Full wave rectifier - smoothing capacitor value?

Thread Starter

drabina

Joined Oct 24, 2008
13
I am building a simple full wave rectifier with smoothing capacitor. I am using the following transformer to drop the input voltage:

in: 120V 65W
out: 12V 4170mA AC

The rectifier bridge is 50V 25A (I also have 400V 8A). The power supply is going to be used for 18W guitar amplifier based on this schematic:

schematic

Since I am still a noob when it comes to electronics, I have have no idea what value the smoothing capacitor should have.

Anybody can help me out?

Thanks.
 

Thread Starter

drabina

Joined Oct 24, 2008
13
Thanks for replies. So if my math is correct, according to Jony130's equation I am getting:

C = (2A * 1/120Hz) / 1V = 0.016F

Is that correct? The amp draws 2A max to produce 18W.
 

jimkeith

Joined Oct 26, 2011
540
Actually, the capacitor may be reduced by the 0.7 factor--jony130's method assumes instant charging--in my method, it is assumed that the transformer supplies the current for 30% of the cycle and the capacitor supplying current for the remaining 70%.
 

Thread Starter

drabina

Joined Oct 24, 2008
13
Thanks again for the replies. I know now how to calculate the smoothing capacitor value! The problem is that the price of 24,000uF cap is somewhere close to $35. I may be better reusing one of my switching power supplies that I have in my project box.
 

kubeek

Joined Sep 20, 2005
5,718
You don´t need a 24000uF cap, you can use for example 5 4700uF caps in parallel. For 35V they should cost like $5 total.
 

jimkeith

Joined Oct 26, 2011
540
In agreement with Jony130, the value is not all that critical--I would add that it does no harm to go larger as well.
 

Thread Starter

drabina

Joined Oct 24, 2008
13
I have few 2200uF caps and maybe one 3300uF. I can probably add up to over 10,000uF with what I have in my parts bin.
 
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