I made a reverse dimmer in about 1987 using an irfp450 and a 555. The curcuit had bult in current limit so you could short the output and it just shut off until you removed it. Later I used it without the dimmer to limit the inrush current in lamps for traffic lights, to improve the life. I was a very simple curcuit, just semse the drop across the fet with a small bipolar transistor wich then shunted the gate to ground. ----- Original Message ----- From: "Edson Brusque" To: Sent: Sunday, February 24, 2002 3:06 PM Subject: Re: [EE]: Switching low-voltage AC > Hello Chris, Dave et all, > > Chris: > >I remember an ap note - perhaps from I.R. or Eupec on using IGBT's > >similarly. > >I will try to dig it up. This is really getting interesting... > > I've downloaded about 15 app notes today from I.R., but can't find this > information. Please, tell me when you've found it. > > Dave: > >What's reverse dimming? Is that where conduction begins on the zero > >crossing and then shuts off partway through the cycle? > > yes, you got it. > > >I've never used IGBTs and I only know a little about them. But from > >what I've read they should function in this circuit, provided you put a > >diode in parallel with each one so current can go around it during its > >"OFF" half of the cycle. > > I've tried with a pair of IRG4BC30UD (D is from Diode) and this worked, > but I haven't measured the voltage drop. > > >This circuit, using MOSFETs, would certainly not be very good for high > >voltage applications because of the relatively high Rds(on) of FETs with > >high breakdown voltages. Also, I would expect real problems--maybe > >insurmountable ones--with the huge current surges that occur during lamp > >burnout in high voltage circuits. > > Yes, bipolar transistors work ok for high voltage, MOSFETs are perfect > for large currents, if you want both you must use IGBTs. > > >Maybe IGBTs would alleviate these problems; I don't know. > > Yes, this is the idea. > > Best regards, > > Brusque > > ----------------------------------------------------------------- > Edson Brusque C.I.Tronics Lighting Designers Ltda > Researcher and Developer Blumenau - SC - Brazil > Say NO to HTML mail www.citronics.com.br > ----------------------------------------------------------------- > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body