Op-amp Saw tooth generator

Discussion in 'The Projects Forum' started by cougle, May 6, 2013.

  1. cougle

    Thread Starter New Member

    Mar 19, 2013
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    I needed a circuit with op-amps for saw tooth waveform generation, I came through the following circuit and modified it according to my requirements.The circuit worked fine in simulation, but practically when I mounted It gave a triangular instead of saw tooth waveform ,and frequency was a little less

    I tried playing with resistance R1 that could make it more saw tooth insead of triangular by reducing it, and with resistance R2 increasing it. But reducing it resulted in distorted waveform and increasing R1 increased the frequency and made it more triangular whereas. Changing R2 didn't had much significant of an effect.What could be the problem?
     
  2. cougle

    Thread Starter New Member

    Mar 19, 2013
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    I forgot to attach the circuit here it is, The First LF353 is used in comparator configuration and second as opamp integrator.
     
  3. cougle

    Thread Starter New Member

    Mar 19, 2013
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    I checked with slew rate requirement it was within ICs tolerance
     
  4. Matter45

    New Member

    Dec 13, 2012
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    10nf is tiny! ever wonder what happens to a 10uf capacitor when you fully charge it then attach your probes to the terminals? it discharges! now imagine this with a 10nf capacitor!
     
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  5. cougle

    Thread Starter New Member

    Mar 19, 2013
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    But I am having the problem that discharge time doesn't get smaller !It remains equal and what I get is a triangular waveform.
    The discharge and charge time remain equal even with the resistor ratio 20k/1k charging Discharging respectively

    The frequency of circuit changes with changing resistances but the duty cycle doesn't!
     
  6. Matter45

    New Member

    Dec 13, 2012
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    just a question, why do you have both Vcc positive and negetive pins to a positive charge on the schematic? To my knowledge, one side needs to be -5v, and the other +5V.

    Edit: for example. have two 5v batteries in series. declare the node between the two batteries in series as ground. connect the negative side of the battery pack to the -Vcc and the postitive to the +Vcc.

    Your schematic should have one of the positive side of the 5v power supply pins connected to ground, and the negative side connected to -Vcc on the Op Amp. Looking up LM353....
     
    Last edited: May 9, 2013
  7. Matter45

    New Member

    Dec 13, 2012
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    most of the datasheets I come across for LM353 is for a Duel Op Amp. please either provide the datasheet for the LM353 that u are using or redo your schematic to reflect the duel Op Amp IC.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Look closer. There are two +5V and two -5V batteries.
     
  9. cougle

    Thread Starter New Member

    Mar 19, 2013
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    I have edited the value -5V dc and used the +ve terminal . triangular waveform was appearing
     
  10. cougle

    Thread Starter New Member

    Mar 19, 2013
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    It is LF353 and yes its a dual op-amp in one Ic.This is for simulations , and as there is no built in pscpice model for LF353 so I made it and it is appearing as. The circuit is done with both opamps beng used in one IC.
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I'm not sure what you mean.
    Do you still have the same problem? I can't see any reason for it, unless your diodes are both shorted.
     
  12. Matter45

    New Member

    Dec 13, 2012
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    whats with that lonley R4 resistor?

    Can i suggest to lower R3 to 200k and increase your capacitor to 10uf for diagnostic purposes. Should decrease the frequenzy.

    Also if you swap R1 and R2 you should get the opposite direction of the sawtooth? currently you have positive as the discharge cycle with that schematic.
     
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