Hey SparkyGuy,
I thought of making a variable AC supply twenty years ago. Never did, just
bought
a variac or three. The attached JPG was the direction I first that about.
I'm sure others will have suggestions for proper implementation.
Mike

amdx wrote:
I thought of making a variable AC supply twenty years ago. Never did, just
bought a variac or three. The attached JPG was the direction I first that about.
I'm sure others will have suggestions for proper implementation.

I am not really great at this kind of circuit but:
- MOSFET current is based on Vgs which means the gate has to be
referenced off the rectified AC rather than "ground." In a practical
circuit you might need an opto or something there.
- The FET limited current is pretty square, which doesn't couple well
into the transformer. Simulation shows the output to be very noisy
unless the FET is full on.

Maybe if you fed the gate with an attenuated copy of the AC input
(through a potentiometer, transformer and rectifier?).

Have I missed anything?