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: Hello Bert! Hey it's been awhile since I've written and I hope you've been
: well. I've got a new job installing high voltage high current sensors for
: utility companies using fiber optics to sense the magnetic field. Cool
: stuff. Anyways, What I'd like your advice on is I have a very crude ac/dc
: supply powering a string of led's. For instance, if the input is 120ac I
: have it going through a full wave rectifier and can power about 40 leds at
: about 28ma. My question is if I just use the rectifier and a 10-20uf cap
: to smooth out the dc, will it pass UL testing? I will have a UL rated 600v
: cable going into a small metal box with the hot going through a 500ma
: fuse. The box will be tied to earth ground and the hot and neutral will go
: to the input of the rectifier on a small circuit board and the unregulated
: output will of course go to my string of led's. Do I need to add a tank
: circuit or an emi filter? What about RFI? The led board will be mounted to
: a UHMW 1/4" mounting plate. Your help is of course greatly
: Hi Jerry,
: With this simple circuit you won't have to worry about RFI or emissions
: filtering since nothing in your system will be creating any high frequency
: nastiness. However, since the LED's are directly connected to the incoming
: mains, there will be some safety consideratinos that need to be addressed.
: These would include the possibility of a person accidentally making
: contact with the mains, or fire hazard under abnormal
: operation/conditions. You can avoid some of these concerns by powering the
: LED's from a Class 2 current limited low voltage transformer and DC power
: supply - a "wall wart" - instead of directly off the line.
: Adding an electrolytic capacitor to filter the DC will reduce LED
: flickering a bit, but otherwise may not be necessary.
: If you intend to offer this as a commercial product, you may wish to
: contact an expert in UL/CSA requirements/verification.
: Good luck,
Thank you very much for the info. The mains that you're speaking of I'm assuming are the 120-277vac from facility input feed? or the high voltage DC that'll be coming out of the supply? If it's the AC input, then the same safety considerations would be the same for the 208-277vac for the metal halide light fixtures as well wouldn't it? I'm just curious if the concern is because of the high DC potential.
My power supply layout includes a varistor across the AC input, C1(47uf/350v) and R1 (200k) have a time constant (calc) of about 10 seconds and I measured 200v@5sec, 108v@10sec, 61v@15sec, 33v@20, 19v@25sec and at 30seconds the supply is under 10vdc. C2 is a 68pf. There is also a fuseable trace that's 35um thk x 4 mil wide and Imax. is .357a. and the supply board is potted in the box. Can you think of anything else?
By the way anything new going on at your end?