Identify a circuit.

rjenkinsgb

Well-Known Member

Most Helpful Member

• Jun 26, 2022

• #2

It looks to be a schmitt trigger type oscillator.

A similar concept to this one, where the input threshold is changed as the output switches high or low, and the capacitor has to charge or discharge past that threshold point each way for the output to switch to the opposite state.

 

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Lightium

Active Member

• Jun 26, 2022

• #3

I found this:

https://www.researchgate.net/publication/258686230_DC_operating_points_of_transistor_circuits#pf7

 

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Grossel

Well-Known Member

• Jun 27, 2022

• #4

The circuit can be viewed as a very crude op-amp variant. I borrowed both images just to give an idea how or why it can be viewed as an opamp.

 

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Lightium

Active Member

• Jun 27, 2022

• #5

Grossel, should I be getting a square wave or sine wave on R8?

 

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Grossel

Well-Known Member

• Jun 27, 2022

• #6

Lightium said:

Grossel, should I be getting a square wave or sine wave on R8?

Click to expand...

I'd expect neither. Unfortunately I don't happens to have a simulator software installed, but somebody else in here probably has, to provide an exact answer. Schmitt trigger, of course it should be expected square wave

 

Last edited: Jun 27, 2022

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Nigel Goodwin

Super Moderator

Most Helpful Member

• Jun 27, 2022

• #7

Lightium said:

Grossel, should I be getting a square wave or sine wave on R8?

Click to expand...

Square wave.

 

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Lightium

Active Member

• Jun 27, 2022

• #8

I am in the middle of reading this:

Transistor Schmitt Trigger Oscillator

The Schmitt Trigger oscillator below employs 3 transistors, 6 resistors and a capacitor to generate a square waveform. Pulse waveforms can b...

saima-elec.blogspot.com

 

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JimB

Super Moderator

Most Helpful Member

• Jun 27, 2022

• #9

Some months ago, I had the task of analysing this circuit:

As you can see it is a very close relation to the circuit in post #2.

It is a slow oscillator producing short pulses of 0.6s duration, every 5.8s.
This asymmetric waveform is due to D1 and R3 in parallel with R4.

I expect the waveform of the circuit in post #2 to have a 50/50 mark space ratio.


Here are the waveforms at the op-amp inputs, the output of the op-amp is a square wave.








Enjoy.

JimB

 

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