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Dual Supply Voltage Divider

Schematic of a dual supply, or two input, voltage divider.

    Enter a value for Vin A, Vin B, and Vout to find the optimal resistor values that yield the specified Vout. You can optionally enter a value for R1 or R2 with Vin A, Vin B, and Vout if you want to fix the value of one of the resistors. Entering both R1 and R2 with Vin A and Vin B will calculate Vout. If over specified (R1, R2, Vin A, Vin B, and Vout are entered), the values of R1 and R2 are ignored. Note that in all cases, Vin A and Vin B must be specified. Both Vin A and Vin B can be positive or negative. In most cases, Vin A will represent a positive voltage and Vin B will represent a negative voltage or vice versa.

    In addition to the resistor values presented as standard values in five tolerances, the range of expected voltages is found.  The effect of the resistors tolerance is included in the voltage ranges indicated.

    Resistive voltage dividers are amoung the most common circuit configurations used. In most cases, voltage dividers are used to derive a voltage from single input voltage. In this case, the solver provides a solution when there are multiple input voltages (such as the positive and negative supplies common in may analog circuits). If you have single supply voltages, as is the case in some analog circuits, the “Single Supply” solver is more appropriate. In some case, such as scaling a signal level for input to an ADC or amplifier, it is more convenient to think of the ratio, or the magnitude that the input is reduced by to produce an output, than the absolute voltage level. In that case, the “Resistor Ratio” solver is your best choice.

    As is the case with all resistive voltage dividers, placing a load on Vout will change the output level. Unless Vout is very lightly loaded (for instance the input of a non inverting op-amp or other high impedance load) you may need to buffer its output first. If you wish to lower the resistances found to minimize loading effects, one convenient strategy is to divide the value of R1 and R2 by ten. The resulting values will still be standard values in the original tolerance.

This solver uses the following equation to compute its values:

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