And yet, NOBODY has attempted to answer his question(s), which he has 
now clarified a bit more.  Dwayne Reid "got it", in that this is 
intended as an ALTERNATIVE to "Phase control".  So stop talking about 
phase control, triacs, SMPS's, etc.... 

So please read Harold's original post, his current post (below), maybe a 
few of Dwayne's posts; and then reply if you have something of substance 
to offer.

BTW, setting it up with a single IGBT/FET with a diode bridge is 
probably easier/better, as you don't have to worry what state (on/off) 
your IGBT/FET is in during ZC.  I don't "think" you could have a pair of 
IGBT/FETS in series setup, and have both of them turned on at the same 
time without some problems cropping up.  Also, the problem with "reverse 
phase control" (#1 method below) is that you can't use it on an 
inductive load, where as in the #2 method it doesn't matter.  As to 
driving the gate(s), that's where I got stumped too....



Harold Hallikainen wrote:

>OK, since I started the thread long ago and watched it drift off someplace
>far away, I'll make a few comments.
>
>We're currently manufacturing triac and SCR (solid state relay) based
>light dimmers. They use phase control and have chokes to limit rise time.
>I'm looking at alternatives.
>
>#1 is to use FET or IGBT switching and still use phase control or "reverse
>phase control" (where we turn the lamp off part way through the AC cycle
>intead of turning it on part way through the AC cycle) and varying the
>risetime by slowly turning on the FET (resulting in less efficiency, but
>we're also dissipating some power in our chokes).
>
>#2 is to use FET or IGBT switching to chop the AC waveform at a high
>frequency, then filter out the high frequency. We end up with a sine wave
>whose RMS voltage is the incoming RMS voltage times the duty cycle of the
>chop voltage.
>
>BOTH of these require the use of one or two IGBTs or FETs to switch the
>AC. How are people doing this? Are you using one IGBT or FET and a diode
>bridge, or a pair of devices in series with steering diodes around the
>"backward" device?
>
>Second, how are the gates being driven? If you use a typical FET driver,
>you need a floating power supply for each switched line, which is pretty
>complicated. How about pulse transformers to drive the gates? Do you put
>clamp circuits to restore the DC component of the drive?
>
>I haven't seen any application notes that describe this.
>
>THANKS!
>
>Harold
>
>
>  
>


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