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How to Use Triac in a Dimmer

A triac is a three-terminal electronic device that acts like a switch. When its gate lead receives a low-current triggering voltage, the other two terminals conduct. Unlike silicon-controlled rectifiers, also used to switch currents, the triac conducts in both directions. It operates faster than mechanical switches and does not wear out. In a dimmer circuit, the triac triggers on the AC (alternating-current) waveform. If it turns off early in the AC cycle, a connected lamp sees very little power. As it turns off progressively higher on the AC waveform̵7;s peak, the lamp becomes brighter.

Things You'll Need

  • 2 pieces of 22-gauge 8-inch stranded wire
  • Wire strippers
  • 50K-ohm variable resistor
  • Long-nose pliers
  • 15- to 30-watt soldering iron
  • Electronics solder
  • TMA34X triac (or equivalent)
  • Perfboard
  • .068-microfarad, 250-volt capacitor
  • 18-gauge lamp cord with two-prong appliance plug on one end, bare wires on the other
  • 18-gauge lamp cord with two-prong appliance socket on one end, bare wires on the other
  • Wire nut for 18-gauge wire
  • Electrical tape
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Instructions

    • 1

      Strip 1 inch of insulation from each end of the two 8-inch wires.

    • 2

      Slip the end of one piece of 8-inch wire into one of the end lugs of the 50K-ohm variable resistor. Crimp the wire onto the lug with the long-nose pliers. Slip one end of the second wire into the variable resistor̵7;s wiper lug and the remaining end lug. Solder the three connections.

    • 3

      Insert the leads of the triac into the perfboard. Feed one of the 8-inch wires through the perfboard near the triac̵7;s T2 lead. Crimp the wire to the T2 lead on the bottom side of the perfboard. Do not solder this connection yet. Feed the other 8-inch wire through the perfboard near the triac̵7;s gate lead. Crimp this wire to the gate lead, but do not solder.

    • 4

      Insert one lead of the capacitor near the triac̵7;s gate lead. Solder the capacitor lead and wire to the triac̵7;s gate lead on the bottom side of the board. Insert the capacitor̵7;s other lead near the triac̵7;s T1 lead. Crimp the connection, but do not solder.

    • 5

      Insert one wire from the lamp cord with two-prong plug near the triac̵7;s T1 lead. Crimp the wire to the T1 lead, and solder the connections.

    • 6

      Twist the remaining wire from the lamp cord with the two-prong plug together with a wire from the two-prong socket. Screw a wire nut on the twisted wire pair. Make sure that no loose wire strands protrude from the wire nut.

    • 7

      Insert the remaining wire from the cord with the two-prong plug through the board near triac̵7;s T2 lead. Crimp the wire, and solder the connections at the T2 lead.

    • 8

      Use pieces of electrical tape to cover and insulate the exposed lamp cord wiring on the bottom of the perfboard.

    • 9

      Plug an incandescent lamp of 60 watts or less into the lamp cord socket. Insert the plug into a household receptacle. Turn the shaft on the variable resistor; the lamp should brighten and dim.


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