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MOSFET H Bridge

I have built the H bridge circuit at http://www.cadvision.com/blanchas/hexfet/np-s.htm
but cannot get it to work. There is never any voltage across the
bridge.

I built the top left portion of the circuit on breadboard, and found
that this was incapable of switching the motor on. With no load, when
switched on the drain of the MOSFET was at full supply voltage, but
when the motor is attached, it drops away completely as though the
MOFET has switched it's self off.

I am using IRF9530 AND IRF530 instead of IRF9Z30 and IRFZ40. Might
this be the source of the problems?
 
J

Joerg

Jan 1, 1970
0
John said:
Don't try to PWM this one. The shoot-through losses are going to be
horrific.

10K, around 1000pf and no T-on/T-off handling? Hoo boy, I can already
here a loud bang.
 
10K, around 1000pf and no T-on/T-off handling? Hoo boy, I can already
here a loud bang.

Ok, I've done some more testing and found a couple of problems. Most
were just wiring, and I've fixed them. But now the whole thing just
shorts out. I've found the problem is the lower N channel MOSFETS.
They are always conducting. When C or D is high, There is 12V between
the drain and +ve rail. But when C or D is low, there is still 12V.
I.e. the MOSFET for some reason is not turning off. I'm having the
same problem with PCB and breadboard versions. Any ideas as to what
could be wrong?

BTW I'm not planning to use it form PWM; just forward and reverse.
 
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