PWM motor controllers, Half bridge, no bridge, etc

Discussion in 'General Electronics Chat' started by HellTriX, Apr 18, 2008.

  1. HellTriX

    HellTriX Thread Starter Active Member

    Apr 11, 2008
    Vancouver, Washington
    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.

  2. SgtWookie

    SgtWookie Expert

    Jul 17, 2007
    In the vast midwest of the USA; CST
    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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