[Moved]: What is Purpose of this OP amp circuit??

[angy]

I was reviewing some circuits and this circuit got my attention .I was wondering what is the operation and its function ? It seems some sort of pulse generating circuit between 27V & 15 V . What will be the Time duration between the pulses.
Zener are 5.6V each

 

[ArticCynda]

Re: What is Purpose of this OP amp circuit??

This circuit is a bit too complex to determine its purpose "on sight", you'll have to simulate it.

 

[CataM]

Re: What is Purpose of this OP amp circuit??

OP amps usually have symmetric voltage supply, I mean , in your case the "+" have 27 V and the "-" pin why don't have -27 V?

 

[schmitt trigger]

Re: What is Purpose of this OP amp circuit??

By the pinout, this is a single device opamp packaged in an 8-pin package.

Therefore (pin7) is supply V+ and (pin4) is supply V-.

How come pin4 is not connected to ground directly, but rather through a 1k5 resistor?

 

[ydtech]

Re: What is Purpose of this OP amp circuit??

It probably works, but how well is another matter, there are some issues.

As it is, the zeners at the left make a reference voltage.

Suppose that the 100n is initially uncharged, then the - input is above the + input, and the output is low. This charges the capacitor through D1 and the 7k5. Once the capacitor is below the + input the output changes state, D1 blocks any current, so the capacitor discharges through the 680k. At the same time the resistor network around the + input makes it slightly higher than it was, creating some hysteresis.

When the capacitor is sufficiently discharged the output again changes state, pulling the + input slightly lower again. The circuit will output a rectangular wave between + 27 and 0 volts, approximately. The zener at the output seems to be for some kind of limiting the voltage swing.

I believe there are some drafting errors, the - supply lead should go to ground and not to the 1k5. For better symmetry insert another 1k5 at the top of the chain.

Better yet, toss the zeners and the 1k5's, the way they're set up makes little sense, and replace them with 10k resistors directly across the supply bypassed with some 10 uF.

No -27 V supply is needed, as the inputs are referenced to about 1/2 Vcc, and the output swings around that value, never going negative.

 

[Audioguru]

Many opamp circuits do not need a negative supply voltage.
Look at the many RC Oscillator Circuits in Google Images to see that this one is similar to many of them.

 

[barry]

Looks like some kind of oscillator. But that 1.5K resistor in the negative supply line is perplexing. I would definitely simulate this to see what it really does.

 

[betwixt]

It's certainly unusual but the resistor is just a supply dropper. The current through the two Zeners and the 1.5K will probably stabilize a ~11.2V supply across the IC, the odd thing is the whole output waveform is lifted by the voltage dropped across the 1.5K. Conventional design would move it to the positive supply and add a decoupling capacitor so the output was ground referenced. Perhaps the shift above ground is why the additional Zener at the output was added.

Brian.

 

[schmitt trigger]

You are correct that it may be a dropping resistor for the zener, but it is poor engineering practice not to include a decoupling cap to ground.

 

[goldsmith]

Hi

I think it's an oscillator , which is based on some sort of schmitt trigger circuit , and it's out put must be square wave , ( mixture between relaxating oscillator and schmitt trigger circuit , and i guess , it's D.C isn't 50 percent !
However there is some confusing things in that as "barry" said too !
Best Wishes
Goldsmith

 

[mtwieg]

The zener diodes are creating bias voltages for the circuit, including the op amp's supply pins. Not sure why. It would certainly be a lot easier to interpret if that mess was replaced with supply symbols.

It's definitely some sort of oscillator, but as it is I don't think it will work., at least not very well. When the output is high, the noninverting input will be very close to zero, but the diode in the negative feedback path will prevent the inverting input from being positive, so once the circuit is in that state it won't flip back.

I imagine that with real components it will probably oscillate, but not in a very well defined way.

 

[schmitt trigger]

Perhaps if the original poster would tell us where he found this circuit and where it is used, we wouldn't be taking wild guesses.

But the OP has unfortunately gone AWOL.

 

[crutschow]

A good example of a badly designed circuit.

 

[angy]

I am attaching file of the output signal at pin6 of op amp .Which components in the circuit controls the duration between two pulses ?

 

[FvM]

Take the circuit as is and change the capacitor value to scale the pulse period. Should be strictly proportional over a wide range.