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Capacitor questions (newbie)

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Hi all,

1. Is there ever a use for putting capacitors in series with each other? Since it reduces the total capacitance, wouldn't it just be a useless thing to do?

2. When a capacitor is used to pass AC and block DC current, I know that the waveform is shifted out of phase. Is there ever a use for this?

3. If the current going in is a sine wave, is the waveform on the other side of the capacitor also a sine wave?

4. If the capacitor does not have enough capacitance to admit the whole AC wave, what does the resulting waveform look like?

Richard
 

RCinFLA

Well-Known Member
1) sometimes to get higher voltage capability. Usually have high value resistors in parallel to help keep the voltage distributed between two caps. Also used in RF design, like putting a variable cap in series with a fixed to modify tuning cap range.

2) Tone control, low frequency attenuation.

3) Yes, may be attenuated and phase shifted for lower frequencies.

4) Again, low frequency attenuation and phase shift. A square wave will sag across its peaks.
 
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Diver300

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Most Helpful Member
Hi all,
2. When a capacitor is used to pass AC and block DC current, I know that the waveform is shifted out of phase. Is there ever a use for this?

There is only significant phase shift near the cut-off frequency. If you have a large enough capacitor, the phase shift will be just about zero.

For example, if you have an audio amplifier with a 10 kΩ input impedance, and you put a 100 µF capacitor in series to block the DC, then the cut off frequency is well under 1 Hz. If you use that for audio in the 20 Hz to 20,000 Hz range, you really won't see any phase shift.
 

audioguru

Well-Known Member
Most Helpful Member
A "phase-shift oscillator" uses the 60 degrees phase-shift from three RC parts to oscillate. The RC parts also filter away the clipping harmonics from the first opamp so the output has low distortion.
 

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