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NPN Transistor AND Gate Circuit

  • Concept of Operation

    An electronic AND gate performs the digital logic AND function. The output is only high when both inputs are high. When either or both inputs are low, the output is low.

    The example transistor AND gate circuit is implemented here using PN2222A NPN transistors (a variant of the 2N2222A) but many common NPN bipolar junction transistors could be substituted.

    The gate is built from two transistor switch circuits wired in series. The inputs to the AND gate are two manual push button switches each of which drives a transistor. It should hopefully be reasonably apparent in the schematic below that when either switch is off, the voltage at the output is low, but when both switches are on, voltage at the output is high.

  • Schematic

  • Breadboard Diagram

  • Parts

    • PN2222A - NPN General Purpose Transistor (x2)
    • 10K Resistor (x2)
    • 1K Resistor (x1)
    • Green 5v LED (x1)
    • Tactile Pushbutton Switch (x2)

    (All parts for the project are available in our store.)

  • Truth Table

    In Out
    0 0 0
    0 1 0
    1 0 0
    1 1 1

  • PN2222A Pinout

  • Notes on Implementation

    1. The LEDs used in the project have a built in current limiting resistor eliminating the need for an external resistor to protect the device. This resistor is shown in the schematic as a resistor with the value “Lim” for completeness.
    2. The circuit was built and tested at 4.8 volts DC (4 AA NiMH rechargeable batteries).