Pull-down resistor

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A circuit showing a pull-up resistor (R2) and a pull-down resistor (R1)

Pull-down resistors are used in the design of electronic logic circuits to hold the input to a logic gate at a zero (low) value when no other component is driving the input. They are used less often than pull-up resistors.

Pull-down resistors can safely be used with CMOS logic gates because the inputs are voltage-controlled. TTL logic inputs that are left un-connected inherently float high, thus they require a much lower valued pull-down resistor to force the input low. This also consumes more current. For that reason, pull-up resistors are preferred in TTL circuits.

[edit] See also

• Pull-up resistor