Preventing back EMF, which method?

[bbromhall]

Hi,

I am seeking some advice on preventing back EMF within a motor.

It is a 10A, 12v motor powered off a PWM power supply. It's 20kHz, with power MOSFETs.

What would be the best way to prevent back EMF into the circuit out of the following?

1. Flywheel diode and resistor
2. Filter circuit (?)
3. Flywheel MOSFET and capacitor

Quick feedback would be greatly appreciated,

Cheer!

Barney

 

[LiteYear]

Maybe I'm missing something, but why would you want to prevent back EMF? Perhaps if you describe the problem you're trying to solve or the goal your trying to achieve it might make more sense. Back EMF is a necessary and inherent phenomena in electric motors. The electrical circuit has very little to do with it - it's the magnetic properties of the motor that are most relevant.

Given you mention flywheel (do you mean free-wheeling?) diodes and filters, might you instead be concerned about switching losses or eddy current losses or something?

 

[Brad1979]

I've seen a lot of misinformation on hobby forums about protecting your control from back-emf. As LiteYear said, back-emf is an inherent phenomena in electric motors. What you are really looking for is protection against reverse voltage spikes due to the voltage being removed from the motor (inductive load). I've used a freewheeling diode before for this but I'll let somebody else answer your question, since I don't know what the best method is.

 

[imcjoek]

This reference does a very thorough job of explaining the gritty details of your typical MOSFET fullbridge. The bit I think you are interested in is the discussion on regenerative vs dynamic braking and essentially "what to do when the motor is acting as a generator?" And the answer to that is unfortunately not very easy.

http://modularcircuits.tantosonline.com/blog/articles/h-bridge-secrets/