Help with decoupling

Discussion in 'The Projects Forum' started by eswara1997, Feb 1, 2014.

  1. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    Hello all,

    Working on two oscillators built on one ttl ic. Frequencies at about 460kHz. What should i use to decouple/bypass to prevent gates from syncing up. Size of capacitors and exactlywhere...

    Thank you
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Decoupling caps are in the range of
    1. 10uf to 100uf
    2. 100nf ceramic

    Both caps are used. That is one electrolytic and one ceramic
    They are always soldered close to the IC power supply pins. As close as possible.
    In the case of multiple IC's, a 100nf cap for each IC across the Power pins and 1 common electrolytic across the Power input pins.
     
  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    If you want to decouple two oscillators, you will need decoupling resistors and capacitors for each oscillator.
    In the following PDF of page 15 there is an example on decoupling some amplifier stages:
    RF-proto.pdf

    Bertus
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Wait.
    Was OP talking about something else?
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When the oscillators are in the same chip, you can not decouple them seperately.
    You will need two chips and use the techique I have given in post #3.

    Bertus
     
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  6. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    is soldering a must need? Can i just get it really close and be fine.
    and my capacitors just connect to pin 14 and pin 7? nothing to gnd?
     
  7. R!f@@

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    Soldering or bread board don't care. Need good connections, no loose connections.

    As close as possible.

    Pin 7 is ground on most TTL Gate IC's
     
  8. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    yes so do i connect from 7 to 14.
     
  9. R!f@@

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    Yup. Best if you can connect the 100nf right across pin 14 and 7
     
  10. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    there's no replacement for a 100nf is there? Radio shack doesn't carry it and i'll have to wait a few days to get it. darn.
     
  11. R!f@@

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    Apr 2, 2009
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    100nf Works best.

    Just what the data recommends. I never used any other value. But I guess it all depends the frequency the TTL is switching
     
  12. paulktreg

    Distinguished Member

    Jun 2, 2008
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    They seem to show plenty on their website. Any 0.1uF polyester film capacitor will do but 0.15uF or 0.22uF would probably do at a pinch.
     
  13. R!f@@

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    Apr 2, 2009
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    100nf is 0.1uf.

    Ceramics are best for high frequency by passing.
    Polyester might be best for audio applications
     
  14. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    whoops i didnt convert to uf.
    so for the electrolytic capacitor there's a range of values to select. How do i choose which value between 10-100 uf.
     
  15. R!f@@

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    I would do this
    10uf for around 1 - 3 TTLs
    22uf if more than 3 TTL's
    47uf if more than 10 TTL's
    100uf for more.

    Some thing like that. It all depends on ur application and it's operation.
    These depends on how good the supply is filtered and what types of PSU is used and how far it is located.

    The Ceramics are 1 for each IC. Not more most of the time.
     
  16. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    wait so what about the electrolytic. Isn't that one per ic also.
     
  17. paulktreg

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    One electrolytic across your supply rails.
     
  18. R!f@@

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    Nope. The electrolytic is used to just in case the supply is a bit far away. Say 4 to 6 inches

    It's advisable to use them to filter low frequencies. You don't need one for each IC. Most of the time a 10uf is enough / 5 TTL's or Just one 100uf at the Power supply pins ( across the power input pins where the Power comes into the PCB )
     
  19. eswara1997

    Thread Starter Member

    Dec 14, 2013
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    so where do i connect the electrolytic. i thought 14 to 7. but if so which ic.
     
  20. R!f@@

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    Apr 2, 2009
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    At the power tracks which supplies power to the IC or IC's.
    Close to IC if you use one IC.

    But Mostly at the Power input connector will do just fine
     
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