Fluorescent tube is connected in the LC resonant circuit composed of L2 and C9. Bidirectional breakdown diode VD4 is starting circuit. When AC power is connected, VT2 gate potential increases by VD4; when the voltage exceeds the gate threshold voltage, VT2 is conducted. Thus, the resonant current folws C8, fluorescent wire, resonant capacitor C9,
choke L2, the winding of drive transformer Tl by +25 V DC voltage, and the oscillation cycle is decided by C9, L2, and T1. Before the light iturning on, the resonant state is decided by the C9, L2, and VT1, VT2.