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[moved] What is the output waveform in the 2nd circuit ? RC vs CR

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Ayman Essam

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i have this question that want me to draw the waveform of both circuits, the 1st is OK, its just an RC delayed version of the original. what about the 2nd ?
1.png
 

CataM

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First one --> low pass filter (LPF)
Second one --> high pass filter (HPF)

Analytical response of HPF: Vout(t)=5·e^(-1000t)


NOTE: In my graphs goes to 1 V because that is the step function. For 5 V means that goes to 5 V the plot. (is the same the transient response, just changes the final value).
 

Audioguru

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You should have learned that in an RC circuit the capacitor charges from the resistor exponentially which is not a delay.
The second circuit is CR where the capacitor cannot charge immediately so it passes the entire 0V to +5V leading edge then it charges into the resistor exponentially.
 

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c_mitra

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Case 1: Initial voltage across the capacitor is zero. The capacitor charges via R and we get an exponential graph that reaches 5V with a time constant determined by RC.

Case 2: Initial voltage across the capacitor is 5V. The capacitor discharges via R and we get a negative exponential graph that reaches zero with a time constant determined by RC.

What do you mean by RC delayed version of the original?
 

Audioguru

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Case 2 is confusing in this thread that has a +5V sudden rise into an RC for A and into a CR for B. The capacitor always begins discharged.
The sudden rise would originally sound like POP. A delayed version would also sound like POP. But the RC cuts high frequencies which would sound like THUD and the CR cuts low frequencies which would sound like TICK.
 

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