Positive And Negative Voltage Power Supply

This circuit provides a precision voltage source that can be adjusted through zero to positive a

nd negative voltages, which eliminates reversing connections on the power supply. Also, it is possible to get exactly 0 V, without some offset. As to how this circuit works, first consider the -1 V/V to +1 V/V linear gain-control amp (see the figure). A Burr-Brown INA105 difference amp is used in a unity-gain inverting amp configuration. A potentiometer is connected between the input and ground. The pot"s slider is connected to the noninverting input of the unity-gain amp; this input is typically connected to ground. With the slider at the bottom of the pot, the circuit is a normal-precision unity-gain inverting amp with a gain of -1.0 V/V ± 0.01% maximum. With the slider at the top of the pot, the circuit is a normal-precision voltage follower with a gain of ± 1.0 V/V ± 0.001% maximum. With the slider in the center, there"s equal positive and negative gain for a net gain of 0 V/V. The accuracy between the top and the bottom will usually be limited by the accuracy of the pot.

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