Hey r/explainlikeimfive could someone explain to me how a pull down voltage circuit works? I tried googling it but I can’t make sense of the answers I’m getting.
Thank you in advance!
In: Technology
The super simple answer: A pull down (or a pull up) resistor is a way to set a “default” voltage on a pin/wire when nothing else in the circuit is trying to impose a voltage on it. A pull down resistor defaults the pin to the low/ground state.
An example: Lets say you have an output on a microchip that in the “on” looks like a 50-ohm resistor connected to 5V, and in the “off” state looks like a 50,000,000-ohm resistor connected to 5V.
Now what you really want is when the output is “on” that it has ~5V on it, and when it’s “off” it’s at ground. So what you do is put in a decent sized (say 50,000 ohm) resistor that connects that pin to ground (i.e. it’s a resistor that “pulls down” the voltage if the only inputs on a line are very high resistance). So in the on state you have:
5V – (50 ohm) – pin – (50,000 ohm) – ground.
Which means the pin will end up very close to 5V.
On the “off” state you will have:
5V – (50,000,000 ohm) – pin – (50,000 ohm) – ground
Which would mean the pin is very close to ground.
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