Inductive Loads Connected To Umi-7774/7772 - National Instruments UMI-7774 User Manual

Chapter 3 Connecting the UMI-7774/7772 to Drives and Other Devices
High-Side
Limit Switch
Note If the load current exceeds the over current trip point minimum of 160 mA when
V is 30 V, 150 mA when V
iso
Disconnect the load to re-enable the input and power on the output.
National Instruments UMI-7774/7772 User Manual
Viso
Current Limiter
Digital
Input
Ciso
UMI-7774/7772
Figure 3-19. UMI-7774-7772 Optically Isolated Sinking Input Interface Circuit and

Inductive Loads Connected to UMI-7774/7772

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
because of the energy stored in the inductive load. This flyback voltage can
damage the outputs and the power supply. You must limit flyback voltages
at the inductive load by installing a flyback diode across the load.
Typically, you mount the flyback diode as close to the load as possible.
Use this protection method if you connect any of the Enable outputs or
general-purpose digital outputs on the UMI-7774/7772 to an inductive
load. Refer to Figure 3-20 for an illustration of the interface circuit for a
general-purpose digital output that is connected to an external device with
a flyback diode.
is 24 V, or 60 mA when V
iso
Connection to High-Side Switch
iso
3-30
Vcc
is 5 V, the output shuts off.
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