| 摘要 |
PURPOSE:To prevent a load from the inflow of abnormal current and burning precisely by interrupting load current if the load current is made to flow in spite of no trigger of a semiconductor control rectifier element. CONSTITUTION:When a two-way thyristor 4 is normally operated by a trigger signal applied to a terminal 5, a Tr40 is not turned on. If the thyristor 4 is turned on in spite of no application of a trigger pulse to the terminal 5, electrostatic charge is accumulated in a capacitor 39 because a self-holding circuit 36 is in the off status, and when voltage between both the terminals of the capacitor 39 exceeds the total voltage of the voltage between the base and emitter of the Tr40 and the Zener voltage of a Zener diode 41, the Tr40 is turned on. At the abnormal time, the ON of the Tr40 causes large current flow into a fuse 42 and a resistor 43, so that the fuse is disconnected, current flow into a relay 30 is interrupted and current flow into the load 3 is also interrupted.
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