| 摘要 |
A photocoupler output signal receiving circuit includes a first constant current circuit (switching elements MP1 and MP2 and current sources I1 and I2), connected between an input terminal 124 and the high potential side of a direct current power source, that discharges current, a second constant current circuit (a current source 13), connected between the input terminal 124 and the low potential side of the direct current power source, that takes in current, and switching elements NM1 to NM3 that operate the first and second constant current circuits in a complementary way, wherein the switching elements NM1 to NM3 are operated so that current is taken in by the second constant current circuit after a photocoupler 21 is turned on, and are operated so that current is discharged by the first constant current circuit after the photocoupler 21 is turned off, and a discharge current value in a current discharge period is reduced after a certain period elapses from the start of discharging. Because of this, an increase in photocoupler lifespan is achieved, with noise resistance secured, and without increasing light emitting diode current. |
