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AC to DC Power Conversion - Capacitive Bleed

Transformer-less Power Supply for Microprocessor Based Mains Projects

Some time ago a friend I of mine asked If I could fix his Martec remote controlled fan. I said they are cheap now but apparently they are not common with an IR remote. I said I would have a look and this resulted in the circuit you see.

At this point I must stress that this circuit is LIVE and could KILL you when plugged into 240VAC. Although the processor itself runs off only 5V the entire circuit is referenced to Active 240VAC and is as such LIVE / deadly. This configuration is not for the beginner and a sound knowledge of mains electricity is required before even touching such things. LIVE projects are for experienced people and a mistake will result in either a bad shock, death or a big bang and a lot of smoke. I do not recommend anyone recreating the circuit as it represents what was done more than what should be done. As usual, and especially with this one, any pain damage death or injury is not my responsibility. I said don't do it, I know I wouldn't.

At first I was a little bewildered and double checked to see if I got the circuit right, apparently I did A little research on the net revealed some reference to the configuration as a "Transformer-less Power Supply". A low voltage rail supplying up to around 30mA is possible without transformers or complex switchmode designs. This is adequate for most microcontroller circuits to happily run off.

At a best guess this is how it seems to work:

The simplicity of the design was intriguing if somewhat dodgy and dangerous. Remember this was a commercial 240VAC appliance made in China. Nevertheless I replaced the resistor with some handy carbon types available and as far as I know it still lives.

The circuit was designed primarily for 240VAC operation however I cant see any reason why it wouldn't work from 120VAC The principal of this design could be used to power a PIC mains based project however double insulation between all switch contacts is mandatory. Also there can be no leads attaching anything you can touch without appropriate isolation devices in place, infra red is not a problem. Careful design consideration must be used if contemplating such a configuration. Having said that the bonus is a design that uses virtually no power and emits little heat, also there are very few parts.

See also:


file: /Techref/power/ACcapbleed.htm, 4KB, , updated: 2014/10/8 18:15, local time: 2017/11/20 01:46,
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