Table of Contents
Advertisement
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. (The PXI chassis
has built-in fans to handle 25 W per slot.)
© National Instruments Corporation
Figure 3-6 shows a signal connection example for both sinking and
sourcing current. The example shows a TTL-level application with a supply
voltage of +5 V. The 6527 provides sink current when the relay is closed.
Resistor R
provides source current when the relay is open.
L
When the relay is open, little current flows through the resistor and the
output voltage is close to 5 V, a logic high. When the relay is closed, current
flows through the load and the output voltage is close to 0 V, a logic low. If
isolation is not a concern, you can use the +5 V line from the 6527 device
in place of the external +5 V supply.
Choose a value of R
L
but large enough to avoid reducing sink current or consuming unnecessary
power. For many TTL-level applications, a value of approximately
R
= 5 k works well. This gives a source current at 2.8 V of
L
(5 V – 2.8 V)/5 k = 440 µA. The sink current at 0.5 V is then at least
(0.5 V / 35
– (5 V – 0.5 V)/5 k = 13.4 mA.
+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
(42 V
)
Peak
•
Maximum current (I
small enough to provide the source current you need
6527
35
Isolation
1
) = 120 mA
f
3-11
Chapter 3
Signal Connections
To External +5 V Supply
R
= 5 k
L
V
OUT
I
f
Isolated
Ground
) = 60 VDC
OUT
) = 30 V
OUT
RMS
6527 User Manual
Advertisement
Table of Contents
