Volatge Regulator -- what type capacitors

Discussion in 'General Electronics Chat' started by mbird, Dec 3, 2013.

  1. mbird

    Thread Starter Member

    Jan 29, 2009
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    Hi --

    This is a followup to a question I posted way back and am now finally revisiting years later...

    I have a Voltage Regulator: ua78m33c.
    It is for powering small, low frequency, simple stuff (like 555 timers, LEDs, etc.) on my breadboard.

    The data sheet does not have application notes but it does have a note in the electrical characteristics section:
    All characteristics are measured with a 0.33-μF capacitor across the input and a 0.1-μF capacitor across the output.

    I was also advised in my last post about this:
    You will also need a larger capacitor on the output of the regulator, in the range of 100uF to 330uF. 555 timers create a momentary short from Vcc to ground when they are changing output states. Unless you have a fairly large "bypass" capacitor, the timer can appear to get "hung up".

    I will add the these three capacitors. My question is what type of capacitors? Is a basic ceramic OK for the small ones and an Electrolytic for the 100uF? Can I (should I?) go outside of these ranges?

    I see on eBay for the 0.33uF I can get either: Dipped Tantalum, Mylar, Multilayer Mono Ceramic, Nippon Chem, Radial Aluminum Electrolytic, Radial Poly, Metalized Polyester, Film Capacitors or Ceramic MLCC -- will they all work or is one preferred over the other?

    Thank you!!!
     
    Last edited: Dec 3, 2013
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You could also go with Tantalum in place of the electrolytic's, especially if you want to decrease the physical size.
    Max.
     
  3. mbird

    Thread Starter Member

    Jan 29, 2009
    24
    2
    I have no 0.33uF and so I see on eBay I can get either: Dipped Tantalum, Mylar, Multilayer Mono Ceramic, Nippon Chem, Radial Aluminum Electrolytic, Radial Poly, Metalized Polyester, Film Capacitors or Ceramic MLCC -- will they all work or is one preferred over the other?

    I do have some small 100uF electrolytics and some basic ceramic .1uF -- will those be OK?

    I need to explore what the different types are used for (or are they all the same and it is just a matter of different types do the same job?)

    Thank you!
     
    Last edited: Dec 3, 2013
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You don't want to use Tantalum in H.F. applications.
    Max.
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    We used Tantalums all the time for HF switchers up to 200 kHz range.

    For regulator input/output caps just use any cheap alum electrolytic bypassed with a ceramic. That way you have plenty of capacitance (more is better)
     
  6. mbird

    Thread Starter Member

    Jan 29, 2009
    24
    2
    Hi --

    So just so I understand... for mine (low frequency) I'll use ceramics for the 0.1uF (output) and .33uF (input) and an electrolytic for the 100uF (output)?

    Thanks for your help!
     
  7. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Sorry about thread jack

    But what is the purpose of the bypass cermaic cap? ??
     
  8. crutschow

    Expert

    Mar 14, 2008
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    That will be fine. You could use a film type for the small caps but typically ceramics are used since they are small and reliable.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    To better bypass the high frequencies that electrolytics don't do well due to their higher parasitic inductance and ESR.
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    0.1μF ceramic on the output is ok.

    You don't need 100μF on the output. Put it on the input side of the regulator.
     
  11. mbird

    Thread Starter Member

    Jan 29, 2009
    24
    2
    >You don't need 100μF on the output. Put it on the input side of the regulator.

    In my original post someone said I would need the 100uF on the output -- should I put it on the output or the input?...
    From original post...
    ...you will also need a larger capacitor on the output of the regulator, in the range of 100uF to 330uF. 555 timers create a momentary short from Vcc to ground when they are changing output states. Unless you have a fairly large "bypass" capacitor, the timer can appear to get "hung up".

    Thanks!
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    I would recommend changing to a CMOS 555 such as TLC555 or LMC555.
     
  13. mbird

    Thread Starter Member

    Jan 29, 2009
    24
    2
    Hi --

    Just to finalize my question on the capacitors...
    for my general low frequency use:
    ceramics for the 0.1uF (output) and .33uF (input) and an electrolytic for the 100uF (output) -- is this OK?

    Thank you!
     
  14. MrChips

    Moderator

    Oct 2, 2009
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    It is not as simple as that.
    What does the 555 timer drive? What else is on the board?
    How much current does the board consume?
    Can you show a circuit diagram?
     
  15. mbird

    Thread Starter Member

    Jan 29, 2009
    24
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    Hi --

    I just want this for playing with the 555 so the use is all kinds of simple 555 experiments. I expect all low frequency and low current stuff (less than 50mA), simple transistor experiments, etc. This is just to have a basic power supply for my breadboard so I can play and experiment with simple electronics circuits. I have a 6 Volt wall power supply but I want to cut it down to 3.3 volts to play with simple digital circuits, etc. all low power all low frequency.

    Thanks for your ideas and help!
     
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If it is just for bread boarding, put a 100uF cap on the power rails of the breadboard (one on each side of breadboard), then put a 100nF (0.1uF) ceramic or tantalum cap across pins 8 and 1 of the 555 (right next to the chip).

    That set up will handle 95% of what you will ever do on your breadboard.
     
  17. MrChips

    Moderator

    Oct 2, 2009
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    NE555 is spec'd to run from 4.5 to 16V.
    TLC555 will run from 2 to 15V.

    I still recommend putting 0.1μF ceramic caps on the input and output pins of the regulator.

    Put one 100μF electrolytic on the output of the 6V wall adapter.

    Put 0.1μF ceramic across power and GND pins of your chips.

    Put one 10μF electrolytic across the breadboard power rails.
     
  18. mbird

    Thread Starter Member

    Jan 29, 2009
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    Thanks for all your help and suggestions. I will use the TLC555 and set up my regulator and breadboard as you indicated.
     
  19. TheComet

    Member

    Mar 11, 2013
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    wtf is this comment

    Never in my life have I heard of having to bypass an LM555 with 100uF. Even the DATASHEET says you only need 100nF ceramic and 1uF electrolytic, see page 10 under "additional information": http://classes.soe.ucsc.edu/cmpe118/Winter13/Labs/LM555.pdf

    While the LM555 will create a momentary current surge when changing output states, it definitely doesn't create a "short" - far from it.

    The voltage regulator's datasheet states you need 0.33uF on the input and 0.1uF on the output. Stick to that, that's all you need.

    The bypass capacitors need to be placed as close as possible to the LM555. The output and input capacitors of the voltage regulator need to be placed as close as possible to the voltage regulator.

    Why is this even relevant to the discussion? As far as our OP is concerned, the TLC555 and the LM555 are nearly identical. He's only bread-boarding everything, these details are superfluous and make things unnecessarily complicated.
     
  20. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I agree with your statements but lets keep off the 'wtf'. It doesn't add to the conversation.

    Cheers
     
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