Patent ID: 7548708
Filing Date: 2009-06-16
Classification: G03G

Abstract:
1. A power supply unit in an image forming apparatus, comprising: a piezoelectric transformer; an output voltage detecting circuit configured to detect an output voltage of said piezoelectric transformer; an output voltage control circuit configured to control an output voltage from said piezoelectric transformer, said output voltage control circuit comprising a comparator configured to receive an output voltage setting signal, together with an output voltage detecting signal fed back from said output voltage detecting circuit, to compare the output voltage setting signal and the output voltage detecting signal; and a driving frequency supplying circuit configured to generate a driving frequency signal of said piezoelectric transformer in accordance with a comparison result by said comparator, and to supply the driving frequency signal to said piezoelectric transformer, wherein a time constant of said output voltage control circuit is longer than a time constant of said output voltage detecting circuit.