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Novice to control a motor speed...


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Hi !

Examining circuits to control a DC motor I am planning to use to build an electric car, I notice a diode in parallel to the armature. I see it will absorb back EMF produced by the motor and protect the power drivers by shorting the reverse current path.


Why is not preferred to install the diode in parallel to the power driver transistor o Mosfet instead?


I believe a diode in this second form of application would send the EMF back to the battery instead of wasting it as heat.


Any web site link where to learn about using aircraft generators as motors for electric vehicle would be appreciated.




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  • 2 weeks later...

Hello Externet


Either method can be used.

If the impedance of the supply is very low, then you can use the supply to absorb the energy from the armature, however rembmer to take into acount the High frequency impedance because the MOS FETs switch very quickly. The inductance of the supply can cause very high and fast transients to be presented to the MOS FETs. You will probably need to use good snubber networkds and over voltage protection around the MOS FETs.


Both methods can be used, but the flyback diode across the armature is the safest method.

Best regards,

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