| 摘要 |
PURPOSE: To prevent a safety circuit from malfunctioning when power is on and off so as to enhance the reliability of a device by operating the safety circuit only when a detection means detects some abnormality. CONSTITUTION: Even if a transistor Q1 is operating while power is off, the discharge current of a capacitor C5 does not pass through a resistance R10 but flows to the Q1 from the C5 via a diode D8 and a resistance R7 and, even if the Q1 is turned on for a short time, a trigger current is not supplied to an SCR 1 and the SCR 1 does not operate while the power is off. Therefore, no current is supplied to a photocoupler PC. A threshold voltage Vth at which the SCR 1 conducts is set by the R10 and by a Zener diode ZD1. As a result, the power can be turned on again immediately after being turned off. |
