modified 6 years ago

Meissner Oscillator

A Meissner Oscillator or sometimes (especially in USA) refered more as an Armstrong oscillator is a very peculiar type of oscillator. Almost every other type of oscillator relies on some sort of galvanic feedback, directly from output to input, while this oscillator completely separates the input from the output via a small transformer. The windings are placed in antiphase so that the returned signal is 180 degrees phase shifted and the transistor gives you another 180 degrees feedback, because it's in a common emitter topology totalling in a 360 degrees full positive feedback. The 47k resistors set the bias, along with the 100k resistor which also acts as an AC level limiter, somewhat limiting the total signal in the positive feedback, which enables you to fine adjust for cleanest output. You can further vary the gain, and the oscillations with the 6.8k resistor which makes it handy when switching loads. The 1k resistor is an emitter degeneration negative feedback further reducing hard clipping and improving stability and the oscillation frequency is determined by the resonance frequency of the tank circuit. Some of you may find some similarities with a joule thief, and they'd be 100% correct because the only difference between the two is that in a joule thief the amount of positive feedback is almost not controlled at all. The feedback slashesh the output very vigorously into cutoff and we all know what happens when you abruptly cut the power supply to an inductor. It creates a voltage spike of its own, to dump the excess current, before the magnetic field collapses. Well here the process is controlled before it gets out of hand, resulting in a very pretty sinewave oscillation :D
published 6 years ago
6 years ago
The blocking oscillator is a similar circuit that generates pulse and ramp waveforms. Most joule theif circuts are blocking oscillators at heart.
6 years ago
Nice circuit and description btw.
6 years ago
A joule thief and a blocking oscillator and a meissner oscillator for that matter are all one and the same. The difference is that a Meissner Oscillator has a more well controlled feedback than the others
6 years ago
4 months ago
How do you calculate the frequency of this circuit, is it determined by base resistor? What formula would I use to calculate?

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