1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Full Wave Bridge Rectifier

  1. Jun 28, 2008 #1
    Sometimes in Full Wave Bridge Rectifier circuits a small value capacitor is placed in parallel to the RC block at the output, such as the circuit diagram in the attached jpg. C1 has a much greater value than C2, and the result value of the parallel capacitors is almost the same.
    Can anybody please help me out with this, what is the purpose of the of the small capacitor, I have been asked this question and I can’t find the proper answer, I have tried simulating the circuit with & without the extra capacitor on Multisim, but couldn’t find any difference.

    Thanks a lot for your time.
    Schnitzer
     

    Attached Files:

    • FWBR.JPG
      FWBR.JPG
      File size:
      10.7 KB
      Views:
      104
  2. jcsd
  3. Jun 29, 2008 #2

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    R with C1 will have a larger time constant and R with C2. You can think of it as two low pass filters. With C1 you can remove the ripple (120Hz) and with C2 you can remove higher frequency noise. Check out Decoupling capacitors.

    Welcome to PF
     
  4. Jun 30, 2008 #3
    The impedance of the electrolytic capacitor increases with frequency... so while it's great at 120Hz, it's not so good at higher frequencies.

    The small capacitor compensates for this at the higher frequencies.

    The property of electrolytic capacitors involved is the ESR, equivalent series resistance, which is important when you select capacitors for things like switch mode power supplies which typically run at a lot more than 120Hz.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?