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2
Hardware Configuration
Using the 34945A internal +24V supply, the current required for actuating a
87104/87106 switch is:
[87104 / 87106 switch quiescent current] + [87104 / 87106 switching current]
= 250 mA
CAU T ION
External Supply
Each 34945EXT is limited to 2A continuous current from an externally
connected power supply (4.75V to 30V). The actual amount of power required
by each EXT module depends on the types of switches used.
When using an external power supply with either the master 34945EXT
module or slave 34945EXT modules (required) or both, the supply must be
able to provide the quiescent current requirement of the EXT modules, plus
the quiescent (continuous) and switching currents of the switches themselves.
The power requirement of the 34945EXT is 1.2W. For supported external
supply voltages of 24V, 12V, and 5V, the current required for a single EXT
module is as follows:
current = power / voltage
24V: 1.2W / 24V = 50 mA
12V: 1.2W / 12V = 100 mA
5V: 1.2W / 5V = 240 mA
If multiple EXT modules are driven by a single external supply, the power
required from the supply increases by 1.2W for each EXT module present.
Thus, if two 34945EXT modules are driven by a single supply, the power value
in the previous equations becomes 2.4W - doubling the current requirement.
The second consideration regarding the external supply are the quiescent
current and switching current specifications of the switch. Using the Agilent
87104/87106A, B, C coaxial switches from the internal supply example, the
switch specifications again are:
Supply current (switching: pulse width =15 ms:Vcc = 24 VDC): 200 mA Nom
Supply current (quiescent): 50 mA Max
24
[50 mA]
(15 ms pulse, 50 mA quiescent)
The combination of switches and their power requirements often make it difficult
to determine if the capacity of the 34945A internal +24V supply will be exceeded.
If overcurrent conditions occur repeatedly regardless of recovery time (Chapter 5),
the use of an external power supply as the channel drive source may be required.
Agilent 34945A Microwave Switch/Attenuator Driver Module User's Guide
+
[200 mA]
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