Capacitors in series instead of single capacitor, why?

Discussion in 'Electronic Basics' started by drgonfly, Nov 7, 2003.

1. drgonflyGuest

I'm a complete newbie to electronics, so sorry is this is a stupid question but
in looking at schematics in an attempt to see how a power supply works, I
notice in some setups, right after the bridge rectifier, people use a single
electrolytic capacitor (3300uf or so), while others use 2 capacitors in series.
Can anyone explain why they don't just use a single capacitor? They are usually
something like 1000uF each, so why not use a single 2000uF capacitor? When is
it better to use 2 capacitors instead of a single cap? Does using 2 capacitors
help smooth out the voltage better then a single capacitor?

Again, sorry if this sounds stupid to you. I'm just trying to learn a little

2. Kevin AylwardGuest

Capacitors are put in series for three main reasons. One to get a
no-preferred value, two, to get double the voltage rating, three, to
make a large bipolar cap from unipolar caps.

Kevin Aylward

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3. John GGuest

2 1000mfd capacitors in series gets you only 500 mfd not 2000 mfd.
The maths would take too long for me to explain.
Resistors in series ADD.

4. John PopelishGuest

In electronics, 'series' has a very specific meaning. Series means
connected start of one to end of other, forming a single path. This
reduces the effective capacitance, but increases the voltage rating.

I am guessing that you are asking about two capacitors connected in
parallel (side by side across the rectifier output rails). Sometimes
capacitors are connected in parallel (which adds their capacity) to
approximate a larger capacitor but one that has a higher ripple
current capability than a single larger unit might have, or to fit the
total capacitance into a space restriction (like keeping the maximum
component height below some limit).

5. Fritz SchlunderGuest

Study the rectifier configuration. Quite often two capacitors are put in
series to perform a voltage doubling function (that is, provide a DC voltage
of magnitude equivalent to the peak to peak voltage of the AC waveform minus
two diode drops). Usually the arrangment is shown where the two capacitors
are stacked vertically on top of each other and the connection between the
two of them goes to one of the transformer's secondary pins. The other
transformer pin of the secondary is then fed to two diodes, one going to the
+ side of the top capacitor (diode cathode to + of capacitor), and the other
going to the - side of the bottom capacitor (diode anode to + of capacitor).
The DC output voltage is then taken from the - side of the bottom capacitor
and the + side of the top capacitor. This can be a handy arrangment.

6. Fritz SchlunderGuest

capacitor).

Whoops. In the last line above replace the "diode anode to + of capacitor"
to "diode anode to - of capacitor".

7. Fred AbseGuest

"Dual voltage" arrangements often use a voltage doubler arrangement for
115 volts and a bridge rectifier for 230 volts, connecting the reservoir
capacitors accordingly.