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I tried to control the brightness of a LED using a Linear Hall Effect Sensor fed to an Arduino, and PWM output to the gate of a MOSFET connected to a 12V battery.

The LED was flickering a lot, and after some searching around, I found out that adding a 10k resistor to ground before the gate of my MOSFET solved the problem. However, I havent found a good explanation as to why this fixes the problem. Does anyone have an explanetion?

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  • \$\begingroup\$ maybe here "Ringing Reduction Techniques for High Performance MOSFETs" ti.com/lit/an/slpa010/slpa010.pdf \$\endgroup\$ – Roland Mieslinger Feb 10 '15 at 12:47
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    \$\begingroup\$ Was it a breadboard with flaky ground connections and power current to the load sharing the same 0V rail as the Arduino? \$\endgroup\$ – Andy aka Feb 10 '15 at 13:49
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As Roland Mieslinger posted on the gate you got some internal capacitor. This capacitor is loaded when you try to switch MOSFET ON. When you try to switch it OFF the load is still present on capacitor, making your transistor ON till the cap is unloaded. This resistor between the gate and GND is to unload a cap.

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It is possible that as the Mosfet switches on and off it is feeding noise back into the driver circuit. Since you did not describe the type of driver you are using does it have a proper drive voltage and current to operate the Mosfet. I have a Motor switching Mosfet and I have to have a ground plain below my circuit board to keep noise generate while switching from interfering with my drivers and timing circuits.

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I don't have any idea of what your code looks like, but I'm guessing that it is switching the port pin between input and output. That would explain what you are seeing.

If that is in fact what is going on, I'd reduce the resistor between Gate and Ground down to about 1k. That will cause the FET to turn OFF faster and reduce its dissipation.

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  • \$\begingroup\$ Or fix the code so that it actually drives the pin high and low. \$\endgroup\$ – Matt Young Mar 13 '15 at 15:07

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