# RC-circuit analysis

Discussion in 'General Electronics Chat' started by win_curese, Mar 24, 2008.

1. ### win_curese Thread Starter New Member

Mar 24, 2008
2
0
Hi, I am new here, just discoverd the site from wikipedia!!

I have a little easy task, that i cannot solve it!

I am dealing with RC-circuit, R = 10KOhm and C=0.1microF
they are connected as high-pass and low-pass filter.

The input voltage are sinusoidal and square wave.

I measured the output using Oscilloscope.

Can anyone analyse the wave form of the output please.

Low-pass and high-pass for both sinusoidal and square input wave.

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
Did you see something that you didn't understand or did not expect?

3. ### mentaaal Senior Member

Oct 17, 2005
451
0
When you say analyse it what exactly do you mean? Do you know how to use complex numbers to analyse circuits? with ac, its most of the rules in dc apply as long as the components are represented with complex numbers. you can work out the impedance of the capacitor using the formula Xc = 1/(2*pi*f*C) then, as the components are in series, their impedances may simply be added (again, only in complex number form) Once this is done, working out currents and voltages are just a simple application of ohm's law. Thats the most of the work done.

4. ### win_curese Thread Starter New Member

Mar 24, 2008
2
0
They are in parallel, just like simple circuit of high-pass and low-pass filter!
What i saw was that there are some phase shift between input and output voltage for sinusoidal and the difference in amplitude. Why there are some phase shift??
The problem arise when i tune the generator to the square wave form, for the low pass filter, the exponential graph occur, and for the high-pass filter there is a jump of output voltage and the size between each peak is doubled of the original input amplitude. Why is it like that??

By the way, thank u very much

5. ### mentaaal Senior Member

Oct 17, 2005
451
0
The reason why there is a phase shift is because there are reactive components in the circuit. In any circuit which has capacitance and/or inductance, the energy storage mechanism of the reactive device serves to phase shift current and voltage.

http://www.allaboutcircuits.com/vol_2/chpt_3/4.html
http://www.allaboutcircuits.com/vol_2/chpt_3/3.html
These links might help you.

With square waves, the amplitude is changing very rapidly at the transistions. The induced voltage from an inductor is proportional to the instantaneous rate of change of the curent through it so if the current is changing rapidly, as is the case of the square wave, the induced voltage may well be higher than the input. ( in fact the voltage can easily be many many times larger than the input amplitude)

I am not sure about the exponential graph, i am only guessing but perhaps as the frequency increases, the rate of change of current is increasing and the induced voltage inceases as a result. (not sure how this turns into an exponential though...)