EveryCircuit - RLC Op-Amp Oscillator

rich11292000

7 years ago

Opamp has internal power supply not shown

7 years ago

I see, thanks.

7 years ago

Fine, this is the correct first question, if you get an oscillator design and asked for "is this an working oscillator?" If you are really happy with the answere from rich you can go to next preconditions.

tjt263

7 years ago

@hurz Come again?

Markkus92

7 years ago

Ignore him

hurz

7 years ago

Go to the next precondition. Or better said, what is the logic behind "we need power to drive an oscillator"? @Markkus92, an idea, or just trolling?

tjt263

7 years ago

The first laws of motion & thermodynamics?

hurz

7 years ago

Right, an OpAmp is an active componemt and will help us to overcome that.

hurz

7 years ago

What we can see, its an LC oscillator and for a first guess we can calculate its working target frequency, right?

hurz

7 years ago

f resonance = 1/(sqrt(L * C) * 2 * PI) = 1592Hz

hurz

7 years ago

Suppose the oscillator is working and stable and will give us exact 1Vpp @ 1592Hz, how much and how does it is phase related we get a OpAmp input back?

hurz

7 years ago

Lets see, remove the opamp and see how much we get from out feedback network http://everycircuit.com/circuit/6127218523897856

hurz

7 years ago

From amplitude we get almost everything back in power. Only a little losses. 1 Ohm resistor, some magnetic losses in reality and some rounding losses here in simulataion. We just need to add a little gain to keep the oscillator working. A little gain 1+ let us start with 2V/V

hurz

7 years ago

But stop. Lets think about a third precondition. The total sum of loop phase! It MUST be Zero or Modulo 360°! In our case its Zero.

hurz

7 years ago

Now that after all preconditions are given lets see how it works. Shake to start http://everycircuit.com/circuit/6453796764123136

hurz

7 years ago

@Markkus92, are you still there?

tjt263

7 years ago

@hurz, sorry I've gone and messed with the values in the meantime. I appreciate your correspondence, but I'm having a hard time understanding you a lot of the time.

hurz

7 years ago

And im not finished 😁 lets wait for Markkus92 and see what he is contributing.

tjt263

7 years ago

He's gone.

anandranjith

7 years ago

Broo..that is some explanation...i cant even digest everything u just said..

romer37rus

7 years ago

shake the phone

hurz

7 years ago

@tjt263, why dont you take the original values from my circuit? 10uF, 1mH, 500us/s ...

csimpi

7 years ago

Opamp has 2 more legs connected to v+ and v- not shown here so there is power supply. Shake phone adds noise and starts it.

hurz

7 years ago

Anybody who follows this discussion is welcome. As more you read, as much you can comment without looking to stupid. The topic power supply was quickly clarified by @rich. If you think this needs more clarification then we can go ten steps back for you?!

hurz

7 years ago

@tjt263, you have also changed the original question you have. Why?? Dont you see that all comments now are completely usless? If you have a new topic, just open a new thread. Thanx.

hurz

7 years ago

@tjt263, also gone?

hurz

7 years ago

Anyway, continue with new LC values. What else needs to be taken into account if we would like to breadboard this type of oscillator? OpAmp are not sold with 2V/V open loop gain. They are available with gain factors like 1000, 10000, 1000000 or even above 1million. Manufactures do not specify this open loop gain exactly, they just give it as range in specification. Lets assume we have an OpAmp with 100000 with an additional feedback network beside LC we can tune the gain of 2 we need. http://everycircuit.com/circuit/5887198382784512

tjt263

7 years ago

@hurz Sorry, I don't get notifications when people comment. I just read this.

hurz

7 years ago

I also don't get notifications about your return!