 ### Network # Electrical circuit Analysis

Feb 19, 2021
677
My analysis of the circuit is since 5V is connected to both ends of the circuit there will be no current flow. Is it correct?

No, the transient source, V2, is not constantly at 5V

Regards, Dana.

#### crutschow

May 7, 2021
794
the transient source, V2, is not constantly at 5V
There is a transient analysis specified, but both V1 and V2 are shown as being a constant +5V.

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#### crutschow

May 7, 2021
794
My analysis of the circuit is since 5V is connected to both ends of the circuit there will be no current flow. Is it correct?
Yes.
Did you do the simulation to check?

#### crutschow

May 7, 2021
794
I get 0 Amp.
Is it that i shall not do transient analysis for constant voltage supplies?
Yes, you can do transient analysis with constant voltage supplies.
Why would you expect other than 0 amps?
Can I assume this also as 0 amp current since it is in fA?
Yes, that value is approaching the precision of the Spice calculations.
I don't understand the behavior.
What don't you understand?
With zero voltage across the components (the same signal from both sources) you get essentially zero current, as would be expected.
If you want to see some significant current, then make one source a DC voltage.

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#### electronicsLearner77

Jul 2, 2015
306
What don't you understand?
With zero voltage across the components (the same signal from both sources) you get essentially zero current, as would be expected.
If you want to see some significant current, then make one source a DC voltage.
Since the current seem to be fluctuating increasing and decreasing instead of a straight line.
If you want to see some significant current, then make one source a DC voltage.
Yes i am trying that i will show.

#### crutschow

May 7, 2021
794
Since the current seem to be fluctuating increasing and decreasing instead of a straight line.
But that's a very tiny current, likely to the limits of the computing precision in the simulator.
No matter how many digits the current is computed too, it may never be exactly zero.

#### crutschow

May 7, 2021
794
I have applied inverted PWM's, now the current amplitude is bigger.
So are you happy with those results?

• electronicsLearner77

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,476
Your calculations are good in the first part (0 ms -> 1 ms).

In the second part (1 ms -> 2 ms), however, you ignore the term (v1-v2)/r and use the result from part 1 to calculate a decaying current. What is your reasoning for doing so?

Consider instead $i(t) = \frac{(v_1 - v_2)}{R} \times (1 - e^{(-\frac{t}{\tau})})$ for $t \rightarrow \infty$

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• electronicsLearner77

#### electronicsLearner77

Jul 2, 2015
306
Your calculations are good in the first part (0 ms -> 1 ms).

In the second part (1 ms -> 2 ms), however, you ignore the term (v1-v2)/r and use the result from part 1 to calculate a decaying current. What is your reasoning for doing so?

Consider instead $i(t) = \frac{(v_1 - v_2)}{R} \times (1 - e^{(-\frac{t}{\tau})})$ for $t \rightarrow \infty$
The circuit i have drawn and the results i am getting are completely mismatch, i think the circuit is wrong or the spice is not doing the simulations properly.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,476
or the spice is not doing the simulations properly.
I suggest you look at your own calculations first before blaming it on SPICE.

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