Keysight Technologies L4490A, Руководство пользователя

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42 Keysight L4490A/L4491A User’s Guide
Hardware Configuration Instrument Configuration
External Supply
Each 34945EXT can support up to 2A continuous using 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 second (slave) 34945EXT module or both, the supply must be able to provide
the quiescent current requirement of the EXT module(s), plus the quiescent 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.
The second consideration regarding the external supply are the quiescent current
and switching current specifications of the switch. Using the Keysight
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
The quiescent current required when switching does not occur is:
[34945EXT quiescent current from 24V] + [87104 / 87106 switch quiescent current]
[24V: 1.2W / 24V = 50 mA ] + [ 50 mA ] = 100 mA
For a single 34945EXT driven by an external supply, the current required for
actuating a 87104/87106 switch is:
[34945EXT quiescent current from 24V] + [switch quiescent current] + [switching
current]
[24V: 1.2W / 24V = 50 mA ] + [ 50 mA ] + [ 200 mA ] = 300 mA (15 ms pulse, 100 mA
qui.)