| 摘要 |
PURPOSE:To attain sure short-circuit protection by connecting a series connected body with a current limit transistor (TR) conducted at impression of voltage and an overcurrent detection resistor across a protection circuit and providing a triggering two-terminal switching element conducted when a voltage across the overcurrent detecting resistor reaches a prescribed voltage so as to close the current limit TR. CONSTITUTION:Since a large current flows to a protection circuit 6 and a voltage across a resistor R2 for detecting an overcurrent reaches a prescribed value or over if an overcurrent flows to a load or the load is short-circuited, a switching diode SD4 is turned on so as to decrease a gate voltage of an FET1. The FET1 is turned off and a short-circuit current flowing through a diode bridge 3 and a thyristor 8 is interrupted. When the cycle approaches a zero cross point after the end of the half cycle of AC, a voltage across the switching diode SD4 of the protection circuit 6 becomes a prescribed voltage or below. Since a capacitor C5 supplies a holding current to the switching diode SD4, the switching diode SD4 keeps ON-state. |
