simulate this circuit – Schematic created using CircuitLab

In above schematic;

  1. what value should R1 have? is it even needed?
  2. do we need that pull down resistor(R2)? if yes, 10K is enough or we need higher value like 100K resistor there?


1 Answer 1

  1. It's better with resistor so output driver isn't stressed to its maximum limits. Gate has its capacitance so it's better to limit charge/discharge current for such weak source

  2. As the gate is basically capacitor, it has really big input impedance. Without pull down resistor it'll be catching all kinds of EMI (electro-magnetic interferences). So 10k is fine. The 100k might be less unreliable if the mcu output is not active (boot/reset)

  • Thanks, but what value should R1 have? 220 ohm is enough? Jul 7, 2019 at 9:06
  • 2
    Ohm law. Output voltage is probably 5V and maximum current on avr pin is less than 30mA. So you shouldn't go under 166R. That 220R sounds fine. Bigger values could cause longer transitions between fully on and closed states and bigger losses. But it's the problem on much higher frequencies than the default analogWrite provides
    – KIIV
    Jul 7, 2019 at 9:15

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