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POSITIVE_AND_NEGATIVE_VOLTAGE_POWER_SUPPLY

2014-11-29 08:51  
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POSITIVE_AND_NEGATIVE_VOLTAGE_POWER_SUPPLY
This circuit provides a precision voltage source that can be adjusted through zero to positive and nega-tive 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 witha gain of -1.0 V/V 10.01% maximum. Withthe 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.