Overcurrent Protection - National Instruments 6527 User Manual

Chapter 3 Making Signal Connections

Overcurrent Protection

6527 User Manual
The following equation shows the minimum sink current when V
0.5 V:
 0.5V
----------- -

35 Ω
+5 V
390
Digital
Logic
Figure 3-6. Signal Connections for Driving TTL Voltages
The maximum power ratings for the output channels on a 6527 device are
as follows:
Maximum DC voltage across the terminals (V
Maximum AC voltage across the terminals (V
Maximum current (I
1
With all relays carrying 120 mA and all inputs driven to 28 V, the total power dissipation
can approach 20 W. The maximum switching capacity in PCI and CompactPCI systems
must be derated according to the ambient temperature and cooling capacity of your system
to prevent the device from overheating. (The PXI chassis has built-in fans to handle 25 W
per slot.)
The 6527 device outputs include circuitry to protect them from currents
over the specified range. When excessive current flows through the relay,
the relay increases resistance. Once the current level drops back under the
specified range, the relays return to normal operation.
( )
 5V 0.5V –
– ---------------------------- - =

5 k Ω
6527
35
Isolation
)
f
3-12
OUT
13.4 mA
To External +5 V Supply
R = 5 k
L
V
OUT
I
f
Isolated
Ground
) 60 VDC
OUT
) 30 V
OUT RMS
(42 V )
Peak
1
120 mA
is
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