Agilent Technologies 90B Dual Output Using Resistive Divider, Reverse Current Loading Problem

DUAL OUTPUT USING RESISTIVE DIVIDER

Often it is required to use both a positive and negative dc power source having approximately the same voltage and current capability. It might seem reasonable to meet such requirements using a single regulated dc supply with a resistive voltage divider center-tapped to ground. Figure 65 shows, however, that such an arrangement results in a drastic increase in the effective dc source impedance feeding each load; assuming that the power supply has a zero output impedance, each load looks back into a source impedance consisting of the two arms of the voltage divider in parallel with each other and the other load resistance.

Figure 64A. Reverse Current Loading Problem

Thus, a change in the current requirement of either load results not only in a change in its own dc voltage, but also in a change of the dc voltage feeding the other load, and extreme conditions of imbalance can develop. In many cases, a simultaneous need for positive and negative dc voltages necessitates the use of two separate regulated power supplies.

94