Power supply design for low voltage output

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toosmarttc

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We had intended to use a two tap transformer to drop 110VAC or 277VAC to 10VDC to operate a fire safety light. An alternate and lower cost design is to use a large resistor and a capacitor to drop the voltage. However, two separate circuits will be required rather than a single transformer. Overall, the capacitor circuit (even with two separate boards) will be less costly to produce and ship.

Are there any code issues on using a resistor and capacitor to generate a pulsating AC current that is rectified?
 
If the capactior shorts, you have 277V on something meant to be a "safe" low voltage.

At one time, some company(s) marketed a device to connect you TV antenna input to the 120V house wiring (why they thought Romex would make a good antenna is beyond me.) It used a cap to keep the 120V from going into the TV. But eventually, a lot of the caps shorted. Not sure if anyone got hurt, but I'll bet a bunch of TV's bit the dust over it.

Anyhow, I don't think you will get it UL listed without the transformer.

Steve
 
I've been thinking that I might be mistaken IF your design meets certain requirements. Basically, if you design the entire thing as if it were all operating at 277V, you might be able to do this. A "fire safety light" is kind of vauge, and I'm not really sure what you have in mind. But I think you would have to make sure any live parts aren't exposed, even the low voltage ones.

Steve
 
Tom, I suggest using something like an HVAC transformer, which can usually be found with a multi-tap primary. A half-wave rectifier should give you the input to feed a voltage regulator. Of course, we have no idea of the current you need.
 
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