What Diode for DC Motor?

I've been building circuits since 2007 so I know I shouldn't 'have' to ask this question but I don't know the answer so I have to ask the forum.
What diode should I use for a DC motor @12volts and @20Khz PWM? On some projects I mix DC motors and servos at different voltages. Add to that a wireless module at yet another voltage.
I bought some optocouplers to isolate my Propellers until I figure out what I'm doing wrong. I have been experimenting with six to nine volts to power my motors but I want to scale up some of my projects to 12 or 24 volts.
Can I solve the problem with better diodes?


  • So what is going wrong? The Prop resets itself?
    Does it look like motors create ground bounce that raises the ground floor to high that it create a BOR?

    Tree Power (with inductors and caps) and Star Ground is design goal.

  • The problem goes back a few months. I posted a question because I couldn't figure out why I wasn't able to get a clean square wave at 20Khz. I had just bought a cheap oscilloscope that let me see the PWM. I remember Tracy Allen asking me to test different i/o pins. I suspected that he was onto something so I swapped out the Prop and the problem disappeared. Someone thought I could have destroyed the PLL.
    I had used that Propeller to drive two 9 volt DC motors, four 5 volt servos and an RF module @ 5 volts. I cannibalized that board so I can't give a lot of details about it...but I have been afraid to connect any motors to my Propellers since that time.
    I want to be able to wirelessly control a machine that has DC motors 'and' servos that I can scale up in size and power. My thought is that if I had the proper knowledge I would not 'have' to use opto's. Even though I'm not an engineer I should know this stuff after twelve years of building circuits.
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