Patent ID: 6400096
Filing Date: 2002-06-04
Classification: H05B,Y02B

Abstract:
A control circuit for a piezo transformer based power supply for a fluorescent lamp, comprising:driver circuitry operative to generate pulse waveforms for excitation of primary inputs of the piezo transformer, the driver circuitry comprising four switching transistors arranged as a full bridge with respect to the primary inputs of the piezo transformer, the switching transistors including a first pair for providing a positive pulse waveform to the primary inputs of the piezo transformer and a second pair for providing a negative pulse waveform to the primary inputs of the piezo transformer; a first feedback circuit operative to detect the magnitude of current in the fluorescent lamp and to vary the frequency of the pulse waveforms generated by the driver circuitry so as to maintain a predetermined desired current in the fluorescent lamp; and a second feedback circuit operative to detect the magnitude of the voltage across the primary inputs of the piezo transformer and to vary the duty cycle of the difference between the pulse waveforms generated by the driver circuitry so as to maintain a predetermined desired voltage across the primary inputs of the piezo transformer, the second feedback circuit comprising phase shifting circuitry operative to vary the phase of drive signals supplied to the second pair of switching transistors with respect to the phase of drive signals supplied to the first pair of switching transistors to effect the varying of the duty cycle of the difference between the pulse waveforms.