Quote:
Originally Posted by rsisk
Question: why was a 100K ohm resistor used on the gate?
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Credit for the following answer goes to Eric VanWyk:
The purpose of the 100K resistor is to dampen electrical oscillations. The gate of the FET has some capacitance. The wiring leading to the gate pin may have some inductance. Under certain circumstances, together these may form an LC oscillator. The resistance is there to prevent those oscillations. The 100K is not critical. It can probably range over an entire order of magnitude. The higher the resistance, the better the damping, but the slower the FET's response to a step input signal (because of the gate capacitance). The lower the resistance, the faster the FET responds to a step input signal, but you increase the chances of oscillations.