Is it possible to use this single supply, non-inverting, summing op-amp configuration to sum multiple arbitrary DC voltages at unity gain?
I've used the inverting summing op-amp config on bipolar power supplies to sum AC and DC input voltages (paired with a second op-amp to 'un-invert' them) but this is my first time trying to do the same thing with a single supply, non-inverting config – and I'm struggling with how the R values are interacting.
Needs to be this config as it will be running off a single 12V supply but I don't need anything past whole number precision for the DC summing and how close the op-amp can get to GND or VCC is also not that important at this stage.
In this first example – I get the expected output. +5V at input R3 and +2.5V at input R4 gives me +7.5V at VOut.
But in the second example – if I disconnect either one of these inputs – I start getting a gain of 2x at the output i.e. just +5V at input R3 gives me +10V at Out.
How can I configure this so adding or removing outputs will always give me a gain of 1x?
Thanks
Best Answer
The inverting summer sums current. The non-inverting summer attempts to sum voltage but the source resistances of the other inputs form a voltage divider.
If you choose the resistors so that a loss of a factor of 3 occurs then the non-inverting gain of 3 will compensate.
When a non-inverting input is removed, it must be connected to zero volts I order to maintain the voltage divider.
simulate this circuit – Schematic created using CircuitLab