©
National Instruments Corp.
7
FP-DO-400 and cFP-DO-400
Protection for Inductive Loads
When an inductive load, such as a motor or relay, 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 output and the power supply.
It is best to limit flyback voltages by installing a flyback diode
across an inductive load. Typically, you should mount the flyback
diode within 18 in. of the load. Figure 4 shows one channel
connected to an inductive load with a flyback diode.
Figure 4.
Digital Output Circuit (External Power Supply Not Shown)
The [c]FP-DO-400 contains flyback diodes to prevent excessively
high voltage from damaging the module. National Instruments still
recommends using an external protection circuit across any
inductive load.
Table 3.
Common Output Configurations
Channel Subset
Channel Subset
Total A
2
8 channels @ 1 A
—
8 A
2
5 channels @ 1.25 A
—
7.81 A
2
4 channels @ 1.25 A
3 channels @ 0.75 A
7.94 A
2
3 channels at 1.5 A
1 channel @ 1 A
7.75 A
2
COM
V
OUT
V
SUP
V
C
Flyback Diode
for Inductive Load
[c]FP-DO-400
Load
1.5 A max
