# Grounds in AC circuit

I am trying to solve for Vo in the circuit above. The input voltage is a simple sinusoidal with Vp = 100V. And all R=2.2k . What I am confused about is how to deal with the two grounds. How do grounds work in an AC circuit in the first place? The -ve side will not always be at 0V. I'm not sure how to go at this problem.

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This can't be answered without knowing how the two AC signals are related to the ground. Otherwise, it first helps to draw the schematic more logically. That may make certain things more obvious. Then I'd start analyzing at the two extreme cases where the AC signals are at their positive and negative peaks. – Olin Lathrop Feb 14 '14 at 14:35

## 2 Answers

If you ignore the small volt drop across the forward conducting diodes and assumed in reverse, the diodes were perfect you'd find that Vout was half of Vin: -

It always helps if you draw out the flow of currents then rearranged the circuit.

Reading the comments, I have assumed that the AC voltage source is floating with respect to ground.

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Thank you, these diagrams help a lot. You treated the grounds as simply being connected to each other, and then forgot about about them when dealing with the equivalent circuits. That definitely showed me how to go at this type of problems! – Sebolains Feb 14 '14 at 15:11
Note that this solution is only valid if the incoming AC signal is floating with respsect to ground. We don't know whether that is the case. – Olin Lathrop Feb 14 '14 at 15:15

What I am confused about is how to deal with the two grounds.

The circuit can be redrawn as follows:

simulate this circuit – Schematic created using CircuitLab

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So I guess my question now becomes whether currents flows towards the ground or the negative (during positive duty cycle) in this case. – Sebolains Feb 14 '14 at 14:46
@Sebolains, the ground symbol simply designates the reference node which is, by definition, the node with 0V. You can solve this problem just fine without it; remove it in the above schematic if it is distracting you. The voltage $V_o$ is simply the voltage across the right-most resistor. – Alfred Centauri Feb 14 '14 at 14:54
This redrawing makes the HUGE assumption that the AC voltage source is floating. If it's the secondary of a transformer, that's OK. Otherwise, ... not. – Brian Drummond Feb 14 '14 at 14:58
@BrianDrummond, it's not a huge assumption, it's a perfectly reasonable assumption for the information given. – Alfred Centauri Feb 14 '14 at 15:07
If the grounds only designate a reference, that should make my life a bit easier. I definitely know how to go at this problem now, thank you! – Sebolains Feb 14 '14 at 15:10