Electrical – voltage divider with 2 power sources, Vout

voltage divider

schematic

simulate this circuit – Schematic created using CircuitLab

If V2 is NOT present(VB=GND) i can solve it easily using voltage divider formula:
I know the steps:

  1. I = V1/(R1+R2)
  2. Vout = I * R2 =>(i have 'I' from step 1,R2 is known)=> Vout = (V1*R2)/(R1+R2)

Questions:

  • A) I would like to request some help on how to solve it when v2 = 3.3 volts is
    present. Please do not skip steps if you answer it.

    B) Vout is calculated with reference to GND. Right? If yes, that means
    the voltage drop at R2 equals to Vout = Vout – GND = Vout – 0 = Vout
    assuming GND as reference point?

    C) Is it correct to say the voltage drop at R2 = Vout – VB? (So in
    this case i do not take GND as a reference point).

    D) So there are 2 different ways to describe voltage drop? Like case B) and
    case C).Am i correct?

Best Answer

The key is voltage ACROSS the resistive chain

V = V1 - V2

Then it is a simple voltage divider to work out the voltage across R2

Vr2 = V(R2/(R1+R2))

Finally the output is raised by V2

Vout = Vr2 + V2

Thus. Vout = (V1-V2)(R2/(R1+R2))+V2

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