On a DC power supply on the output side of the bridge rectifier is filter capacitor. Could someone tell me what the filter capacitor is doing for the DC output circuit. Also how do I calculate what value the filter cap. should be for a homemade power supply.
thanx Corbyn City George (CCG)
George:
The output from the bridge rectifier is full wave DC - that is it has peaks and troughs. The function of the filter capacitor is to smooth out the waves. The larger the capacitor the more efficient it is in this smoothing. A capacitor has two ratings - voltage and microfarads. You must have a cap with a voltage rating greater than the output of the rectifier bridge. The higher the better but you don't have to go overboard. The microfarad rating is what determines the amount of smoothing. You also want to use a high rating here - 500 to 1000 mfd would probably be adequate but more would be better. I currently use 2 to 3 1000mfd caps in parallel for my DC power supplies. Some of the more electrically minded guys may have other ideas but this has worked for me.
Joe
Thanx for the help. Is there a difference between a filter cap and a standard cap or are they calling it a filter cap because that is just what it is doing
CCG
Store the below link in Favorites. You will refer to it a lot.
http://home.cogeco.ca/~rpaisley4/CircuitIndex.html
There is a section on Power Supplies and Basic Electronics.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Just called a filter cap because it's acting as a filter. They tend to be large in value relative to what a capacitor used for, say, an oscillator would be, but it's the same basic device. They are polarized, so make sure the positive lead connects to the positive leg of the bridge rectifier, and the negative to the negative. The results of hooking it up backwards can be rather - dramatic.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Adding a filter capacitor will rasie the output voltage to about the peak voltage of the input. 12 volts AC input will yield about 16-17 volts DC with a filter capacitor.