| 摘要 |
PURPOSE:To extend the lifetime of a discharge lamp by preheating a filament by a first time constant circuit to fire the lamp, and switching it to a dimming level after the lamp is fired by a second time constant circuit. CONSTITUTION:The emitter potentials of switching transistors 3a-3b are switched to fire to dim a discharge lamp 7, and relay contacts Rya-Ryb are provided in parallel with emitter resistors RE. A relay Ry for turning ON, OFF the contacts Rya-Ryb is connected between the terminals a and a' of a drive power source. A first time constant circuit 9 of a resistor Rb and a capacitor Cb and a time constant switch circuit 10 containing a second time constant circuit 11 is provided in parallel with the relay Ry at this time. The switch circuit 10 also has a relay setting transistor 13 and a selectively connecting manual switch 12. Thus, the circuit 9 takes charge of soft start to reduce its cost. |
