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Sounds like your motor inductance is frying your MOSFET... Do you have a diode across your motor leads? Anode to MOSFET side & Cathode to + side. Thad --- nathanchronister <> wrote: > Hi. I'm using the BX24 to control a DC motor. I have > the PWM output > of the BX24 hooked up to an N-channel MOSFET. (I'm > not using an H- > bridge because I don't need reverse.) Even though > the MOSFET is rated > 25 amps and should easily handle the motor current > it keeps burning > out. After this happens the motor won't shut off. > > I have the BX24 wired *directly* to the Gate pin of > the MOSFET. The > Gate is also wired to the ground via a 1000 ohm > resistor. This is > intended to prevent static electricity from turning > the MOSFET on. > > The Source pin of the MOSFET is also wired to the > ground. > > The Drain pin is wired to the motor, and the other > motor lead goes to > the + side of the 7.4 volt battery which drives the > motor. > > The BX24 is powered by the developers board. The > motor control > circuit is grounded on the ground strip on the > developers board and > the - battery lead goes to the ground strip also. > > When this is all set up, it works fine for a while, > and then the > motor will switch full on and I have to unplug the > battery to make it > stop. (The PWM is correct however and the MOSFET > failed to work > correctly when tested separate from the BX24.) Does > it sound like I'm > doing something wrong which could cause the MOSFET > to fail? > > Thanks for your help! > Nathan __________________________________ |
MOSFET keeps burning out
Started by ●June 28, 2004
Reply by ●June 30, 20042004-06-30
Reply by ●June 30, 20042004-06-30
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Nathan, Quite a long time ago I used the app note referred to below for N channel MOSFET motor driver designs. Newer devices have improved characteristics, but the critical areas (like gate drive) still need to be fully understood to produce robust designs. Be willing to do a lot of testing, it will pay off in the long run. http://www.onsemi.com/pub/Collateral/AN1102-D.PDF Happy Switching, Eric ......> Paul, were you suggesting that a 100 ohm resistor between the BX and > the Gate would help it turn on all the way? Could you explain how > that works? > > The MOSFET is Fairchild Semi's #NDP603AL. I think it has all the > right specs but I'm new to this so I could be wrong. Here is the > documentation page: http://www.fairchildsemi.com/ds/ND/NDP603AL.pdf > > The internal diode is rated 25 amps but only 1.5 volts. Could that be > the problem? > > Nathan |
