Transformerless Power Suppply

[Melanie]

The VDRs (aka Varistors) we use are made by Joyin Co of Taiwan. They work out between 5-15 cents (US) each depending on the flavour. If finding Joyin is a bit elusive in your neighbourhood, then push this link...

http://www.motionnet.com/cgi-bin/sea...?a=cat&no=2149

[T.Jackson]

Early last year I designed mark II of my PC-Controlled Mains Switch. As with the original design, I opted for a transformer-less solution. 240VAC directly feed to three paralleled X2 class rated caps, then to a full wave bridge powering two shunt regs to produce 5, 12V rails respectively. The entire circuit is optically isolated from the PC at all times.

During development of the Windows-based software which drives it, one of the opto's shorted when my multimeter probe slipped. This turned out to be disastrous! It took out the entire parallel port on my notebook weighing in at the time around $3,000 !!! &*@!()K

The paramedics managed to revive me after several hours. When I came to, had a beer and faced the inevitable reality of my "accident". The notebook was sold at a bargain price to someone who wasn't terribly concerned with the absence of the parallel port.

The project was finally completed on a desktop PC and published in the Silicon Chip magazine last July. Unlike the first version, it was a complete flop. No kits were produced. Double the features but twice the price to build. The system is easily expandable - (up to 8 units can be daisy chained together) - Windows-based software to boot, undoubtedly there will be no MK III, and I'm certainly in no rush again for a cost-effective transformer less solution.

*Always take extreme care when working with mains power!

http://www.siliconchip.com.au/cms/A_107104/article.html

Best regards,
Trent Jackson