# rectifier filter circuits

#### antony.prathiban

Joined May 14, 2008
24
can we use 940 microfarad capacitor directly into the circuit instead of placing more number of capacitors in series and parallel.actually i have a pcb which is having 8 capacitors(400v,470 microf).can we replace it by a single capacitor.what are the considerations?

#### Pich

Joined Mar 11, 2008
119
What is the voltage oued on the board?
Sounds to me it's a combination of series parallel circuit, 4 caps in series parallel with 4 more. So the new cap would need to be 940uf rated at 1600 volts. I don't know if you can buy one and if you could I imagine it would be very expensive.

#### SgtWookie

Joined Jul 17, 2007
22,210
Capacitance in series is calculated like resistors in parallel.
Ctotal = 1 / ( 1 / C1 + 1 / C2 +... 1 / Cn )
Capacitance in parallel is calculated like resistors in series (ie: additive)

Large capacitors have greater ESR and parasitic inductance than smaller capacitors.

#### Pich

Joined Mar 11, 2008
119
right you are Wookie my mistake

#### jblueink

Joined May 27, 2008
24
first of all you have to find out if the capacitor are in series or parallel.if in series use this formula to find the resultant or equvalent value:1/C=1/C1+1/C2+1/C3....BUT if in parallel you have to use this formula:C=C1+C2+C3....the equvalent you calculated should have the same voltage as the ones on the PCB.

#### antony.prathiban

Joined May 14, 2008
24
i gave the resultant value of the capacitors only.
and my question was ,can we reduce the number of capacitors by higher values?and how it is decided?

#### hgmjr

Joined Jan 28, 2005
9,029
i gave the resultant value of the capacitors only.
and my question was ,can we reduce the number of capacitors by higher values?and how it is decided?
Since the designer has elected to use multiple capacitors in parallel, there is probably a good reason from doing so. Most likely it is as several members have already commented, the caps have been paralleled to minimize the ESR. This is typically the reason for multiple paralleled caps. Replacing the caps with a single cap of the same "equivalent" value is likely to adversely impact the circuits performance.

hgmjr