High stability dimmer

Abstract

The present invention is aimed at providing a dimmer capable of preventing malfunctions due to noise contamination or waveform distortion of the voltage of an AC power source. The dimmer according to the present invention has a time division control circuit for controlling an effective voltage supplied to a lighting load by regulating the period of time to turn on a switching element, and further includes: a zero-crossing detector sectionfor detecting a zero-crossing point and generating a zero-crossing signal whose value changes at the zero-crossing point; an oscillatorfor generating an oscillating signal having a frequency equal to that of the AC power source or an integral multiple of this frequency; a reference point determiner sectionfor 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 the timing of turning on or off the switching elementbased on a data of the measured value of the phase difference; and a time division control signal generator (on/off timing calculator sectionand time division control signal generator section) for sending an on/off signal to the switching elementat the timing determined on the basis of the reference point and the effective voltage to be supplied to the lighting load.