IDEC MicroSmart - Manual (Page 109)

3: I NSTALLATION AND W IRING
« FC4A M ICRO S MART U SER ’ S M ANUAL » 3-15
Contact Protection Circuit for Relay and Transistor Outputs
Depending on the load, a protection circuit may be needed for the relay output of the MicroSmart modules. Choose a pro-
tection circuit from A through D shown below according to the power supply and connect the protection circuit to the out-
side of the CPU or relay output module.
For protection of the transistor output of the MicroSmart modules, connect protection circuit C shown below to the transis-
tor output circuit.
Protection Circuit A
Protection Circuit B
Protection Circuit C
Protection Circuit D
Inductive Load
COM
C
R
Output Q This protection circuit can be used when the load impedance is
smaller than the RC impedance in an AC load power circuit.
R: Resistor of approximately the same resistance value as the load
C: 0.1 to 1 µF
Inductive Load
COM
R
Output Q This protection circuit can be used for both AC and DC load power
circuits.
R: Resistor of approximately the same resistance value as the load
C: 0.1 to 1 µF
C
+
or
–
Inductive Load
COM
Output Q This protection circuit can be used for DC load power circuits.
Use a diode with the following ratings.
Reverse withstand voltage: Power voltage of the load circuit
× 10
Forward current: More than the load current
+ –
Inductive Load
COM
Output Q This protection circuit can be used for both AC and DC load power
circuits.
+
or
–
Varistor