Re: PCB design: driver circuit

If you don't just need on/off, a bridge switching circuit can
approximate as much of a sinewave as you wish with the help of a PWM
signal. You connect two MOSFETs (or bipolars) so you can switch each
motor lead to B+ or B-. Three-phase AC induction can be done with six
switches. Just remember to have a few microseconds of off time when
you alternate between switching the upper and lower switch on so you
don't short B+ to B-. The duty cycle between the upper and lower
switch determines the percentage of your B+ voltage you will have on
that motor lead. You can control servos using this technique, too.
The efficiency can be very high.

Good luck!
Don

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Trend" <fredit@c...> wrote:
> Alright, I am designing the card right now, but have a newbie
question.. How
> well do DC and AC interact?
> I have 25-35x AC motors, and need to control them via the
> parallel/serial/usb port, but I was planning on using some NPN
transistors
> as amps, with the base being DC and the amp power being the
collector..
> But for some reason I don't think this will work...
>
> Any ideas?
>
> thanks-lee
>