Is there a more stable 555 timer available?

Discussion in 'The Projects Forum' started by bytraper, Nov 12, 2010.

  1. bytraper

    Thread Starter Active Member

    Sep 28, 2010
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    Ive been working with one of Bill's schematics for his 555 designs (thanks for sharing your knowledge Bill)

    Anyway Ive been reading that the 555 can drift when it gets warm with the pwm and the frequency, is there a version of the 555 thats more resilient to heat?

    Thanks for any replies and help
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I think the drift is mainly dependend on the quality of the capacitor.
    If you want to read more about capacitors, take a look at this website:
    http://my.execpc.com/~endlr/index.html

    Bertus
     
  3. mik3

    Senior Member

    Feb 4, 2008
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    It can drift but the drift may be acceptable by the design. You have to determine the allowable frequency and duty cycle drift.
     
  4. Artikbot

    Member

    Nov 7, 2010
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    1
    One rated at a higher temperature? I'm currently thinking about the military grade 555s. Expensive, but if paired with adequate components (like bertus said, good capacitors, aswell as ultralow tolerance resistors), it can provide a very very very drifting.

    I'm using one in an astable configuration, 10kHz, high quality cap and 20% tolerance resistors (they suck I know xD), and it works just fine. Temperature isn't much of an issue, it drives a MOSFET's gate. I never felt it with any temperature above ambient, to be honest. And it has the HUGE mosfet's heatsing right above.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Also a higher quality of potentiometers will help.
    There are some of Bourns that are quite good.

    Bertus
     
  6. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    If you find the capacitors are the cause of your drift and you know for example they have a positive temperature coefficient then you can find a resistor with a negative temperature coefficient to conteract it.

    Also if the drift of a 555 timer is too great then maybe you should be looking at a more stable clock source. Temperature compensated crystal oscilators would be better.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    I have to agree with WinKilla on this one. The problem is not with with the 555 per se, but with the whole class of RC type circuits. RC oscillators are just not that stable, and the 555 represents the maximum effort to make them so.

    Pay special attention to your other parts such as capacitors (especially the caps) and the resistors and you should be good. The power supply should be well filtered (as well as all the digital type chips having filter caps next to them) and stable on the voltage.

    If none of this is enough you need a different class of circuit, (again as WinKilla suggested). Roman Black has some nifty ideas on his web site to take his crystal oscillators to the next step, and shows how to build a crystal oven around a simple crystal oscillator.

    http://www.romanblack.com/xoven.htm

    Warning, this engineers site is quite extensive and addictive.
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    I have to SECOND THAT.

    If anyone wants to start up RBC-A Im here to help..and I need it.

    RBC-A = RomanBlack.Com Anonymous

    The PIC SMPS had me up ALL hours of many nights.. Its CRACK for EEs ;)
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    What design are you looking at in specific? Maybe we can help.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    You'll be hard-pressed to get a 555s' frequency drift below a couple percent of the output frequency. That's just the nature of the beast.

    As windoze killa inferred, a crystal oscillator will be several orders of magnitude more stable.
    Temperature compensated crystal oscillators (TCXO) improve on that.
    Oven controlled crystal oscillators (OCXO) are even more stable.
    If you need an even more stable oscillator, you'll have to go to rhodium, which can get expensive. Roman Black's OCXO is an excellent idea to accomplish very cheap and very stable; plenty stable enough for virtually anything a hobbyist might wish to build.
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    You can use a cheap microcontroller to achieve a much stable PWM.
     
  12. radiohead

    Active Member

    May 28, 2009
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  13. Artikbot

    Member

    Nov 7, 2010
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    Wow! So we can see we've seen our eternal 555s be surpassed by another circuit. According to the datasheet it seems as it is pretty much better than our fellow 555s.

    How's the pricing though?
     
  14. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    Its quite a response I have to admit, and theres some great ideas here.

    I'd rather use a pic chip to generate the PWM but while I know how to wire it all up, I don't have the experience necessary to actually program it. And lately time hasn't been forthcoming either, so learning assembly or c hasn't been an option.

    I think I'll just have to lean towards high quality components.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Why don't you tell us what you're trying to accomplish?

    There are many ways to skin the proverbial cat.
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    Which is what I said in post #9.

    I'm not too sure I'd claim the LM322 is superior. Different, but the core problem using RC timers is the resistor/capacitor, not the solid state parts.
     
  17. wires 1

    New Member

    Nov 21, 2014
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    Hi As a square wave astable I've been trying to stabilise the SE555D at around 20Hz for some time.
    I now use 3 x 0.22 COG (NPO) SMD caps, 2 x 20K fixed and 2 x 3K3 linear PTC thermistors.
    Pins 6 and 2 are connected together the resistor chain is to pin 3 and the caps to earth, pins 7 and 4 are not connected, pins 5 and 1 have a 0.1 COG (NPO) SMD cap across and pin 5 has a 0.1 COG (NPO) SMD cap to earth. I have a 1N4148WS in the power for reverse polarity protection.
    This configuration gives me 19.95Hz at ambient and 20.01Hz at 125 deg C. 0.05Hz over 100 deg C. Stable enough for my use and on a circuit board the size of a postage stamp.
     
  18. MrChips

    Moderator

    Oct 2, 2009
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    Please do not respond to threads many years old.
    If you want to start a new thread on the subject that is OK with me.

    If you wish me move your post just let me know.
     
  19. wires 1

    New Member

    Nov 21, 2014
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    Hi MrChips - I am unable to find where to start a new thread. Help!
     
  20. MrChips

    Moderator

    Oct 2, 2009
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    Click on Forums
    Select General Electronics Chat (or the suitable forum)
    Click on Post New Thread button at the top right of the page.
     
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