Voltage Regulators

Discussion in 'The Projects Forum' started by Ata Nams, May 31, 2013.

  1. Ata Nams

    Thread Starter New Member

    May 28, 2013
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    why are Voltage Regulators in between load and filters? And what is the purpose of filters?:) :)
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Because that is how they are used. It's like asking "Why does the sock go between the foot and shoe?"

    You have to be more specific. Can you show a schematic?
     
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
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    To regulate the DC. Filter smooths the pulsating DC so the regulator can work properly.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    A linear voltage regulator is not supposed to pulsate. It is a linear feedback control system. The capacitor on the output pin is to slowdown the response time of the feedback circuit and prevent it from going into high frequency oscillation.
     
  5. Shagas

    Active Member

    May 13, 2013
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    From what I read , the cap on the output is necessary if the output is more than 6 inches from the regulator and my guess is that the capacitance of the wires comes into play at that distance . Am I right?
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    No. On every 3-terminal voltage regulator you need about 1μF at the output pin to GND to prevent oscillation.

    At your load you can add 10μF to 100μF to smooth out load fluctuations.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Almost.. Its the input though not output. 6" or more away from the input filter an input bypass cap should be used.
     
  8. JMac3108

    Active Member

    Aug 16, 2010
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    You also need a minimum cap at the output to prevent oscillation as MrChips said. The minimum value is listed in the datasheet.
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    It's actually the inductance of the wires decoupling the effect of the output cap, but you have the basic idea right. Most linear regs need at least about 1uF of cap within about one cm of the output terminal. Large caps out near the load are to provide peak currents to the loads.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    The OP asked about the the regulator being between the load and filter so he was referring to the input capacitor not the output capacitor. The purpose of that capacitor is to smooth any pulsations from the raw DC source (as wmodavis in post #3 noted). From that point the thread got sidetracked into discussing the output capacitor. :rolleyes:
     
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