3: I
NSTALLATION
AND
W
IRING
FC5A M
ICRO
S
MART
U
SER
’
S
M
ANUAL
FC9Y-B1268
3-17
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
protection circuit from A through D shown below according to the power supply and connect the protection circuit to the
outside 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 tran-
sistor output circuit.
Protection Circuit A
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
Protection Circuit B
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
–
Protection Circuit C
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
+
–
Protection Circuit D
Inductive Load
COM
Output Q
This protection circuit can be used for both AC and DC load power
circuits.
+
or
–
Varistor
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