Simple 300W lamp dimmer

This simple lamp dimmer uses only a triac (tri-ac), a diac (diac), and a few other passive components to control the lamp's power. It works with 230V incandescent lamps up to 300 watts. Initially, Triac TR1 is not conducting; capacitor C1 charges through resistor R1/potential P1 until the trigger level of Diac D1 is reached. When the Diac trigger level (approximately 30 volts) is reached, D1 triggers, and Triac TR1 is turned on. Triac will remain in conducting mode until the mains current is lower than Triac's holding current at the end of a half-cycle. This works for both negative and positive half-cycles because both Triac and Diac are bidirectional. R1 protects the potentiometer in case of a short circuit. A fuse is absolutely necessary because the discharge arc in a faulty incandescent lamp is almost a short circuit.