[AMRadio] Voltage regulator

Donald Chester k4kyv at hotmail.com
Sun Mar 19 10:24:09 EST 2006

>If its just relays, you can just add say a 5 ohm resistor
>on the output.
>measure the voltage with the relays pulled in, load/no load
>voltage will vary a lot...
>Or, if its DC, reduce the filter cap a lot, you don't need
>filtering for relays, and the size of the cap has a big impact
>on the loaded voltage you get out.
>Or, add choke input,
>Or, half wave rectify the thing, gives half the voltage output
>(use a big cap), 8 and 18 volts may pull the relays in fine.
>The three term regulators are mostly good for 1.5 amps,
>there are adjustable ones and fixed ones, I don't think the fixed ones
>have any additional parts...input, output, ground?

One problem with the pass transistor circuit is that if the transistor craps 
out, you can have full output voltage from the filter cap delivered to the 
output.  It probably wouldn't hurt  the  relays for a short period, but it 
would toast many other circuits designed to run off 12 or 24 volts.  To be 
really safe, it would be advisable to add a "crowbar"  circuit that would 
short out the power supply and blow a fuse in case of excessive voltage 
output due to regulator failure.

Don k4kyv

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