Photocoupler output signal receiving circuit

A photocoupler output signal receiving circuit that receives an output signal of a photocoupler wherein a signal output from a light emitting unit is transmitted to a light receiving unit in an isolated state, and a pull-up resistor is connected to the output side of the light receiving unit, the output signal receiving circuit being characterized by comprising:

• a first constant current circuit, connected between an input terminal into which the output signal is input and the high potential side of a direct current power source, that discharges current to the light receiving unit;
• a second constant current circuit, connected between the input terminal and the low potential side of the direct current power source, that takes in current from the direct current power source;
• and
• switching elements that operate the first and second constant current circuits in a complementary way, wherein
• the switching elements are operated so that current is taken in by the second constant current circuit after the photocoupler is turned on, and are operated so that current is discharged by the first constant current circuit after the photocoupler 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.