I want to understand the idea behind using a pull-up resistor.
While looking on the Internet, I came across the following description:
By using these two pull-up resistors, one for each input, when switch “A” or “B” is open (OFF), the input is effectively connected to the +5V supply rail via the pull-up resistor. The result is that as there is very little input current into the input of the logic gate, very little voltage is dropped across the pull-up resistor so nearly all the +5V supply voltage is applied to the input pin creating a HIGH, logic “1” condition.
Source: Electronics Tutorials - Pull-up Resistor Application
I assume the same logic is applied to all pull-up resistor applications.
- Why is there very little input current into the input of a logic gate?
- What guarantees that?
- How do I make sure there is only a small voltage drop on the resistor?