| 摘要 |
PURPOSE:To reduce the stress of switch elements by detecting the phase drift generated in the on-period of the switch element on the low voltage side, and limiting the output at the final stage of the life of a discharge lamp. CONSTITUTION:When a discharge lamp (1) has a half-wave discharge at the final stage of its life, the collector current IC2 nears 0 while a transistor TrQ2 is turned on. The phase of the current IC2 advances with respect to the on-signal of TrQ2. The voltage induced on a feedback winding n3 provided on a current limiting choke L1 also advances. The H-level portion of a Zener diode ZD1 is generated while the output of a buffer gate G4 is the H-level, FF is set, and TrQ5 is turned on. A current flows in a resistor R16, the charging current of a capacitor C7 is increased, and the on-segment of TrQ2 is squeezed by a controller 5. The output of an inverter circuit is reduced, and the stress to circuit components can be reduced. |
