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Topic: PWM H-Bridge circuit (Read 29 times) previous topic - next topic

will_eng

I have attached an H-Bridge circuit. I chose those Mosfets because I have them on hand. Does anyone see issues in using them together? They are both 12A,100V but one specifically says Logic Level optimized for 5V Gate drive. If this is an issue what would be good to use for a 12V and I guessing 9A power window motor form a car. I have been trying to do my homework on learning about motor drivers but I am still unsure. Should I be using a transistor or something between the inputs and arduino pins or is it that easy? I dont want to go and buy a $100 motor controller because of cost and the learning curve.


RuggedCircuits

You're OK on the N-channel MOSFET's but the P-channel MOSFET's need 12V on the gate to turn them off, and your Arduino will only output 5V.

I recommend an H-bridge driver chip like the TC4428 to act as an interface between the Arduino and the MOSFET bridge.

Also, using 12A MOSFET's for a 9A motor means the MOSFET's are probably going to get pretty hot (the "12A" number is the one the manufacturer specifies as an absolute worst-case cook-your-eggs-on-it type of number).

will_eng

Are there any good resources for sizing Mosfets to H-Bridge circuits?

will_eng

How is this? I'm still not exactly sure how to size the fets. I got these form someone using a similar motor (around 10A). But they are rated for 8 and 6.8A. My motor isn't marked but I found documentation that leads me to believe that it is 2.8A no load, < or = 9A, and 28A stall. The app will not require heavy loading and will probably never run at full load or speed. Also have I used the driver properly?


RuggedCircuits

Without heatsinking, my general rule of thumb is to keep power dissipation of TO-220 packages to 1W or less. Find the Rds(on) (i.e., on-resistance) value for your MOSFET's, then compute their power dissipation as P=I*I*R where I is the maximum current they will carry. For example, your RFP12N10L has an on-resistance of 0.2 ohms (pretty high for a MOSFET, actually), so at 9A it will dissipate 81*0.2=16.2W of heat. That is not good. I have some MOSFET recommendations here. The NDP6060L, for example, has an on-resistance of 0.025 ohms so will dissipate 81*0.025=2W which is much more manageable, and should be OK if you add a heat sink.

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