© National Instruments
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3-15
RMX Programmable Power Supplies User Manual
Control Using an External Voltage (Vext)
To use an external voltage (Vext) to control the output current, set CONFIG setting CF05 to ON
to enable control of the output current using an external voltage.
The output current (Io) varies in the range of 0 to the rated output current (Irtg) when the external
voltage (Vext) is changed in the range of 0 to 5 V (CF07: Lo) or in the range of 0 to 10 V (CF07: Hi).
Caution
The Vext cable must not be referenced/connected to the chassis ground
terminal. The signal must be floating relative to ground. Connecting/referencing this
signal to ground may cause the cable to be damaged. Refer to Figures 3-10 and 3-11
for more information.
Pay careful attention to the polarity of Vext. Do not apply a voltage of 10.5 V or
greater, or a reverse voltage across the external voltage control pins.
External voltage source (Vext) connection
Connect a low-noise, stable voltage source to Vext. The noise in Vext is multiplied by the
amplification factor of the RMX programmable power supply and appears in the output.
A noisy Vext source can cause the output ripple noise of the RMX power supply to not meet its
specifications.
To reduce the noise on the output, connect a 2-core shielded wire or a twisted-pair wire, and keep
the wire as short as possible. If the wiring between the RMX programmable power supply and
the external contact is long, it becomes easy for noise to influence the operation of the RMX
programmable power supply. Even if you use cables that are designed to suppress noise, the
RMX programmable power supply may not operate properly.
Figure 3-14.
CC Vext Connection.
External voltage (Vext)
0 to 5 V (CF07: Lo)
External voltage (Vext)
0 to 10 V (CF07: Hi)
Io = Irtg × Vext/5 (in A)
Vext = 5 × Io/Irtg (in A)
Io = Irtg × Vext/10 (in A)
Vext = 10 × Io/Irtg (in A)
2-core shielded wire or
twisted-pair wire
Vext
+
–
Output terminals
J1
21
2
3
RMX
