| 摘要 |
PURPOSE:To prevent the breakdown of an electric device by actuating a protecting element if a constant voltage element is defectively released. CONSTITUTION:When a switch 2 is closed, a 100V AC power supply 1 undergoes full-wave rectification by a rectifier 5 and is turned into a pulsating current. This current is applied to a constant voltage diode 5 via a resistance 7 for voltage drop and clipped by 5V Zener voltage. The clipped pulsating current is smoothed by a smoothing accumulator 6 and change into voltage of a constant level. This constant voltage of 5V is supplied to an electric device 11. In this case, if a low voltage diode 8 has a release defect owing to application of large electric power higher than 400mW to the diode 8, a 5V constant voltage operation is not obtained. Therefore >=5V power is applied to a varister 9, and a large current flows into the varister 9 since this varister has the negative resistance that has a sudden reduction of resistance at >=8V power level. Thus the applied voltage of the device 11 is suppressed to about 8V. |
