Patent ID: 8618743

Claim:
A dimmer including: a switching circuit having a switching element and being serially connected to an alternating-current (AC) power source and a lighting load; and a time division control circuit for controlling an effective voltage supplied to the lighting load by regulating the period of time to turn on the switching element, and the dimmer further comprising: a) a zero-crossing detector for detecting a zero-crossing point at which a voltage of the AC power source becomes zero and for generating a zero-crossing signal whose value changes at the zero-crossing point; b) an oscillator for generating an oscillating signal having a frequency equal to a frequency of the AC power source or an integral multiple of the frequency of the AC power source; c) a reference point determiner for measuring a phase difference between the zero-crossing signal and the oscillating signal every time the zero-crossing signal is generated, and for determining a reference point for setting a timing of turning on or off the switching element based on a data of a measured value of the phase difference; and d) a time division control signal generator for sending to the switching element an on/off signal for turning on or off the switching element, at the timing determined on a basis of the reference point and the effective voltage to be supplied to the lighting load.