User Manual

Application ConsiderationsC–2
Circuit Overview
To make sure your signal source and the 1771-VHSC module are
compatibility, you need to understand the electrical characteristics of
your output driver and its interaction with the 1771-VHSC input
circuit.
Refer to Figure C.1. The most basic circuit would consist of R1, R2,
JPR4, JPR5, 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. With JPR4
closed, and JPR5 open, the total limiting resistance is R1 + R2 =
1150 ohms. This jumper position is designated “12 to 24 Volt
Range.” Assuming a 2V drop across the photodiode and R97 and
R98, you would have 8.7-19mA demanded from the driving circuit
as the applied voltage ranged from 12 to 24V.
Figure C.1
Example Circuits for 5V Differential and +12 to +24V SingleEnded
Drivers
R1 R2
C41
JPR4 JPR5
JPR6
JPR7
JPR8 JPR9
JPR10
JPR11
R3 R4
R97 R98
C43
Q2
Q3
D2
D3
D5
D6
R100
R101
R31
R36
C38
C42
+5V
C3 C4
1
2
3
4
5V DIFFERENTIAL
LINE DRIVER
+12 TO 24V
INPUT
HIGH
LOW
DRIVE
DRIVE
1501K
R
1501K
22 ohm
Input Terminals
Voltage Jumpers
V oltage Jumpers
Filter Jumpers
10691I
Drive
Circuit
D1
D4
40.2
40.2
40.2
40.2
+12 TO 24V
SINGLEENDED
DRIVER
In the “5 Volt” position (JPR4 open; JPR5 closed), R1 is shorted and
the limiting resistance is 250 ohms. If 5.0V was applied at the input,
the current demanded would be (5.0 - 2.0)/150 = 20mA.
The above type of calculation is necessary to the user since the
driving device must cause a minimum of 5mA to flow through the
photodiode regardless of which jumper position is selected.