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Appendix D
Application Considerations
Examples for Selecting
Input Devices
5V Differential
Line Driver
+12 to 24V
High
Input
Low
+ 12 to 24V
Single-ended
Driver
96
These examples help you determine the best input type for your particular
application. These examples include:
•
5V differential line driver.
•
single-ended driver.
•
open collector circuit.
•
electromechanical limit switch.
Circuit Overview
The circuit overview varies based on module series.
Series A and B Modules
To make sure your signal source and the module are compatible, you must
understand the electrical characteristics of your output driver and its
interaction with the 1756-HSC input circuit.
As shown in the illustration, the most basic circuit consists of R1, R2, the
photodiode, and associated circuitry around half of the opto-isolator. The
resistors provide first-order current limiting to the photodiodes of the dual
high-speed opto-isolator.
When a signal is applied to the 12-24V inputs (pins 13 and 17 in the graphic), the
total limiting resistance is R3 + R4 = 1150 . Assuming a 2V drop across the
photodiode and R7 and R8, you would have 8...21 mA demanded from the
driving circuit as the applied voltage ranged from 12V...24V.
Input Terminals
14
R1
R2
1K
150
16
C1
18
13
R3
R4
R
1K
150
15
22
C2
17
Rockwell Automation Publication 1756-UM007E-EN-P - August 2021
D1
D2
Q1
D3
R5
R6
40.2
40.2
C3
D4
D5
Q2
D6
R7
R8
40.2
40.2
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