At 09:03 AM 11/9/01 -0800, you wrote:

>        So, the question, it seems, is WHY would reverse phase control be
better
>than forward phase control? The only reason I can think of is varying
>lamp resistance through the cycle, but I wonder how much that actually
>varies.

On reflection, you pretty much have to be right on this. And "soft" turn on
is as possible as turn-off. You save the weight and cost of an inductor but
lose more efficiency. So, why not SCRs and a hefty series inductor?

The other possible advantage of using an IGBT is the possibility of detecting
a short or arc very quickly and shutting it down. Some are "short-circuit"
rated
for this kind of service, which is actually very hard on the IGBT, the
turn-off
can kill the IGBT if it isn't done just right. It's not possible at all with
thyristors, you have to depend on a fast and expensive I2T fuse to protect
the semiconductor.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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