How does a pull down resistor work?

A pull-down resistor works in the same way but is connected to ground. It holds the logic signal near zero volts when no other active device is connected. The value of a pull down or pull up resistor will vary depending upon your specific devices involved.
A.

What is meant by pull down transistor?

Similarly for input high, NMOS is ON, PMOS is OFF. The output is shorted to ground via NMOS. Hence we say, "output is pulled down to ground", hence the name pull down transistor for NMOS. Its withrespect to the output voltage level that we use the phrases "pull up"/"pull down"
  • How does a pull up resistor work?

    Pull-ups are often used with buttons and switches. With a pull-up resistor, the input pin will read a high state when the button is not pressed. In other words, a small amount of current is flowing between VCC and the input pin (not to ground), thus the input pin reads close to VCC.
  • What is the VCC?

    Definition of: Vcc. Vcc. An electronics designation that refers to voltage from a power supply connected to the "collector" terminal of a bipolar transistor. In an NPN bipolar (BJT) transistor, it would be +Vcc, while in a PNP transistor, it would be -Vcc. Double letters (cc) refer to power supply voltages.
  • Why BJT is called a current controlled device?

    A MOSFET is known as a voltage controlled device because a voltage applied to the gate controls the flow of current between the source and drain. For a BJT the principal is the same. It is a current controlled device because the base current controls the current flow from the emitter to collector.
B.

What is the difference between a pull up and pull down?

Pull up is where you place a resistor between a signal and +V, pull down is pulling it to ground. Here, you can see that when the switch is open, in the pullup scenario the input pin will read high, but for pull down it will read low.
  • What value for pull up resistor?

    A rule of thumb is to use a resistor that is at least 10 times smaller than the value of the input pin impedance. In bipolar logic families which operate at operating at 5V, the typical pull-up resistor value is 1-5 kΩ. For switch and resistive sensor applications, the typical pull-up resistor value is 1-10 kΩ.
  • What is the VCC?

    Definition of: Vcc. Vcc. An electronics designation that refers to voltage from a power supply connected to the "collector" terminal of a bipolar transistor. In an NPN bipolar (BJT) transistor, it would be +Vcc, while in a PNP transistor, it would be -Vcc. Double letters (cc) refer to power supply voltages.
  • What is the voltage divider?

    A voltage divider is a simple circuit which turns a large voltage into a smaller one. Using just two series resistors and an input voltage, we can create an output voltage that is a fraction of the input. Voltage dividers are one of the most fundamental circuits in electronics.

Updated: 26th November 2019

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