If you use zener diodes, they must be capable of carrying the full load current of the mains operated device. You may need to allow 10-15 amps, which could be a very expensive zener diode Regards, Harry ----- Original Message ----- From: "Matthew Brush" To: Sent: Thursday, June 03, 2004 5:02 AM Subject: [EE:] Transformerless PS w/o Zener? > Hello all, > > I'm making a current monitor for the mains power line. I plan on using an electrical outlet as an enclosure (probably plastic). Not that it matters, but in case anyone is interested, I'll be using a PIC16F876A w/ one of those nifty Allegro current sensors (so cool BTW) and a 3 digit 7seg. LED scrapped from a PC case. > > Anyway, I remember there was a discussion recently about transformerless power supplies on the piclist. I have found several similar schematics on the net for this scheme. > > Here's my question, is there any way to make it work without the Zener diode? Not that it's hard, but I'm trying to make this thing using stuff I already have, and I don't have any Zener diodes (damn Canadian RadioShack is going to the dogs). I know they're probably like $0.15 at digikey, but then there's the min. order fee $5.00 and then shipping $8.00 so a handfull of zeners would cost me almost $15.00. I really don't have enough money right now to order more stuff to make it worthwhile. > > So is there any other way of doing this, like maybe a resistor divider or some such thing, fed into a regulator? I really don't need much current, just enough for the pic to wake up, take a sample and go back to bed (and then the LEDs), maybe less than 100mA?. Do any of you gurus know any good tricks on the cheap that'll do this? Or should I just hack up a Wall Wart and use that transformer (might fight into the outlet box)? > > Another quickie, can I use a little 600:600 audio transformer from a telephone to provide some isolation with the "transformerless" power supply? > > In the meantime, I'll be routing through some scrap circuit boards from telephones and VCRs to see if I can find a suitable Zener diode. > > Thanks ahead of time. > > MJ Brush > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu