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As I was learning about MOSFETS today, I noticed that nearly every circuit diagram with a MOSFET features a large pulldown resistor placed in parallel to the transistor.

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For example, in this picture we can observe that a extremely large, 1 Mega Ohm resistor is placed parallel to our mosfet. While I understand that this resistor exists to primarily ground out any floating charges on the wire, I don't quite understand why the resistor is usually so large. Why doesn't a small pulldown resistor satisfy the issue of grounding floating values?

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    \$\begingroup\$ Did you consider the power loss if a signal applies a voltage? BTW, 1MOhm is not extremely large, tens or hundreds of MOhm are. ;-) \$\endgroup\$
    – the busybee
    Commented Jun 10, 2021 at 5:58
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    \$\begingroup\$ R1 helps dampen oscillation if the input is a low-impedance driver and R2 provides a galvanic connection to ground so that, if otherwise left alone, the gate leaks stored charge and will eventually find itself grounded in a managed way. \$\endgroup\$
    – jonk
    Commented Jun 10, 2021 at 6:03
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    \$\begingroup\$ Linking this post, helps clear up why the resistor used isn't even higher: electronics.stackexchange.com/questions/508330/… \$\endgroup\$
    – Dude156
    Commented Jun 10, 2021 at 6:09

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The ideia is to do not consume so much current from the source. For example, if you're using an 5V microcontroller, given an 1k resistor, each pin would consume 5 mA when in HIGH state. Now imagine 10 or 20 pins at same time, your micro would be driving 50 - 100 mA.

In many cases it's a 10k resistor.

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  • \$\begingroup\$ Thanks bruh, I've been trying to understand this for days, and that simple statement helped a bunch. \$\endgroup\$
    – Dude156
    Commented Jun 10, 2021 at 6:09

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