basis.
Programming with Variable Voltage Gain
Figure 58 illustrates the method by which the power supply can be programmed using an external voltage with a voltage gain dependent upon the ratio of RP to RR. Note that this method is no different from the circuit normally used for constant voltage control of the output except that an external reference (the programming voltage source) has been substituted for the internal reference.
On most supplies external terminals are available so that the connections shown in Figure 58 can be accomplished without any internal wiring changes. In all Agilent remotely programmable power supplies the summing point S is made available, and the configuration of Figure 58 can always be accomplished using the external programming voltage source and external precision wirewound resistors RP and RR. (RR should not exceed 10K). As indicated by the equation in Figure 58, RP can be selected so that the resulting voltage gain is either less or greater than unity. It is possible to use the front panel control on the supply as the voltage gain control, RP.
Figure 58. Voltage Programming with Variable Voltage Gain
When programming the output using a remote voltage source, the use of a zener diode across the programming terminals will prevent the power supply output from exceeding a predetermined limit, even though the programming source may provide an excessively high input command. The relationship between the zener diode and the output limit value depends upon the power supply design and the programming connection, but in any case can be determined by considering the power supply as equivalent to an operational amplifier. The zener diode must have a current rating equal to or greater than the largest current which the remote programming source can
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