Identify a circuit.

[Lightium]

I've read that this is a multivibrator circuit, but how is it a multivibrator and what kind?

 

[rjenkinsgb]

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.

 

[Lightium]

I found this:

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

 

[Grossel]

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.

 

[Lightium]

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

 

[Grossel]

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

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

 

[Nigel Goodwin]

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

Square wave.

 

[Lightium]

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

 

[JimB]

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