How to Make a 12 Volt DC Power Supply

Written by jerry walch Google
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Building DC (direct current) power supplies is a great way to discover the joy of building your own electronics. This 12-volt regulated power supply provides steady, well-regulated, pure DC for any small load requiring 12 volts to operate.

This is an easy project even for a beginner. There's nothing critical in the way you arrange the parts on the perfboard but an orderly layout of the parts will make for a neat wiring job.

Skill level:

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Things you need

  • 2-3/4-inch-by-6-inch prepunched IC-spacing perfboard
  • 3-3/4-inch-by-10-inch-by-1/2-inch plywood
  • Four 3/8-inch-by-1-inch tubular standoffs
  • Four #8-by-5/8-inch wood screws
  • Two #8-by-3/8-inch wood screws
  • Full-wave bridge rectifiers for power supplies
  • +12V fixed-voltage regulator 7812
  • 1000µF 35V 20% radial-lead electrolytic capacitor
  • 25.2V CT 2.0A heavy-duty chassis-mount transformer with lead
  • SPST lighted rocker switch
  • Power cord set
  • Four #8 flat washers
  • AWG 20, stranded copper hookup wire, red
  • AWG 20, stranded copper hookup wire, rlack
  • AWG 20 solid tinned copper buss wire
  • Soldering station or 35-watt soldering iron
  • Soldering sponge
  • Diagonal pliers/wire cutters
  • Wire strippers
  • Needle-nose pliers
  • Screwdrivers
  • Hammer
  • Insulated bell wire staples
  • Heat shrink tubing
  • Hot air gun

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  1. 1

    Position the perfboard toward one end of the plywood base, leaving 1/2 inch of plywood showing along the sides and end. Using a pencil or fine-point marker, mark the corner hole on the plywood base. You will attach the perfboard to the base using these holes.

  2. 2

    Mount the power transformer at the opposite end of the base, using the two #8-by-3/8-inch wood screws, with the two black primary winding leads facing the end edge.

  3. 3

    Turn on the soldering station or plug in the soldering iron and allow it to heat up. When it's hot, clean the soldering iron tip by wiping it on the wet soldering sponge.

  4. 4

    "Tin" the soldering iron tip by applying a fresh coating of rosin core solder. A properly tinned iron will appear bright and silvery.

  5. 5

    Mount the full-wave bridge rectifier toward one corner of the perfboard by inserting its four leads through holes in the board. Position it about 3/4 inches in from the side and 1 inch in from the end of the circuit board. Secure the bridge to the board by soldering each lead to the copper eyelet on the opposite side of the board.

  6. 6

    Once soldered in place, trim the leads so that they project 1/4 inches above the solder eyelet.

  7. 7

    Make 90-degree bends in the leads on the axial-lead electrolytic capacitor and pass them through two holes on the perfboard. Position the capacitor so that it's opposite the rectifier bridge on the board. Secure it in place by soldering its leads to the eyelets just as you did with the bridge.

  8. 8

    Mount the three terminal voltage regulator centred, an inch or two in front of the rectifier bridge and capacitor.

  9. 9

    Using a fine-point permanent marker, mark the terminals of the rectifier bridge on the solder side of the board. The two centre connections are the AC terminals and may be marked with "AC" or with a sine wave symbol (~). the outer two connections are the positive and negative DC output terminals and marked with a (+) and a (-) sign on the front of the bridge.

  10. 10

    Using the fine-point marker, mark the three terminals on the solder side of the board for the three-terminal voltage regulator IC (Integrated Circuit.) The terminals are numbered 1, 2 and 3, with 1 being the DC input terminal, 2 being the ground terminal and 3 being the DC output terminal.

  11. 11

    Cut two 24-inch-long pieces of hookup wire for the output leads, one black piece and one red piece, stripping 1/2 inches of insulation from their ends.

  12. 12

    Using the tinned buss wire, create a circuit trace between the negative lead of the capacitor and the negative bridge terminal.

  13. 13

    Repeat Step 12 for the positive side of the circuit.

  14. 14

    Using a short piece of red hookup wire, connect the #1 terminal on the voltage regulator to the positive buss wire.

  15. 15

    Using a short piece of black hookup wire, connect the #2 terminal to the negative buss.

  16. 16

    Connect the red output lead to the #3 output terminal of the regulator and the black output lead to the negative buss.

  17. 17

    Solder the two yellow secondary leads coming from the transformer to the AC terminal on the bridge.

  18. 18

    Mount the circuit board on the wood base using the four #8-by-5/8-inch wood screws and the four 3/8-inch-by-1-inch tubular standoffs.

  19. 19

    Solder the two black transformer primary leads to the cord set leads. Insulate the joints using the heat shrink tubing.

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