| 摘要 |
PROBLEM TO BE SOLVED: To stop the circuit operation so as to prevent the generation of damages to a lamp due to overheat, deformation of a base and smoking accident of a capacitor by braking a MOS-FET or a constant voltage diode before breakdown of lamp, deformation of the base and smoking accident is generated in the case where the lifetime end condition of the lamp is continued. SOLUTION: An alternating current power source is connected to a full-wave rectifier unit PB through an inrush restricting resistor R1, a filter capacitor C1 and a choke coil L1. A filter capacitor C2 is connected in parallel with an output end of the full-wave rectifier unit PB, and furthermore, connected in series to a MOS-FETQ1 and MOS-FETQ2. Zener diodes ZD1 and ZD2, which are connected in series opposite to each other, are connected between a gate G and a source S of the MOS-FETQ1, and Zener diodes ZD3, ZD4 are similarly connected to the MOS-FETQ2. A lighting circuit having high safety without generating leak and smoking at the end of the lifetime of a lamp can be obtained by setting ON resistance of the MOS-FET to 2 ohm or more and less than 5 ohm. |
