| 摘要 |
PROBLEM TO BE SOLVED: To provide a highly efficient small-sized inverter circuit, which does not produce much noise at a low cost, without requiring auxiliary boosting means for a piezoelectric transformer. SOLUTION: Switching elements Q1 and Q2 are driven with control signals S1 and S2 from a control circuit 5 and switch the direct current from an input terminal 10 upon which a DC voltage Vin is applied. A capacitor C1 and a choke coil L1 constitute a first-stage resonance circuit section and the inter- electrode capacity C2 between a choke coil L2 and a piezoelectric transformer T1 constitute a next-stage resonance circuit section. The transformer T1 is driven at the resonance frequency generated from the two stages of serial resonance circuits. A resistor R1 is installed for detecting a tube current IL flowing to a cold cathode tube 4 and controls the switching frequencies of the switching elements Q1 and Q2, by applying negative feedback to the control circuit 50. Consequently, the drive voltage of the transformer T1 is changed, and the outputted power is controlled correspondingly to the changed drive voltage. |
