Wiring an Isolated Output
The digital isolated output circuits source current to external loads.
When an inductive load, such as a relay or solenoid, is connected to an output, a large counter-
electromotive force may occur at switching time due to energy stored in the inductive load.
This flyback voltage can damage the outputs and the power supply.
To limit flyback voltages at the inductive load, install a flyback diode across the load. Mount
the flyback diode as close to the load as possible. Use this protection method if you connect
any of the isolated outputs on the IC-3121 to an inductive load.
The following image shows an example of an isolated output wired to an external load with a
flyback diode installed across the load.
Caution
Do not draw more than 35 mA from each isolated output when V
ISO
is
5 V. Do not draw more than 80 mA from each isolated output when V
ISO
is 24 V.
Figure 11. Connecting an Isolated Output to an External Load
Digital Output
External Flyback
Diode for
Inductive Loads
V
ISO
C
ISO
V
CC
Industrial Controller
Load
Overcurrent
Protection Circuit
Connecting to Differential I/O
The IC-3121 accepts differential (RS-422) line driver inputs. Each of the two differential I/O
can be configured as an output. Use shielded cables for all applications. Unshielded cables are
more susceptible to noise and can corrupt signals.
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IC-3121 User Manual