High-stability dimmer

A dimmer for controlling an output of each of N sets of lighting loads (where N is an integer equal to or greater than two), comprising:

• a) a total of N switching circuits, with one switching circuit serially connected between an alternating-current (AC) power source and each of the N sets of lighting loads;
• and
• b) a single time division control circuit for separately controlling each effective voltage supplied to each of the N sets of lighting loads, by regulating a period of time to turn on each of the N switching circuits,
• the time division control circuit including:
• b-1) a single zero-crossing detector for detecting a zero-crossing point which is a point in time where 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-2) a single oscillator for generating an oscillating signal having a frequency equal to a frequency of the AC power source or to an integral multiple of the frequency of the AC power source;
• b-3) a single 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, based on data of measured values of the phase difference, a reference point to be used in setting a timing of turning on or off each switching circuit, the reference point being common to the N switching circuits;
• and
• b-4) a time division control signal generator provided for each of the N switching circuits, for transmitting, to the switching circuit, an on/off signal for turning on or off the switching circuit, at a timing determined based on the reference point and the effective voltage to be supplied to the lighting load.