Light adjusting apparatus

A light adjusting apparatus comprising:

• a lamp connected to the output voltage of a commercial a.c. power supply through a switching element,
• a rectifier for directly rectifying the current of the a.c. power supply to generate a d.c. output,
• a switching control circuit operable by the d.c. output of the rectifier for controlling the conduction time of the switching element based on the time of the zero-crossing of the a.c. power supply output voltage, and
• a light adjusting signal generating circuit for producing a pulsewidth modulated light adjusting signal by a light-emitting element,
• the switching control circuit comprising,
• a photodetector for receiving the light adjusting signal from the light-emitting element,
• a demodulation circuit for subjecting the output signal from the photodetector to pulsewidth demodulation, and
• a conduction timing control circuit for controlling the conduction time of the switching element by the output signal of the demodulation circuit,
• the conduction timing control circuit further comprising,
• a voltage adjusting circuit for adjusting the voltage of an output signal from the demodulation circuit in response to the amplitude of the output voltage of the a.c. power supply,
• a zero-cross timing detecting circuit for detecting the time of the zero-crossing of the output voltage of the a.c. power supply,
• a sawtooth wave generating circuit for generating a sawtooth wave having a ramp corresponding to a voltage adjusted by the voltage adjusting circuit in response to the zero crossing detected by the zero-cross timing detecting circuit, and
• a switching timing control circuit for controlling the conduction time of said switching element in response to the ramp of the sawtooth wave generated by the sawtooth wave generating circuit.