DIMMER NOISE REDUCING CIRCUIT OF PIEZOELECTRIC TRANSFORMER

摘要

A dimmer noise reducing circuit wherein vibration noise accompanying the activation/deactivation of a piezoelectric transformer can be reduced, while non-uniformity of brightness of a discharge lamp can be prevented. A chopping circuit turns on/off an output from an input voltage source in a given periodic manner and a full-bridge circuit that receives an output voltage (vb1) of the chopping circuit. An output from a lowpass filter is supplied to a piezoelectric transformer, an output current of which (Io) is supplied to a discharge lamp. The full-bridge circuit is controlled by a full-bridge drive circuit to switch the input voltage (VB1) from the chopping circuit. The drive frequencies of the FETs of the full-bridge circuit are decided by a voltage-controlled oscillator. The chopping circuit is connected to a duty varying circuit the full-bridge circuit is caused to operate with its duty fixed.