| 摘要 |
A power supply protection circuit for stopping a power supply to electrical equipments in case a normal power voltage is not outputted from a direct current power supply and an excess voltage or a reduced voltage is outputted. The power supply protection circuit according to the present invention is constituted of a power source line 2 for supplying a direct current power, via relay contacts 3a and 3b of a relay, to a electrical equipment 15, a first circuit 10 for detecting an excess voltage and a reduced voltage, a second circuit 20, and a relay operation circuit 25. In the first circuit 10, when a first excess voltage-detecting element 14 detects an excess voltage, a first semiconductor-switching element 12 becomes unconductive, and when first excess voltage detecting element 14 does not detect an excess voltage, a first semiconductor-switching element 12 becomes conductive. In the second circuit 20, when a second excess voltage-detecting element 4 detects an excess voltage, a second semiconductor-switching element 6 becomes conductive, and when a second excess voltage-detecting element 4 does not detect an excess voltage, a second semiconductor-switching element 6 becomes unconductive. The relay operation circuit 25 is constituted of a coil 3c making the relay contacts 3a and 3b of the relay ON/OFF, a third semiconductor-switching element 7 that controls the operation of the coil 3c, and a reduced voltage detecting element 5 that detects a reduced voltage. When an excess voltage is detected by the first excess voltage detecting element 14 and the second excess voltage detecting element 7, if there occurs that a reduced voltage detecting element 5 detects a reduced voltage, the third semiconductor-switching element 7 is made unconductive, and an electric current conducting over the coil 3c is suspended and the relay contacts 3a and 3b of the power source line 12 is turned OFF.
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