Patent ID: 8330108

Claim:
A power control circuit of variable-frequency opto-interrupter dedicated for printers, comprising: an opto-interrupter having an IR photodiode and an optically-coupled receiving end for penetrating through a printing medium and detecting a thickness thereof; a plurality of impedances mounted by stages in accordance with values thereof, one ends of the plurality of impedances electrically connected with an emitter pin of an phototransistor at the optically-coupled receiving end in parallel, and the other ends electrically connected with relative control pins of an integrated circuit, so that the control pins vary outputs thereof to make the values of the plurality of impedances progressively incremented or decremented in a fixed range; and a variable frequency generator generating variable frequency signals and electrically connected with a negative pole pin of an IR photodiode; whereby an emitting intensity of the IR photodiode is adjusted to penetrate through different printing media so as to acquire a broader dynamic range.