| 摘要 |
When a forward direction voltage of any of several LEDs 14 to 20 is lowered, a drain voltage of an NMOS transistor 70 employed in any of series regulators 24 to 30 becomes higher than a defined voltage. A zener diode ZD1, which is connected to the LED where the abnormal condition occurs, becomes conductive. A voltage, which is increased from the defined voltage, is applied to a negative input terminal of a comparing amplifier 72, and an output voltage of the comparing amplifier 72 is lowered by this increased voltage portion so that a gate voltage of the NMOS transistor 70 is lowered. A current flowing through the NMOS transistor 70 is decreased. Even if an abnormal condition caused by a voltage drop occurs in any of the LEDs 14 to 20, then the LEDs 14 to 20 can be protected.
|
