>> I've been thinking of doing something like that, but with 2 mosfets 
>> or
>> IGBT's inverted back to back (like 2 SCR's to do full wave AC triac
>> control), ...

A single MOSFET will already conduct in both directions when turned 
on. ie for an N channel FET the gate must be positive relative to 
source BUT the drain can swing positive or negative, BUT ...

> Beware the body diode! You might end up with essentially a dead 
> short.

Indeed. The single FET will not be off in the reverse direction due to 
the body diode conducting. If you want to use FETs you can still use 
two, but you connect them in SERIES. The arrangement is very 
unintuitive. Connect source to soource and gate to gate (!) and 
connect AC path to be switched to the 2 drains. To turn on provide an 
appropriate positive voltage to the interconnected gates relative to 
the interconnected sources. This usually requires a floating supply - 
which can be annoying. A 9v PP3 (transistor radio size) alkaline 
battery should last 100 on hours here if switched at high frequency or 
approaching shelf life if switched occasionally and slow turn off/on 
is OK.

> It's usually simpler to wrap a single MOSFET/IGBT with a bridge 
> rectifier,
> as Roland showed, if you can tolerate the two additional diode 
> drops.

Probably true. Again, the gates float, but you can use a high 
resistance high voltage feed. As you could in the arrangement above. 
If doing this care needs to be taken to clamp gates so they don't 
exceed Vgsmax.



        RM

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist