Photocoupler with improved anti-noise characteristics

A photocoupler which has a light generating section for converting an input signal into light and a light receiving section for converting the light from the light generating section into a signal and releasing the signal after having the signal subjected to a delay until at least the input signal becomes stable, comprising:

• light receiving means for receiving light from the light generating section;
• converting means for switching an output thereof from Low to High upon receipt of light by the light receiving means;
• oscillating means for generating a clock signal;
• an updown counter for counting the clock signal within 0 and a preset number, and switching an operation thereof between counting-up mode and counting-down mode according to an output of the converting means;
• decoder means for switching an output thereof from Low to High when a counted value of the updown counter reaches a preset number after the updown counter started a counting-up operation in response to a first level change from Low to High of the output of the converting means;
• keeping the output thereof High until the preset number is counted down to "0" after the updown counter started a counting-down operation in response to a second level change from High to Low of the output of the converting means;
• switching the output thereof from High to Low when the counted value equals to zero;
• and forming an output of the photocoupler as its own output;
• and
• clock signal supply control means for supplying a clock signal to the updown counter since the first level change until a full-count state of the updown counter;
• and supplying the clock signal again to the updown counter since the second level change until the full-count value of the updown counter is counted down to "0",
• wherein the light receiving means, the converting means, the oscillating means, the updown counter, the decoder means and the clock signal supply control means are monolithically integrated.