| 摘要 |
PROBLEM TO BE SOLVED: To surely start a discharge lamp using a simple circuit even if a power supply is turned on and off at short intervals. SOLUTION: While a discharge lamp 4 is on, a control circuit 3 lowers the impedance of the base circuits of transistors Tr1, Tr2, thus controlling their ON period to make it longer. When the power supply is turned off, switching of the transistors Tr1, Tr2 is stopped, a capacitor C2 discharges gradually via a resistance R4, but the control circuit 3 keeps the impedance of the base circuits low. If the power supply is turned on under this condition, the terminal voltage of the capacitor C1 rises, and a transistor Tr3 is switched on and causes the capacitor C2 to discharge complately, thus allowing the control circuit 3 to return to its initial state to enhance the impedance of the base circuits and to reduce the ON widths of the transistors Tr1, Tr2. Thereafter, the terminal voltage of the capacitor C1 further rises, allowing switching of the transistors Tr1, Tr2 to smoothly start always in the preheating mode. |
