Wiring I/O Units
Section 3-5
Output Surge Current
When connecting a Transistor or Triac Output Unit to an output device having a
high surge current (such as an incandescent lamp), care must be taken to avoid
damage to the Output Unit. The Transistor and Triac Output Units are capable of
withstanding a surge current of ten times the rated current. If the surge current
for a particular device exceeds this amount, use one of the following circuit con
-
figurations to protect the Output Unit.
OUT
L
+
R
COM
The above circuit protects the Output Unit by letting the load draw a small current
(about one third the rated current) while the output is OFF, significantly reducing
the surge current. The following circuit reduces the surge current by employing a
current-limiting resistor.
R
OUT
L
+
COM
Transistor Output Residual
Voltage
A Transistor Output Unit’s output cannot be directly connected to a TTL input
because of the transistor’s residual voltage. When connecting TTL circuits to
transistor Output Units, connect a pull-up resistor and a CMOS IC between the
two.
3-5-3 Wiring Examples
The following examples illustrate how to connect I/O devices to I/O Units. During
wiring, work slowly and carefully. If an input device is connected to an Output
Unit, damage may result. Check all I/O devices to make sure they meet the spec
ifications (refer to Appendix B Specifications). Be sure to allow for leakage cur
rents and load inductance.
-
-
Input Units
DC Input Units
Contact output
IN
DC input
COM
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