| 摘要 |
PURPOSE:To prevent unpleasant blinking of a discharge lamp in its termination period and lower power source consumption at starting time of lighting by installing a circuit to detect the termination of a discharge lamp and lowering resonance electric current of an inverter with an output from the circuit. CONSTITUTION:A discharge lamp 20 is operated by high frequency sent from an inverter circuit 8. A detecting coil 28 is rolled on an inductor 19 for a ballast and a termination detecting circuit 55 and a resonance current lowering circuit 56 are successively connected to the inductor 19. The termination detecting circuit 55 is composed of capacitors 57, 58, resistors 59, 60, a Zener diode 61, and a transistor 62. A light-emitting part 65 of photocouplers 63, 64 forming a part of a resonance current lower circuit 56 is connected to a transistor 62. In termination period of a lamp, voltage of the detecting coil 28 rises, the light- emitting part 65 is electrically conducted, serial resonance current of the inductor 19 and the capacitor 23 is decreased, and the inverter circuit 8 is protected. Electric power source for abnormality detection of a discharge lamp is obtained from the detecting coil 28 therefore another safety circuit is not needed, resulting in save of electric power. |
