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Old 04-19-2008, 02:29 AM
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Default PWM motor controllers, Half bridge, no bridge, etc

So I have been experimenting with PWM and motor controllers and I now have some questions.

I understand an H-bridge is good for reversing an electric motor. But what is the main purpose of an half bridge? Is it to get forward motor voltage and freewheeling?

I ordered a driver chip but the wrong one came so I was unable to test out a half bridge using 2 N channel fets. So I hooked up a large DC fan from Vcc to the Drain of the mosfet and was able to get a variable motor controller up to about 23amps at 16v (I didn't run it and harder as my fuse is 25Amp).

I only had a single 3A diode in parallel with the motor to help protect the mosfet. I am assuming this is required for power mosfets?

So my next question is. What is wrong with just using a low side mosfet for running this motor? Do I need a high side to provide freewheeling, braking, or is that for protecting the low side mosfet?

The mosfets are 75v 75amp continuous rated and I have a few I'd like to parallel to test a 200 amp motor at 36-48v but I want to understand whats going on better so I don't destroy expensive mosfets.

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Old 04-19-2008, 03:16 AM
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Well, if it's just a single half-bridge, one big advantage is the ability to physically place it away from the other half-bridge so that you can use physically larger heat sinks.

If it's a full H-bridge IC, the power rating will be much smaller than a half bridge; there just is not sufficient area available to dissipate the heat.
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