modified 11 years ago

Help LC oscillator

02:52:23

I took the this LC oscillator from the examples, and I simply changed the simulation speed. What I noticed is that both voltage and current amplitude decrease as the time goes by. Try to flip the switch and you will see. Can anybody explain me why; I didn't expect this behaviour from this circuit.

published 11 years ago

mewyn

11 years ago

The simulation is taking into account system losses. You can never have a perfect system where this oscillates forever because all components have some degree of energy loss to them.

bartoo

11 years ago

Thanks mewyn. Is there a place where I can find more about these losses (their amounts) that every circuit introduces?

Mamish

11 years ago

I think it's more to do with simulation inaccuracies. After all, these are meant to be ideal circuits, and an ideal LC would last forever. I you change the sim speed the rate of amplitude change goes with it (it goes disproportionately short or long compared to the change in sim speed), which leads me to think it's a consequence of too many periods on too slow a speed.

nwfenton

11 years ago

The curve doesn't look like a simulation error, but rather it looks like exponential decay due to simulated ohmic loss. The device models probably have a built in resistance to make the calculations work...

bartoo

11 years ago

Good point. I agree with nwfenton.

Mamish

11 years ago

It's the dependence of the decay on sim speed that has me convinced. If you use 10ms/s the waveform is severely decayed after about 20 periods, but on 1ms/s there's almost no loss at all after 100. Worth noting too that EC usually does ideal components. E.g. inductors without series resistors sometimes make circuits fail since the simulator considers it a short at startup.

bartoo

11 years ago

I tried what you said, Mamish. And, indeed, it's true. The rate of the dacay seems dependent on the speed of the simulation. At this point, I really don't know what to think. The question stays open.

Igor

11 years ago

EC has ideal L and C. Oscillation is damped because of the used numerical method. There is more damping with larger time step. So use smaller simulation speed for higher accuracy.

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