowest
momentary voltage across the cap when your wall voltage is at its low
spec side...
Adrian
Bob Stewart schrieb:
The transformer gives me about 20 volts DC out. Dropping 8 volts at 1 amp is
just a lot of power to void with a resistor. I'd like to avoid having that
much waste heat in the unit. I do have an old power brick, but I was hoping
there was some small switching board that people had had good luck with. Maybe
the brick is the best option.
Bob
________________________________
From: Chris Albertson <[email protected]>
To: Bob Stewart <[email protected]>; Discussion of precise time and frequency
measurement <[email protected]>
Sent: Thursday, June 27, 2013 1:32 PM
Subject: Re: [time-nuts] +12 Volts 1A (plus a bit) supply?
You mean you have to many volts for a 12V regulator to drop> That's easy to
fix, use a resister in series. Make the resister par of an RC filter and cleaner
power in the process.
I use a plug-in power brink from an old notebook computer. I think mine
outputs 15V and then this gets dropped to 12V and 5V with a RC filter and
regulators.
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