Patent ID: 6373232
Filing Date: 2002-04-16
Classification: G03G,G05F,H03K

Abstract:
A power supply device used in an image forming apparatus, comprising:a first IGBT (Insulated Gate Bipolar Transistor) connected to a power supply; first electricity accumulation means series-connected to said first IGBT; a second IGBT series-connected to said first electricity accumulation means; magnetic field generation means connected between the power supply and a node between said first electricity accumulation means and said second IGBT; second electricity accumulation means parallel-connected to said second IGBT; first rectifying means parallel-connected to said first IGBT; voltage resonant converter means having second rectifying means parallel-connected to said second IGBT; and insulated driving circuit means for shaping a waveform of a transmission voltage transmitted via an output terminal of an insulated transformer, and outputting the transmission voltage as a driving voltage for driving gates of said first and second IGBTs, said insulated driving circuit means having: threshold voltage generation means for generating a preset threshold voltage; detection means for detecting that the transmission voltage becomes lower than the threshold voltage when the transmission voltage drops; and first switching means for short-circuiting output terminals of the insulated transformer in response to the detection.