Why is large capacitor always followed by small capacitor?

[yahaa]

capacitance problem

in a rectifier circuit why is the large capacitor always followed by a small capacitor????????
whats the purpose of the 2 capacitors??????

 

[satya_vijayawada]

Re: capacitance problem

to reduce the ripple, a large capacitor (high Value )required.

 

[ptmsl]

Re: capacitance problem

The reason for putting a small capacitor in parallel with the bulk is that large electrolytic capacitors have large ESR and low resonant frequency so you put a small capacitor in parallel for high frequency decoupling.

 

[yahaa]

Re: capacitance problem

can u avoid the jargons and expain it in detail .......plz ?????

 

[v_c]

Re: capacitance problem

As ptmsl said, large electrolytic (polarized) capacitors are only capacitive at low frequencies. As frequencies get higher and higher they actually start behaving more like inductors! So if to have capacitance at higher frequencies you use smaller capacitors in parallel (to add to the capacitance). By the way, these smaller capacitors are usually of different type (for example ceramic) so they have much lower equivalent series resistance and higher resonant frequency (they are behave as capacitors up to higher frequencies).

Does this help?

Best regards,
v_c

 

[artem]

capacitance problem

http://www.analog.com/library/analogDialogue/Anniversary/21.html
http://www.ecircuitcenter.com/Circuits/cmodel1/cmodel1.htm

 

[elantra]

capacitance problem

yeah, artem provided information userful for you.
normally the capacitance is not a pure capacitance, it has esr, esl and so on.