How to make a triangle waveform

Discussion in 'The Projects Forum' started by andy24691, Nov 18, 2011.

  1. andy24691

    andy24691 Thread Starter Member

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    I have to generate a triangle wave at 200 kHz, would the circuit posted above be appropriate? I have an LM324N quad op-amp chip with a bandwidth of 1MHz, will this be sufficient? Also I don't understand what the voltage divider on the right of the diagram with the diodes is supposed to be? I'm guessing the other voltage divider is for generating the voltages necessary for the op-amps. Also I thought the triangle wave appears at the output of the integrator and not the input.

    cheers
  2. Audioguru

    Audioguru New Member

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    The output of a lousy old LM324 opamp has trouble above only 2kHz due to slew-rate limiting. Most half-decent opamps work well up to 100KHz but you need one that has a good output up to 2MHz.

    The voltage divider with the LEDs is connected to the output of the square-wave opamp and one LED lights when its output is high and the other LED lights when its output is low.
  3. sheldons

    sheldons Active Member

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    Heres a schematic you can feed with a square wave and get a triangle wave out......

    Attached Files:

  4. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    Welcome to AAC!

    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    This was split from

    http://forum.allaboutcircuits.com/showthread.php?t=60094

    The answer is the same as given to the other OP, you will need a much faster op amp to do what you want.
  5. andy24691

    andy24691 Thread Starter Member

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    Sorry I didn't realise.

    Referring to the schematic posted by sheldons, if you input a square wave of 200kHz into the circuit am I right in saying the output should be a triangle wave of 200kHz?

    I also don't know the difference between line and field rate?
  6. sheldons

    sheldons Active Member

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    Last edited: Nov 21, 2011
  7. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    It is a simple RC osciallator. The twist comes in the form of the integrator coming out with a linear wave form, the triangle wave. It is a close cousin of the 555 Hysteretic Oscillator, which uses a RC intigrator instead of an op amp version.

    If you need a linear ramp, and not a triangle you could use this design, which is much simplier.

    [​IMG]

    This from my cookbook, a work in progress stalled.

    My Cookbook

    Think about using an op amp integrator, the op amps have to be very fast. A LM324 would have trouble following your signal at unity gain, let alone creating it. Think in terms of a much faster op amp, something like a TL084 or better.

    High Speed Op Amp Query

    The reason a thread belongs to the person starting it (in this case you) is to prevent someone from confusing the issue and leaving you with no answer. Since this thread is yours you can take it whatever direction you want, generally understanding a circuit isn't linear for people, and there is no telling which explination will click best for you.

    I'm not sure which schematic you were referring to, but I suspect it is an old project of mine that resembled a function generator (loosely). It made a square wave, triangle wave, and a rough approximation of a sine wave.

    I tend to draw a lot of schematics, some of them are even useful. :D
    Last edited: Nov 21, 2011
  8. andy24691

    andy24691 Thread Starter Member

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    I was considering the circuit you posted on the thread that I "hijacked"

    http://forum.allaboutcircuits.com/showthread.php?t=60094

    I was confused because I thought the triangle wave should be at node B following the integrator instead of node C. How will I know which value components I'll need, I also decided 300kHz would probably be better for my purposes :D
  9. Bill_Marsden

    Bill_Marsden Moderator Staff Member

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    That gets harder, though I'm sure there are parts that can do it.

    Part of the problem is phase, the integrator has to be inverting, which means the 555 section needs not to be. The 555 sets the amplitude of the wave form because of it's 1/3 and 2/3Vcc setpoints as a Schmitt Trigger.

    BTW, you do want a symetrical triangle wave form?
    Last edited: Nov 21, 2011
  10. andy24691

    andy24691 Thread Starter Member

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    Yes, its for PWM of an audio signal as part of a class D amplifier
  11. Audioguru

    Audioguru New Member

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    Node B and node C both produce triangle waves.
    The pin2 and pin 6 inputs of the 555 needs node B to be inverted so the second opamp is a linear inverter.

    Attached Files:

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