© National Instruments
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3-13
RMX Programmable Power Supplies User Manual
External Voltage (Vext) Connection
Use a low-noise, stable voltage source for 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 3-12.
CV Vext Connection.
If you use a shielded cable, connect the shield to the negative output terminal. Refer to
When Controlling the Output with an External Voltage (Vext)
if the shield needs to be connected
to the Vext side. Use pins 22 and 23 of the J1 connector.
Control Using an External Resistance (Rext)
An external variable resistor (Rext) can be used along with the Reference Voltage Output (pin
20 on the J1 connector) to externally control the output voltage of the power supply. You can
use this method to set the output voltage (Eo) to a value from 0% to 105% of the rated output
voltage (Ertg).
To use an external resistance (Rext) to control the output voltage, set CONFIG setting CF06 to
ON to enable control of the output voltage using an external resistor.
The output voltage (Eo) varies in the range of 0 to the rated output voltage (Ertg) 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).
External voltage (Vext)
0 to 5 V (CF07: Lo)
External voltage (Vext)
0 to 10 V (CF07: Hi)
Eo = Ertg × Vext/5 (in V)
Vext = 5 × Eo/Ertg (in V)
Eo = Ertg × Vext/10 (in V)
Vext = 10 × Eo/Ertg (in V)
2-core shielded wire or
twisted-pair wire
Vext
+
–
Output terminals
J1
22
2
3
RMX
