100 khz triangle wave generator..

Discussion in 'The Projects Forum' started by baggio2, Jan 2, 2009.

  1. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    hi...i wanna generate 100 khz triangle wave and designed that circuit by using TL082 opamp . it works in simulation program but not in real..what is the problem?am i using wrong opamp? which opamp should i use if TL082 is wrong?
     
    Last edited: Jan 2, 2009
  2. SgtWookie

    Expert

    Jul 17, 2007
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    I don't see how it worked; you don't have any Vcc or Vee supply to the opamp.

    R5 is too low in value. I received a very distorted and clipped triangle wave when I simulated your circuit. Increase it to around 2k.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I tried something similar. I need to look a little closer. Let me study it and I'll get back with you. Meanwhile, you can take a look at my experiences, it didn't go too smoothly for me either at first, but I did figure it out.

    http://forum.allaboutcircuits.com/showthread.php?t=12405

    The 555 makes a nice Schmitt Trigger, which is half of what you've built. Yours is noninverting, which is good. What I need to calculate is the hysterisis voltages, this will determine what the amplitude of the triangle will be. What are your power supply voltages? Gee, I think Wookie said something similar...

    R5 is 470Ω, and C3 is 0.4µF, correct? The others are 11KΩ and 10KΩ?
     
    Last edited: Jan 3, 2009
  4. DickCappels

    Moderator

    Aug 21, 2008
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    If it works with a much larger capacitor as C3 (much lower frequency), then suspect the opamp. The unity gain bandwidth of an TL082 is only 3 MHz.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Just a quick redraw, to allow for easier readablility (and as a check).

    [​IMG]

    I'm looking at hysterisis, I suspect it is way too wide. If the power supply is ±12VDC and the output is +12V, then it will take at least negative 10.9V to make it switch. It works this way for the other polarity too. This assumes the op amp can go rail to rail, a dubious proposition. Try reducing R7 to 4.7KΩ and see how it works.
     
    Last edited: Jan 3, 2009
  6. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    the most important thing in this circuit is frequency...i need 100 khz and i am using TL082...this opamp is enough for my circuit?? your circuit is 3 khz...
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    In your simulation circuit you are using a dual power supply arrangement. Are you using a dual supply to power the real thing? If not then the circuit as drawn will not work.

    hgmjr
     
  8. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    yes i am using dual supply in real...+9 and -9 volt for opamp...
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Is your dual supply a benchtop supply, or 9v "transistor" batteries?
     
  10. Wendy

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    Mar 24, 2008
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    So what are the real part values? Your diagram wasn't very clear, which is why I tried to redraw your schematic. You do need to drop R7, the good news is you get to use larger parts on C3/R5 to compensate.
     
  11. SgtWookie

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    Jul 17, 2007
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    I'm willing to bet that he's trying to use 9v transistor batteries without 100nF transient surpression caps between his Vcc/Vee pins and to ground.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Your triangle gen. is duplicate , except for some values, of AN20-10, National Semi. Application Hand book 1.1973. It shows R5 as 1.4k in series with 140k pot,for frequency control,R6 10k with 1M pot for amplitude.For 100k Hz C3 about 1.6 nF,@ R5 1k.
     
  13. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    ok i am gonna post full schematic...its frequency is 138 Khz according to
    the formula and it is enough for me but doesnt work in real...is the problem TL082 or something else...? and my dual supply is a benchtop supply...
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    I'm still curious as to what the parts are. For example, C1 is 4n7. What is that?

    You're new hysterisis trigger point is 6.71V of 9V. That is 75%, which is better than the 91% trigger point.

    Look at your voltages, the Schmitt Trigger is easy to tell if it is working or not. The other op amps should have the same voltage on both the inputs.

    [​IMG]
     
    Last edited: Jan 3, 2009
  15. hgmjr

    Moderator

    Jan 28, 2005
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    Bill,

    4n7 is just another way of expressing 4.7 nanofarads.

    However there is a bit of inconsistency since the 8.2 kilohm resistor should be written 8k2 if the convention is to be maintained.

    hgmjr
     
  16. Wendy

    Moderator

    Mar 24, 2008
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    OK, so here is the updated schmatic.

    [​IMG]
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    The opamp has a difficult time trying to drive R5 when it is as low as 470 ohms. The opamp will clip which distorts the waveform. Use a minimum of 2.2k for R5 and reduce the value of the capacitor to get the frequency back to 100kHz.

    The TL081 has a voltage gain of only 30 at 100khz so the triangle-wave will be curved a little.
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    Yep, that's the basically the same track I started off with. Our OP was so slow in responding that I thought he was gone.

    I simulated it using an LF353 model, which is the same as TI publishes for the TL082 and TL072. With a few mods, it looks pretty decent at 110kHz.

    Simulation attached.
     
  19. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    so will ur circuit work in real? becos my circuit is working in simulation too...anyway i better try it...thank you for ur help..
     
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