© National Instruments | 3-15RMX Programmable Power Supplies User ManualControl Using an External Voltage (Vext)To use an external voltage (Vext) to control the output current, set CONFIG setting CF05 to ONto 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 externalvoltage (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 groundterminal. The signal must be floating relative to ground. Connecting/referencing thissignal to ground may cause the cable to be damaged. Refer to Figures 3-10 and 3-11for more information.Pay careful attention to the polarity of Vext. Do not apply a voltage of 10.5 V orgreater, or a reverse voltage across the external voltage control pins.External voltage source (Vext) connectionConnect a low-noise, stable voltage source to Vext. The noise in Vext is multiplied by theamplification 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 itsspecifications.To reduce the noise on the output, connect a 2-core shielded wire or a twisted-pair wire, and keepthe wire as short as possible. If the wiring between the RMX programmable power supply andthe external contact is long, it becomes easy for noise to influence the operation of the RMXprogrammable power supply. Even if you use cables that are designed to suppress noise, theRMX 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 ortwisted-pair wireVext +– Output terminalsJ12123RMX
