# What is the avg current flowing from B to A.

#### circuitking

##### Full Member level 5
Hi can anyone tell me what is the avg current flowing from B to A in the attached figure.
I just gave some random values for voltages and capacitance.
Please tell how to theoretically find it.

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Clue -

Regards, Dana.

##### Super Moderator
Staff member
The gating waveforms imply that one Nmos is on when the other Nmos is off.

#### KlausST

##### Super Moderator
Staff member
Hi,

It can only be solved with
* non overlapping square waves
* non ideal switches

Then it's easy, since C = As/V

Klaus

#### FvM

##### Super Moderator
Staff member
The gating waveforms imply that one Nmos is on when the other Nmos is off.
Yes, the capacitor is alternatingly charged and discharged. The solution is found by applying elementary capacitor equations.

I = Q * f = C * V * f

No matter if the switches are ideal or not, if you don't worry about infinite current.

#### KlausST

##### Super Moderator
Staff member
Hi,

The problem with ideal switches - better say ideal devices - that you can't calculate with energy and power...
Because of the capacitor-capacitor problem.

If there is average current flow from B to A with a given supply voltage, then power needs to be dissipated somewhere.
If the capacitor is without ohmic loss, and the switches are without ohmic loss .... where does the power go?

Klaus

#### FvM

##### Super Moderator
Staff member
If the capacitor is without ohmic loss, and the switches are without ohmic loss .... where does the power go?
You are right. Some switch resistance is required for final duration of charge/discharge.

#### circuitking

##### Full Member level 5
Hi all, I didn't understand what is the answer. Is it CVf?

##### Super Moderator
Staff member
The exercise isn't quantifiable the way it's drawn... Rather the intention (I suppose) is to answer by explaining circuit behavior.

The transistors conduct at mutually exclusive times. Result:

1) Some current flows from the upper supply to charge the capacitor.

2) Some current discharges from the capacitor toward the bottom supply.