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I need to find Vout in time domain for below circuit.

Here's my attempt, using Laplace transform.

$$V_{in}(t) = V_0 \sin(\omega t)$$

From the above equation, Vin in s-domain is then:

$$V_{in}(s)=V_0\frac{\omega}{s^2+\omega^2}$$

And Vout in s-domain is as follows:

$$V_{out}(s)=V_{in}(s)\times \frac{\frac{-1}{C_1s}}{R_1}=V_{in}(s)\times\frac{-1}{R_1C_1s}$$

Subsitituting Vin(s) in the equation above, we get:

$$V_{out}(s)=\frac{-V_0}{R_1C_1}\frac{1}{s}\frac{\omega}{s^2+\omega^2}$$

With partial fraction, it becomes:

$$V_{out}(s)=\frac{-V_0}{R_1C_1}[\frac{1\over\omega}{s}+\frac{-s\over\omega}{s^2+\omega^2}] =\frac{-V_0}{R_1C_1\omega}[\frac{1}{s}+\frac{-s}{s^2+\omega^2}]$$

Convert back to time domain, it becomes:

$$V_{out}(t)=\frac{-V_0}{R_1C_1\omega}[1-\cos(\omega t)]=\frac{V_0 \cos(\omega t)}{R_1C_1\omega}-\frac{V_0}{R_1C_1\omega}$$

The answer key from the book is:

$$\frac{V_0 \cos(\omega t)}{R_1C_1\omega}$$

Where did I do wrong?

schematic

simulate this circuit – Schematic created using CircuitLab

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1 Answer 1

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Not worry ... Made with Maple.

Here are the two results plotted.
You can see that the first (Vot, low curve) is with "DC" added, and the other is without "DC" ...

The answer in the book is just the "AC" component.
You are just "right" with transient response.

enter image description here

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  • \$\begingroup\$ I figured it out. That DC component is the "constant" part. The book solved it by using current through the capacitor, which is integral of dV/dt, and taking the integral, gives the reuslt + the constant, but the book ommitted the constant. \$\endgroup\$ Commented Mar 21, 2024 at 19:49

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