Chapter 3
Connecting the UMI-7774/7772 to Drives and Other Devices
National Instruments UMI-7774/7772 User Manual
3-30
ni.com
Figure 3-19.
UMI-7774-7772 Optically Isolated Sinking Input Interface Circuit and
Connection to High-Side Switch
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.
Note
If the load current exceeds the over current trip point minimum of 160 mA when
V
iso
is 30 V, 150 mA when V
iso
is 24 V, or 60 mA when V
iso
is 5 V, the output shuts off.
Disconnect the load to re-enable the input and power on the output.
Ciso
Digital
Input
Viso
Vcc
UMI-7774/7772
High-Side
Limit Switch
Current Limiter
