DIMMER NOISE REDUCING CIRCUIT OF PIEZOELECTRIC TRANSFORMER

摘要

A dimmer noise reducing circuit of piezoelectric transformer wherein vibration noise accompanying the activation/deactivation of a piezoelectric transformer can be reduced, while non-uniformity of brightness as in a liquid crystal display using a discharge lamp can be prevented. There are included a chopping circuit (21) that turns on/off an output from an input voltage source (1) in a given periodic manner; and a full-bridge circuit (2) that receives an output voltage (vbl) of the chopping circuit (21) to operate. An output from a lowpass filter (3) is supplied to a piezoelectric transformer (4), an output current of which (Io) is supplied to a discharge lamp. The full-bridge circuit (2) is controlled by a full-bridge drive circuit (5) to switch the input voltage (VB 1) from the chopping circuit (21). The drive frequencies of the FETs of the full-bridge circuit (2) are decided by a voltage-controlled oscillator (9). The chopping circuit (21) is connected to a duty varying circuit (6) such that the full-bridge circuit (2) is caused to operate with its duty fixed.