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- Mark Harriss
May 19, 2010, 12:27 pm
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I've been playing around with a prototype 15 Amp, 200 Volt PWM
power supply I built today trying to get it to work. It worked
fine with only one MOSFET at low loads with a DC motor connected.
Once three parallel MOSFETS were hooked up it would immediately
blow one MOSFET and not work with the motor but would work with
a 100 lightbulb dummy load. Then it would blow with the motor
despite having a suitable back EMF diode.
While scratching my head I noticed the FM radio was getting
interference which is pretty hard to do with FM. I had to be
getting some parasitic oscillations with strong harmonics up into
the 10's of MHz. Anyway three ferrite beads on each gate terminal
later and the whole thing worked fine with only slight faint
interference on the AM band that a small filter cap fixed.
I love it when things work the way they were intended!.