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    • #10787
      LectronFan
      Moderator

      Hi all,

      The simpliest sawtooth oscillator can be build with only a handful of Lectron modules.

      Here is setup picture where I use the oscilloscope to monitor the waveform.

      Sawtooth oscillator

      Here’s a short circuit description.

      The NPN and PNP transistor form a so called thyristor.

      The base of the PNP transistor has a fixed setting with the voltage divider of the 220 Ω and 2,2k Ω resistors.

      The 0,1μF capacitor charges via the 250k Ω potentiometer and 100k Ω resistor.

      When its charge voltage is high enough, the PNP transistor conducts and the capacitor quickly discharges through the C-E junction of the PNP and B-E junction of the NPN transistor.

      Now this process repeats and the result is a sawtooth.

      Many greetings

    • #10788
      Michael
      Keymaster

      Very nice Frank!  Square wave generator next?

      What is the typical application for a sawtooth oscillator in electronics?

      Fellow Lectroneers should note that this circuit uses a NEGATIVE ground rather than what the legacy Lectron System circuits use which is a positive ground.

      Best regards to all,
      Michael

      • This reply was modified 3 months, 2 weeks ago by Michael.
      • This reply was modified 3 months, 2 weeks ago by Michael.
    • #10806
      LectronFan
      Moderator

      Hi Michael,

      The sawtooth oscillator is often used nowadays as tone generator for musical instruments.

      It might also be used to make a PWM oscillator.

      Since the sawtooth oscillator has many functions, we will make some experiments with it.

      I will give examples of that layer on.

      Although our little circuits works nicely, it has some drawbacks. The amplitude is small since we are using the very steep charging time of a capacitor.

      Remember that the charging curve of a capacitor is parabolic. I explained this a while ago in another project.

      The next disadvantage is that the sawtooth waveform is not quite lineair.

      If we would replace the 0,1μF capacitor with a 10μF capacitor, just like in the next setup picture, the oscilloscope shows these artefacts. You clearly see how the slope is not lineair. This is because the capacitor is larger in value and the charging time is different.

      Later I will propose here a solution for this problem. No matter which capacitor value we take, the slope will be perfect lineair.

      Till later.

      Sawtooth not lineair

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