Specifications
A test system with many
Failsafe-type switches requires
a significant amount of current
to maintain switch closures.
Some RF /Microwave Switch
Drivers can actually drive over
20 A of current to control
these types of switches. They
require a high-current power
supply and the routing of
relatively high-gage wires to
and from the driver module,
power supply, and switch.
Switch manufacturers provide
latching-relay switches that
only require a 10-20 ms pulse
of current to change the state
of the switch. This doubles the
number of coils in the switch
housing, increases the size of
the switch housing, and adds
cost. However, wiring and
power requirements will be
much easier to implement.
Test engineers and operators of
test systems often need visual
feedback to understand and
troubleshoot the test system.
Without position feedback
hardware inside the switch, it
can be difficult to determine
the switch’s actual state. LED
indicators are also commonly
mounted on an operator panel
to indicate the active signal
path. Position feedback is
usually read by digital inputs
and use separate digital outputs
to drive LEDs.
Some vendor’s Switch Drivers
are really just high current
Digital Output hardware. They
only energize the relay coil,
so position feedback and LED
drivers must be provided by
additional Digital Input and
Output hardware. Add this to
the complexity of power distri-
bution, and you end up with an
expensive solution that is also
difficult to troubleshoot when
failures occur.
Controlling Agilent
Switches and Attenuators
The Agilent 34945A/L4445A
Switch/Attenuator Driver is
optimized to drive Agilent
switches and attenuators,
although it can be used to
drive virtually any discrete
switch or attenuator. This
section will show you how
to select options for Agilent
switches and attenuators to
configure the most efficient
and easy-to-use system. Here
are the recommended attributes:
• 24 V latching, relay coils
configured for open-collector,
pulsed-mode operation
• Position Feedback to sense
the actual state of the switch
• D-sub connector mounted
on device to simplify wiring
RF/Microwave switches/
attenuators are most often
24 V devices, and there is good
reason. 24 V coils draw signifi-
cantly less current than 12 V
or 5 V coils. In many cases, you
actually pay more for 12 V or
5 V coils. Selecting 24 V relay
coils simplifies this process and
permits you to drive switches
without an external power
supply when connecting to
the first 34945EXT module.
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