PrathikP

modified 6 years ago

A working Hartley Oscillator

318

04:49:16

SHAKE TO START!
The solution to make it oscillate is simple: just add a small resistor to the output of the op amp. This is done because the otherwise low output impedance of an op amp apparently prevents a phase shift and hence prevents oscillations.

published 6 years ago

fatcat2

6 years ago

Why doesn't adding a resistor with the inductor work? What gain should be chosen so that there is no clipping?

fatcat2

6 years ago

Adding 2 zeners and a pot works but the THD is very much degraded.

PrathikP

6 years ago

And why would you add a zener diode? There is absolutely no point of that.

PrathikP

6 years ago

The resistors added to the inductors is different from the resistor added to the output of the op amp

PrathikP

6 years ago

The inductor resistors are used because EC inductor has no resistor, because of which simulation errors occur. The reason for adding the op amp output resistor is in the discription

PrathikP

6 years ago

And the gain has to be selected by experimentation. You gain must be high enough to sustain oscillations, but not so high that clipping occurs

fatcat2

6 years ago

👉http://everycircuit.com/circuit/6169343656984576

fatcat2

6 years ago

Thank you.

PrathikP

6 years ago

Presumably the output is distorted due to the presence of non-linear elements in your circuit.

fatcat2

6 years ago

Yeah! Which is better; a distorted waveform or a clipped waveform? (whose THD is less?)

PrathikP

6 years ago

Clipping can be avoided easily by adjusting the gain; as for THD, probably a non-linearly distorted waveform has worse THD?

fatcat2

6 years ago

But I can't find any resource which states the "right gain". Every book says that the gain should be greater than the attenuation but they're not considering clipping. I also think that a distorted waveform has higher THD.

kiani

6 years ago

æPrathikP that makes sense, thanks for post.

PrathikP

6 years ago

The "right gain" doesn't have a formula. It is not even a constant. You need to use a 10-turn pot in order to find the right amount of gain that just allows the signal rail-to-rail voltage swing without clipping

fatcat2

6 years ago

It is around It is around 1.04V/V. Thanks. This is not the same for all. Moreover, I found out that oscillation is very difficult to happen when L is lesser than 10*C...

billoute720

6 years ago

Oscillations are appearing a very short time (less than 1 ms). Just adjust the time base to see

PrathikP

6 years ago

If you increase the timebase @bill, the oscillations die due to various simulation calculation related reasons. The timebase is set low for a reason.....

fatcat2

6 years ago

So what to do for automatic gain control? The zener idea is obviously bad. There are various opamp ideas but that take twice the space of the oscillator itself. One thing to note is that high gain BJT CE amps woeks just fine without clipping. Why is that so?

fatcat2

6 years ago

But the problem is miller effect, which is very annoying. Sometimes, I use an AC coupled inductor to minimize miller effect by resonance.

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