| 摘要 |
PURPOSE: To ensure that a load drive means is prevented from operating in an abnormal mode after the supply of AC power is stopped by causing a voltage to quickly drop when the supply of AC power is stopped, so that before the load drive means and a load fail, the control means is stopped. CONSTITUTION: When a commercial AC power supply E is stopped, a voltage at the inverted input terminal of an operational amplifier OP drops, while a voltage at the non-inverted input terminal of the amplifier OP decreases as a smoothing capacitor C1 discharges. When the time required for the potential of the C1 to drop to a voltage at which an inverter circuit 22 and a fluorescent lamp FL do not operate normally is Ta and the time required for the potential to drop to a voltage at which a control means 24 does not operate normally is Tb, Tb is kept at not more than 20m sec and not more than Ta. Therefore, before the circuit 22 and the lamp FL fail, the voltage of the control means 24 quickly drops and the control means is stopped, thus ensuring that after the supply of the power E is stopped an instantaneous flash is prevented from arising and that the inverter circuit 22 is prevented from entering an abnormal mode. |
