DIY Transistor Voltage Regulator

Written by j.t. barett
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DIY Transistor Voltage Regulator
A transistor allows this regulator to handle more current. (four gold transistors on blue image by Eugene Tokarev from Fotolia.com)

Most electronics projects benefit from having a voltage-regulated DC power supply. Making your own discrete transistor voltage regulator can serve as a relatively painless lesson in power supply design. While integrated regulators such as the 7805 are simple to use, their black-box approach reveals little about their inner workings. A design using a zener diode and pass transistor delivers decent regulation while giving you better insights as to how it works.

Skill level:
Moderate

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Things you need

  • 2N2222 transistor data sheet
  • 2N2222 transistor
  • Perfboard
  • 1.2K-ohm ½-watt resistor
  • 47K-ohm ½-watt resistor
  • 10-microfarad 30-volt electrolytic capacitor
  • 30-watt soldering iron
  • Electronics solder
  • 1N4104 10-volt zener diode
  • 22-gauge wire
  • Wire strippers
  • Masking tape
  • Pen
  • Unregulated DC power supply

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Instructions

  1. 1

    Read the 2N2222 transistor's data sheet. Note which of its leads are the base, collector and emitter.

  2. 2

    Insert the transistor into the perfboard so that each lead goes through its own hole. On the bottom side, spread the leads out at a slight angle to prevent the transistor from slipping out.

  3. 3

    Place the cathode lead of the zener diode through the perfboard near the transistor's base. Insert the anode lead through any nearby hole. Insert one lead of the 47K-ohm resistor near the zener's anode. Insert the other lead near the transistor's emitter. Place the positive lead of the 10-microfarad capacitor near the emitter and resistor lead. Place the capacitor's negative lead near the zener's anode.

  4. 4

    Cut four 12-inch lengths of 22-gauge wire. Remove ¼-inch of insulation from each end of the wires with the wire strippers.

  5. 5

    Place the end of one wire near the point where the capacitor positive lead meets the transistor emitter and resistor leads. Solder the wire, emitter, capacitor and resistor leads together and trim the excess with the diagonal cutters. With the masking tape and pen, label the wire "+Output."

  6. 6

    Insert one end of two wires through a hole near the zener's anode, the capacitor negative lead and resistor lead. Solder this connection and trim excess wire. Label both wires "Ground."

  7. 7

    Place one lead of the 1.2K-ohm resistor near the transistor's base lead. Solder the connection between this resistor, the zener diode's cathode and the base lead. Trim excess lead and wire.

  8. 8

    Insert the other resistor lead near the transistor's collector. Place one wire near the same point and solder the wire and two leads. Clip the excess material. Label this wire "+Input."

  9. 9

    Connect the wire labelled "+Input" to an unregulated DC source of positive voltage in the range of 15 to 22 volts. Connect one "Ground" wire to the unregulated DC source's ground. The regulator circuit you just made will hold the voltage between the "+Output" and remaining "Ground" to 10 volts.

Tips and warnings

  • Zener diodes are rated for different voltages. Select a different zener diode number if you want to regulate to a voltage other than 10 volts.
  • In this circuit, the zener does the actual voltage regulation. It controls the transistor, which lets the regulator circuit deliver more current than the zener could on its own.

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