# Smoothing output of a full bridge

#### anistorian

Feb 23, 2018
7
Hello!

Hope someone want to help me a little bit. I was wondering, when I view schematics of a full bridge rectifier, the smoothing capacitor always seem to be non-polarized. I guess that is to let the output of the cap go into the positive rail of the rectifier output. Is that a correct assumption ? And in that case, would it be possible to use a polarized cap in series with a diode instead? Or would the voltage drop be too significant for that to work?

#### kellys_eye

Jun 25, 2010
6,514
The smoothing capacitor is probably only shown as non-polarised for a theoretical appreciation rather than a practical one.

The size of smoothing capacitor is usually defined by the current draw (rule of thumb is 1000μF per amp-drawn) and you won't find capacitors of that size in a non-polarised package - unless you;re prepared to pay big money.

Not sure what you're going on about when you state

would it be possible to use a polarized cap in series with a diode instead? Or would the voltage drop be too significant for that to work?

#### anistorian

Feb 23, 2018
7
• The smoothing capacitor is probably only shown as non-polarised for a theoretical appreciation rather than a practical one.
Okay, so a polarized one would actually be used in most cases? Bear with me, I'm pretty new to this haha
• Not sure what you're going on about when you state
Maybe it's because I'm not actually sure how a capacitor work. I assumed that when you hook up the anode of the cap to the positive rail, it would spit out its charge on the kathode. And thereby smoothing the DC right before the end of the negative rail. But maybe it's the other way around ?

#### Bluejets

Oct 5, 2014
6,922
Diagram explains it......Note that this is half wave but full wave works the same.
Cheers Jorgo

#### Attachments

• rectifier.jpg
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#### dave9

Mar 5, 2017
1,188
By being after the bridge rectifier the polarized capacitor is already in series after a diode (two actually), so adding another would be a redundant loss of another ~ 0.7V for no reason.

#### davenn

Moderator
Sep 5, 2009
14,260
Okay, so a polarized one would actually be used in most cases?

in ALL cases

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