Old 10-18-2013, 12:31 AM #17
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Default Re: Burning Mosfets, could use advice.

The series resistor value isn't critical and can be anywhere between 10Ω and 100Ω. The 10k
resistor can be completely left out if your CNC board has a totem pole output which it loks
like it does. I suspect that there are inductive spikes coming back from the motors and
blowing your MOSFETs. The band on the zener diode goes toward the gate of the MOSFET.

Quote:
Originally Posted by Marksolberg View Post
The interweb tells me that the difference is that a zener diode can conduct current in a
reverse direction if the voltage difference is high enough. I'm not sure how that comes into
play here.
Any diode can conduct in the reverse direction, but zener diodes are designed for it. The
reverse voltage drop across a zener is less noisy and varies less from part to part. In this
circuit, we are using this property to "clamp" any input above a certain voltage and keep it
out of the gate of the MOSFET. Zener diodes will also conduct in the forward direction just
like any other diode. So in this case if there is any negative voltage coming from the CNC
board, this will also be clamped to whatever the forward voltage drop of the zener would be.
(Much less than the reverse voltage drop (zener voltage))

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Burning Mosfets, could use advice.-cnc-ld-driver.png  


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Old 10-18-2013, 04:34 AM #18
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Default Re: Burning Mosfets, could use advice.

Quote:
Originally Posted by Cyparagon View Post
I think Things meant to say don't make the value too high.
Indeed, that's what happens when you give advice at 1am
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Old 10-18-2013, 04:45 AM #19
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Default Re: Burning Mosfets, could use advice.

Quote:
Originally Posted by Things View Post
Indeed, that's what happens when you give advice at 1am
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