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A wall-wart alternative
I finally got tired of replacing the 2 C-cells in a clock with a moving
pendulum, so I measured the current (3 volts at 340 microamps) and built a charge pump like this, viewed in a fixed font: 0.047 uF @400 V || | -----------||---------------------|------------ || | | | | | 3V 120 VAC --- --- to clock ^ _ 0.047 uF @400 V | | || | | -----------||----------------------------------- || I used two caps in case one shorts and for some ground isolation. The diodes are 5.1 V zeners ($1.29 for 2 at Radio Shack) to limit the clock voltage if someone unplugs the batteries. This circuit supplies 390 microamps. I hope to avoid replacing the batteries until their shelf life runs out in 2012 :-) This could be useful for lots of low-power stuff, eg smoke detectors. Nick |
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