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

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Edson Brusque                 C.I.Tronics Lighting Designers Ltda
Researcher and Developer               Blumenau  -  SC  -  Brazil
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