How to Use a Zener Diode to Reduce DC Voltage

Zener diodes reduce and regulate DC voltages.
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Diodes are electronic parts that conduct current in only one direction. If you apply too much voltage in reverse, however, it forces the diode to conduct, destroying it. A Zener diode’s design has the special property of reducing a reverse voltage to a specified value. This makes Zener diodes good, low-cost voltage regulators. To use one in a circuit, you calculate a resistor value, then connect the resistor and Zener across the voltage you want to regulate. You connect the Zener backwards compared to standard diodes, since you want it to regulate, not conduct.

    Calculate the resistor’s resistance value by dividing the regulated voltage by the maximum current you want to flow through this part of the circuit. For example, if the voltage is 10 volts and the current is 0.01 amps, 10 / 0.01 = 1,000 ohms. Calculate its minimum wattage by squaring the current, multiply by the resistance, then double the result for safety.

    (.01)^2 x 1,000 x 2 = .2, so a 1/4 watt resistor (.25 watts) will work.

    Obtain the resistor and Zener diode from an electronics distributor.

    Cut four pieces of wire about 8 inches long. Strip about a half inch of wire from the ends of each.

    Insert the anode and cathode leads of the Zener diode into different columns on the solderless breadboard. Connect two of the wires to the Zener’s anode. Connect one of the resistor’s leads and one wire to the cathode. Insert the resistor’s remaining lead into an unused column on the board. Set the remaining wire so it shares this column.

    Connect the free end of the last wire to the positive terminal of the DC voltage source. Connect the free end of one of the Zener’s anode wires to the source’s negative terminal.

    Use the free anode and cathode wires to supply a circuit with regulated voltage. In this case, the cathode wire has a positive polarity and the anode will be negative.

    Things You'll Need

    • Calculator
    • Electronics distributor catalog
    • 22-gauge solid wire
    • Wire strippers
    • Zener diode
    • Resistor
    • Solderless breadboard
    • DC voltage source

    Tips

    • You can find Zener diodes with voltage ratings ranging from 2.4 to about 200 volts.

    Warnings

    • Do not exceed the Zener’s current rating, as this will damage it.

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