How does a simple oscillator work in non-ideal conditions?

Thread starter Tactified
Start date Sep 29, 2013
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Oscillator

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SUMMARY

This discussion focuses on the operation of a simple oscillator circuit involving PNP and NPN transistors, specifically in non-ideal conditions. The circuit utilizes a capacitor (C1) and resistors to create oscillation through positive feedback, despite the challenges posed by real-world components. Key insights include the role of the capacitor in charging and discharging, the behavior of the PNP transistor when current is applied to its base, and the importance of feedback in maintaining oscillation. The circuit's oscillation frequency can be influenced by component values, such as using a larger capacitor to achieve a slower oscillation rate.

PREREQUISITES

Understanding of basic transistor operation, specifically PNP and NPN transistors.
Familiarity with RC (resistor-capacitor) circuits and their charging/discharging behavior.
Knowledge of positive feedback mechanisms in electronic circuits.
Ability to interpret circuit diagrams and analyze current flow using Kirchhoff's Current Law (KCL).

NEXT STEPS

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Explore computer simulation tools for circuit analysis, such as LTspice or Multisim.
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USEFUL FOR

Electrical engineering students, hobbyists working with oscillators, and electronics enthusiasts seeking to deepen their understanding of transistor-based circuits and oscillation principles.

Oct 1, 2013

meBigGuy

Gold Member

I fully understand a bistable mult-vibrator like "oscillator" and was attempting to analyze with that in mind, especially since that was the description.
I had a problem with the off cycle.

" At this point there is not enough base current on Q1 to keep the collector of Q2 close to supply voltage. "

That's where I had a problem. My thoughts were that if R could supply enough current to turn on Q1, the current into Q1 Base would never drop enough to turn it off. I still have a small problem with that since it take very little current on Q1 to keep Q2 saturated. But, then again, it requires very little voltage change at Q2 to get Q1 fully off - maybe even noise is enough since gm is high.

The other thing I don't like is that the base of Q2 is open circuit when Q1 is off, meaning leakage current (Q2 Icb and Q1 Icb and Ice) will tend to keep it on a bit. Feels sloppy.

Looks like starving Q1 Ib with high R is what makes it work.