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Make triangular wave using 555 timer

Discussion in 'General Electronics Discussion' started by spider_dula, Nov 18, 2011.

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  1. spider_dula

    spider_dula

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    0
    Nov 17, 2011
    Is there a direct way of getting a triangular waveform from a 555 timer.
    The method I know is to generate a square wave using the 555 timer and converting it to triangular waveform using an integrator or a low pass filter.

    But I just want to know if I can directly get a triangular wave from from the 555 timer just like how we get a square wave from it.
     
  2. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    There will be a triangular or perhaps sawtooth waveform on the capacitor in a 555 timer. Any loading of this signal will upset the oscillator, an integrator on the low impedance output would be preferred.
     
  3. davenn

    davenn Moderator

    13,948
    1,990
    Sep 5, 2009
    Yup thats true Duke :)

    hence an easier way is probably just to use a couple of op-amps like this cct.
    use a couple of 741's or say a dual opamp like a LM358

    [​IMG]


    The first Op-Amp is the oscillator, the second Op-Amp is the intergrator

    cheers
    Dave
     

    Attached Files:

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,501
    2,841
    Jan 21, 2010
    To directly get a triangular wave from a 555 you would need to monitor the charge on the capacitor.

    The problem is, this capacitor is charged by a resistor and hence the rate of charge decreases as the capacitor charges. This leads to a waveform that is not quite triangular.

    In order to get a straight line, the capacitor needs to be charged and discharged via a constant current source.

    Using a normal 555 oscilator circuit this isn't easily possible.

    One option is to use "constant current diodes" placed back to back (these are essentially jfets with the drain tied to the source) in the charge and discharge path. Again this is tricky with a normal 555 circuit, so I would opt for the variation where the output is used to control charging and discharging.

    As mentioned earlier the output is high impedance and would need to be buffered in most cases.

    In addition, because the current is programmed by the constant current devices, it is tricky to change the current. Thus changing the frequency is most easily done by changing the capacitor. Also the constant current diodes are often not tightly matched and their current will vary with temperature. Thus the exact rise and fall rate will vary (and with it, the frequency).

    This isn't a great solution, but it is one which uses (mostly) just a 555.

    Here is a circuit which uses a pair of variable constant current sources to do what you ask (but it's quite a bit more complex than just a 555).

    When I look at the various options, Davenn's solution is better than shoe-horning a 555 into something.
     
    Last edited: Nov 19, 2011
  5. erayurtseven

    erayurtseven

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    May 17, 2013
    triangular wave generator

    Hi,Davenn . Is your circuit suitable for high frequency ? About 10-20kHz
     
  6. BobK

    BobK

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    Jan 5, 2010
    That depends on the opamp you use.

    Bob
     
  7. erayurtseven

    erayurtseven

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    May 17, 2013
    lm358
     
  8. BobK

    BobK

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    Jan 5, 2010
    Should be alright at 20KHz.
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Hey Dave, I looked at your schematic, then your statement and thought .. "Shouldn't that be the first and second OpAmp forms the Osc but the second OpAmp alone forms the integrator"? ....Then I saw the positive feedback on OpAmp1 and thought .... "Gee! Sure glad I didn't post that"! :D :p

    Chris

    Edit: Hey after looking at it again 'C' is located in OpAmp2, I think I was right the first time! ;)
     
    Last edited: May 20, 2013
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