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Connecting signal GND to power GND

steelgoofy

Oct 15, 2014
6
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Oct 15, 2014
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Hy!

I' ve built a circuit to drive a 3 phase BLDC, using a micro controller and gate driver IC (schematic included). I' ve already tested it once, but it turned out that one of my Mosfet was wrong and it created a short between 12 V to GND and it dameged my micro controller. I've replaced the Mosfet, but before I test it I want to be sure that I'm not going to make any mistakes. So when I apply 5V and above to the gates and switching the Mosfets to commutate the BLDC I create a short (incidental), as the coils have very low (0,3 Ohm) resistance. I also have to connect the uC's and the driver's ground, and the driver IC GND to the power supply GND, because it needs to be supplied with 12 V. So the result is that my uC GND is connected to the power supply GND, which I think can damage my uC again, when the motor works. Adding another power supply for driver ic might be good, but I really dont want to use another supply. Could you help me to solve this, or do you think it is safe ?
 

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Arouse1973

Adam
Dec 18, 2013
5,178
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Dec 18, 2013
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Not quite sure how it damaged your micro but you need the common point for the circuit to work. Is this a driver module you are using like the DRV8302? Or are you doing your own? You need to make sure the PWM coming out of the driver has the correct timings for the MOSFETS. If this is an off the shelf module then as along as you follow the application note for input PWM it should take care of the rest. Double check your MOSFET connections and try again. If you are really nervous then fit a fuse (Slow blow type) of the correct value on the supply to the MOSFETS. It would also be a good idea to have a current monitoring circuit in case two of the MOSFET pairs switched on at the same time.
Adam
 
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