thebugger

modified 3 years ago

Sawtooth Oscillator

289

06:28:19

I was thinking of substituting the PNP transistor directly with a diode from the cap to the output of the op amp to discharge the cap, but the simulation breaks up like that, so here's another angle of it. 

published 7 years ago

lenzrulz

7 years ago

Very innovative, well done!

thebugger

7 years ago

I'd like to try it with the diode replacement in reality to see if it'll work.

hurz

7 years ago

Lenny, you have no idea how this works. No need to be a bootlicker.

PrathikP

7 years ago

This is really nice. What exactly do you want to do with a diode?

Robert_Kidd

7 years ago

@hurz, so determined to show your idiot side. Why not just stay quiet!!

thebugger

7 years ago

I want to use the diode to discharge the cap instead of the PNP transistor

thebugger

7 years ago

But the simulation doesn't like that. Wonder if it'll work in reality, or the op amp will overshoot the discharge.

hurz

7 years ago

@thebugger, as long the peak current to discharge the cap does not hurt the OpAmp output or the diode itself, it will work in real. Right Lenny?

thebugger

7 years ago

@Hurz, that was my primary concern, but according to the simulation (which should not be trusted entirely), the discharge current is only a few mA which shouldn't damage any op amp. My other concern is the slew rate of the op amp. That is, at what maximum frequency can an op amp change the output state fast enough, to pull the capacitor voltage low. A TL071 should work up to 50-60kHz I think.

hurz

7 years ago

Lenny you agree? The edge will be endless and visible. Put together with a normal diode a 1kOhm resistor or lower it to 500 Ohm and see how slow this edge comes down. Anyway, it's fast enough to call it "sawtooth" Lenny might agree with his innovative knowledge.

hurz

7 years ago

Here a Lennyvotive version http://everycircuit.com/circuit/4770541509279744 Precharged capacitor to 5.3V close to the upper threshold 5.33V and start simulation to see even harmonics above 1.5MHz!!!!! Lenny just ask if you don't understand what @thebugger or I talking. You do not need to die stupid as fraudster.

thebugger

7 years ago

Hurz give him a break, he'll learn. Anyway, I'll give this a go at home with TL071 and a variable capacitor I have from 200pF to 1.2nF and see how it goes, with the diode version. Any ideas before I solder everything down.

thebugger

7 years ago

For instance, should I use some resistance to dampen the diode, if the op amp should overshoot?

maxmax_66

7 years ago

@lenzrulz. http://everycircuit.com/circuit/5023033101385728 what rebuttal? More like petty.

jason9

7 years ago

Hmm, seems to me like an inverted Schmitt trigger oscillator with a slow constant-current rise and a very, very fast drop.

lenzrulz

7 years ago

@maxmax_66...Petty? No, more like subjectivity, the rebuttal is in the detail, luckly someone's paying attention or they will be shortly...lol

thebugger

7 years ago

@Jason9 that's exactly how it works. A hysteresis sets two thresholds of operation and when one on them is reached the diode discharges the cap instantaneously (sort of) to the other threshold, where it starts charging up slowly again. That's always been the purpose of an op amp - to do anything possible to keep the two terminal voltages always close to each other. So it struggles to pull the negative terminal down to the second threshold and then disables. When disabled, the cap starts charging again.

hurz

7 years ago

Only one guy cant stop being a Troll a fraudster and a bootlicker. Start a discussion like we have with @thebugger's circuit.

Robert_Kidd

7 years ago

Most of your comments are snide and nothing to do with electronics.

hurz

7 years ago

The break is over, and the Bootlicker is so silent, no comments on electronics? Just here as season greeting clown?

hurz

7 years ago

@thebugger, everything what's looks like a shootover is caused of everycircuit simulation granularity or in other words by subsampling. Simulate slow enough and you do not see overshoots! Only Lenny shoots over its innovative ideas which he don't understand.

thebugger

7 years ago

Yeah, EC doesn't handle sawtooth too well, but still in reality an op amp may overshoot as well.

hurz

7 years ago

But not with that much feedback

thebugger

7 years ago

Yeah, suppose so.

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