Why do we need to connect capacitors in Series and sometimes in Parallel?

Question

i wanna know the reason... please help me...

Answer 1

Most of these answers seem to be answering the question of why you would connect capacitors to each other in series or parallel.  If the true intent of the question is to ask why one would connect a capacitor in series or parallel to something else (like a circuit input or output) then it's a different answer.  

Capacitors resist changes in voltage, it takes them time to respond to a changing voltage.

So when connected to two points of a circuit in parallel the capacitor will resist changes in voltage between them such that only the slowly changing portion will make it through.  In the case where one of those connections is say a signal input and the other is ground, then you've made a low-pass filter such that only low frequencies (slowly changing signals) make it through to the input and higher frequencies (quickly changing signals such as noise) are filtered out.  This is a common practice in lots of parts of power supplies, amplifiers, and other circuits where noise and interference need to be eliminated.  This is called DC coupling.  

When connected to a circuit in series the capacitor will work like a high-pass filter, thus removing the low frequency portion of the signal (such as DC component) and allowing the high frequency signal to pass through.  This is called AC coupling and essentially is taking the derivative of the signal such that only the part that is changing passes through and the non-changing portion (where the derivative is zero) gets blocked.   A common application of this is in signal lines that provide DC voltage on the same wire to power the device, such as a microphone.  Many microphones require 48v DC to operate so that is sent down the wire from the mixer/preamp to power the mic, then downstream the series capacitor removes the 48v DC from the line and allows only the microphone signal to pass through to the mixer input without the DC component.  DirecTV and Dish Net satellite dishes work the same way, the receiver sends 13 or 18 volts DC up the line to power the LNB that is receiving the satellite signal.  Back in the receiver an AC coupling capacitor is used to filter out the DC voltage allowing only the satellite signal to pass through to the receiver input.

In general, for both of these applications, the cutoff frequency--the dividing line (and its width) between what passes and what gets blocked--is determined by the value of the capacitor and the impedance of whatever it is connected to.

Answer 2

You would connect caps in parallel to increase the value.

If you needed 200µF and all you had were 100µF units, you can connect two in parallel to get the needed 200µF.

There is very little usefulness in connecting caps in series. In theory, you can increase the operating voltage. If you had only 1000 volt caps and you had an application where you needed 1800 volts, you could put two of the 1000 volt units in series to get a 2000 volt unit, with a C half of either.

But putting caps in series has a problem, in that the voltage rarely divides equally between two caps, even if the capacitance values are the same, because leakage current may be different between the two, and that would shift the voltage division, and may result in one cap's operating voltage being exceeded, and the cap destroyed.

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Answer 3

By connecting capacitors in series you decrease the capacitance of the capacitors in series.  By connecting them parallel you are increasing the capacitance.  This effect works because by essentially adding plates to the capacitor when they are in parallel. Resistors are the opposite. You increase resistance by putting them in series and decrease it by putting them parallel.  Now why would you do this?  It all depends on your design factors.  2 capacitors that add up to the needed capacitance may be less expensive than 1 at the required capacitance.  It also may have to do with what is available to work with.  It may also have to do with updating an initial design to make it work better.  Many times you design a circuit only to find out the theoretical design doesn't work as well in actual built circuit so you have to tweak.

Answer 4

1)capacitors are connected in series the value become reduced say 2 mfd capacitor connected in series resultant value 1 mfd only

Why it is required  example sometime we got  2mfd 5kv capacitor 2 pcs , which we can use it in >than 5 kv supply (6kv or <than 8 kv source) our real requiremwnt is 1 mf 8kv we can use the above capacitor in series these capacitor will work properly same as 1 mfd 10kv capacitor.

2) capacitor connected in parrellel it will added 2+2 = 4 mfd , some tme some huge size single capacitor canno't be mounted in some location (Power supply unit because of compact design) for reducing the size 2 are used even it will be some time safe because of temperature raise in some heat sink location if one is there if damage total failure if 2 pcs are there, both will not DAMAGE AT A TIME .This is simple example I have given In circuit design various factors  applied for fail safe operation.

Answer 5

Abobe two answerers are right about increasing the value of capacitor by connecting them in parallel.

Apart from that capacitors when connected parallel to other devices are used for bypassing AC component, primarily to ensure that Q-point of the circuit does not change. Remember the formula Xc= 1/(2*pi*f*C). Capactor offers very high resistance to DC and low frequency components, and very low resistance to high frequency AC components.

Capacitors offer a low resistance path to AC. Higher is the value of capacitance, lesser is the resistance to the flow of AC.

Similarly, capacitors may be used in series to block the DC component. Remember, we use a capacitor to connect an AC source to amplifier, as we don't want DC to be amplified. DC component, because of zero frequency, are offered infinte resistance and are practically blocked.