MOSFET H Bridge

Jul 19, 2008 4 Replies
T

I have built the H bridge circuit at

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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?


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T

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As long as you're using N channels where N channels should be, P channels where P channels should be, you've got your sources and drains in the right places, and you're within the current ratings of the FETs, it should work.

Check your wiring.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html
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J

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Don't try to PWM this one. The shoot-through losses are going to be horrific.

John

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J

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10K, around 1000pf and no T-on/T-off handling? Hoo boy, I can already here a loud bang.
Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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T

at

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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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