| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of components, and realize high efficiency by providing a pre-stage voltage step-up chopper of a sub-E class voltage resonance type inverter, and constant current-controlling a cold cathode tube using a voltage resonance type frame IC. SOLUTION: A step-up chopper circuit consists of a choke coil L1, a power MOSFET Q2, a diode D1, and a capacitor C1, and a step-up voltage becomes an input voltage to a sub-E class voltage resonance type inverter. An IC1 is equipped with a function as a voltage resonance type control IC controlling the gate circuit of a power MOSFET Q1, and the control function of the power MOSFET Q2. This IC is driven by a VCO, an operational amplifier 1, and a switching frequency modulation circuit. A oscillation frequency is increased as a Toff , which is set so as to meet a semi-E class operation, is kept constant, and the on time of a switch is reduced so that the feeding current of a cold cathode tube CFL1 is reduced, and constant current control is maintained. |
