In a H-bridge with an inductor between the legs they conduct, yes. Let's say the upper left and the lower right switch is ON. On the inductor you have + on the left and - on the right. Turn off the switches , the inductor generates an inverted voltage that can be higher than the DC bus. Now all switches are off but since you'd have a (big) positive voltage on the right of the inductor and negative on the left the lower left mosfet diode and upper right mosfet diode will conduct. They will be forward biased.When an inductor is switched off, current will continue to try and flow towards the drain and the back biased cathode of the body diode. How is back emf being suppressed? You cannot push current back through the diode's cathode.
I don't think it's an H-bridge; it's four individual MOSFETs, each on a separate microcontroller output, and each controlling a separate winding of the stepper. I would post a schematic, but I don't have one since I sort of based the design on previous projects I have done.I forgot the H bridge part. I should of realized that when he said 4 MOSFET's. Kinda obvious.
Well in this case I think, yes, you should add diodes on the windings, since the mosfet body diode will never conduct. (I assume something like positive voltage --> motor winding --> drain of an N-FET --> source goes to GND) diode on the motor winding pointing to positive.I don't think it's an H-bridge; it's four individual MOSFETs, each on a separate microcontroller output, and each controlling a separate winding of the stepper. I would post a schematic, but I don't have one since I sort of based the design on previous projects I have done.
I apologize for the confusion.
I assume the MOSFETs are turning on fast enough, although I do have to put a 1 msec pause after each high command from the PICAXE. The MOSFETs do not get hot at all.If the MOSFETs aren't turning on fast enough and warming up, you could lower the 4 gate resistors to around 33 ohms or so, that will help. But if its working fine the way it is, I wouldn't bother.
What would be better than the 1N4001 diodes? Zeners? What voltage? Same polarity?The diodes are where they should be.
DipTrace. Thanks.What pgm did you use to generate the schematic?
IN4007,I already said that on my first post anyway that gives you :What would be better than the 1N4001 diodes? Zeners? What voltage? Same polarity?
You won't need higher voltage diodes. They are either reverse biased , when the mosfet is conducting (reverse voltage is DC-bus voltage) or forward biased right after the mosfet opened.What would be better than the 1N4001 diodes?
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