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 waveform’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
Instructions
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1
Strip 1 inch of insulation from each end of the two 8-inch wires.
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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 resistor’s wiper lug and the remaining end lug. Solder the three connections.
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3
Insert the leads of the triac into the perfboard. Feed one of the 8-inch wires through the perfboard near the triac’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 triac’s gate lead. Crimp this wire to the gate lead, but do not solder.
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4
Insert one lead of the capacitor near the triac’s gate lead. Solder the capacitor lead and wire to the triac’s gate lead on the bottom side of the board. Insert the capacitor’s other lead near the triac’s T1 lead. Crimp the connection, but do not solder.
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5
Insert one wire from the lamp cord with two-prong plug near the triac’s T1 lead. Crimp the wire to the T1 lead, and solder the connections.
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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.
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7
Insert the remaining wire from the cord with the two-prong plug through the board near triac’s T2 lead. Crimp the wire, and solder the connections at the T2 lead.
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8
Use pieces of electrical tape to cover and insulate the exposed lamp cord wiring on the bottom of the perfboard.
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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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Tips & Warnings
Any exposed wiring will pose a mild shock hazard. Make sure exposed wiring has at least one layer of electrical tape.
Do not use this dimmer circuit with power tools or any electrical motor. Do not use the dimmer circuit with lamps of over 60 watts. Only standard incandescent lamps will work with this dimmer; compact fluorescent bulbs will not operate.
References
- Photo Credit Jupiterimages/Photos.com/Getty Images
