On Tue, 19 Feb 2002, Vasile Surducan wrote:

> On Mon, 18 Feb 2002, Spehro Pefhany wrote:
>
> > >            0--------------------------0
> > >
> > >         FROM 12V                  TO LAMP
> > >         XFORMER                    STRING
> > >
> > >            0------+           +-------0
> > >                   |           |
> > >                   |           |
> > >                   |           |
> > >                   |           |
> > >                   D           D
> > >               Q1    G---+---G    Q2
> > >              Nch  S     |     S  Nch
> > >                   |     |     |
> > >  GATE DRV  0------------+     |
> > >                   |           |
> > >                   |           |
> > >  PIC GND   0------+-----------+
> > >
> > >Voila...
> >
> > Very nice, Dave! A couple of IRLZ544's maybe. They would have
> > a total drop of about 1.1V at 20A, so about as good as a triac.
> > At 10A, they'd beat it by a mile.
> >
>   eh, eh you have too rested minds guys !
>   This will never work, take a look better ...

Vasile,

Can you tell me why you think it won't work?  It looks to me like each
MOSFET's body diode will conduct "in reverse" during the half-cycle when
Vds < 0, and the opposing MOSFET will conduct if the gate is driven
high...  I do see one thing less than ideal, though, which appears to be a
loss of the Vf of the body diode.  For an IRLZ44 this looks like 2.5V max,
or around 1.7V for the 2SK2614.

Looks like at my 7A or so load this would work out to...  let me see...
1.7V * 7A = 11.9W dissiption, is that right?  But only for half the cycle,
figure roughly 2.7W or so for the other half cycle (P=I^2R where I=7A and
R=.055 typ.) meaning an average of about 7.3W per package for the 2SK2614,
9.4W for the IRLZ44.  That's 14+ to nearly 20W total...  Sure wouldn't
have to worry about condensation in the box!

The relay is looking better now, but I don't see where the dual-MOSFET
idea wouldn't work.  But of course IANAEE...  I may be all wet on part
or all of this, someone please tell me if I am.

Dale

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