I can't figure this one out at all. Either something switches fast and noisy, slow and quiet (and hot) or it employs some kind of filtering. The only explanation I can think of for reverse phase dimming is it could function with a large parallel capacitor to soften the switch-off losslessly and I suppose capacitors are cheaper than chokes. A triac requires a series choke to soften it's switch-on current spike. Since the voltage across the triac will collapse rapidly and may ring a substantial RC snubber (not just a capacitor) will be needed in parallel with the triac. Also I notice a number of mains filters are capacitor-ended rather than choke-ended which is completely wrong for a triac, and I suppose that in the worst instance with a filter between line in and neutral then RFI would be dumped into the lamp leads leading to a common mode current that would be very hard to filter. I was asked to advise on a low noise heater control system for a specialist application. After prolonged discussions on the unfeasibility of phase angle we decided on a variable output DC supply as the power controller, with either the current or voltage being controlled by the PID temperature controller. Expensive option though. Oliver. ----- Original Message ----- From: "Michael Reid" To: Sent: 26 April 2003 04:58 Subject: Re: [EE]: Reverse Phase Dimming > I work for a manufacturer of home lighting control systems and the TRIAC vs. > reverse phase dimming (or lagging edge dimming) has heated up in the past > few years. CE approvals in Europe and other parts of the world test for > emmitted emissions and conducted emissions. TRIAC dimmers need massive > amounts of filtering to pass CE. Some of my clients claim that TRIAC > dimming is against code in some countries due to the high EMI output as they > turn on part way through the cycle. My previous company, Vantage Lighting > has a reverse phase dimmer that uses MOSFETS. It is expensive and limited > to 6 amps per channel, and is very easily blown. Of course they use 2 > MOSFETs per dimmer. There are a number of commercial IBGT dimmers on the > market. We've done some testing of IGBT's for dimming and they do run a > little hotter than TRIAC's and cost more. > > Here is some info from a document I found on my computer. I think it is > from an engineer in New Zealand by the name of Mike Pearce. He has a PIC > design for a dimmer with code for both types of dimming. If anyone wants > the files I can send them to you. > > > > An IGBT driver turns the output ON at the zero cross point and turns > > the output OFF part way through the cycle - this has really low > > EMI properties and is one of the few methods allowed for phase control > > in European countrys (i.e complies with EN55015 EMI standard). > > Other countries are following suit for example New Zealand and Austrailia > > are almost there (See AS/NZS 4051 and CISPR15 EMI Standards ) > > This method of dimming is audibly quiet, does not require extra filter > > componets (If designed properly).It also has a better lamp life and can > > control a wider range of lamps than the TRIAC method of dimming. > > > > > > > > > > Reverse Phase Dimming or Reverse Phase control, does anyone has some > references? > I would use it for light control. I would be glad to see IGBT in such > circuit. > Thanks > > -- > 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 > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu