how to solve and understand this opamp circuit

[haseeb zaib]

hello everyone

The circuit which u are seeing here is a part of PI metal detector. I am really confused what this part is actually doing and in what configuration is this circuit working in. Let me give a brief explanation. There are two signals coming into the inverting input of opamp whose peak voltage is 5v, then there is this switch and transistor part, the delay signal which is operating the switch has "ON" time of 50uS, And there is 5.3-5.4V on base of transistor. The value capacitor on feedback is 100nF. Can someone explain me what this part in general is doing and how can i understand or solve it ?


Thanks

[surfdetector]

It would be nice to see the whole schematic.

[kt315]

It would be nice to see the whole schematic.

The Delta Pulse. believe me.

[green]

Don't know what the circuit would be used for. U13C tries to keep voltage at pin9 same as pin10(6V). With switch open, circuit is an integrator. Switch closed a low pass filter. Q6 turns on when the U13C output goes low around 4.7V so output doesn't go below about 4.5V if switch is closed.

[kt315]

Don't know what the circuit would be used for
--
ok. a circuit.

[green]

Don't know what the circuit would be used for
--
ok. a circuit.

Thanks for the schematic. Appears to be the integrator. More going on than the integrator I use. Need to study it more to determine the advantages if any.

[Carl-NC]

It's a sampling integrator. Usually we put a resistor in parallel with the cap for stability, in this case the resistor is switched in during one of the sample cycles.

The transistor appears to be a limiter. If the output falls below 0V (assumed during the sample cycle) then the transistor pulls current through the input R and keeps the output close to ground.

[green]

It's a sampling integrator. Usually we put a resistor in parallel with the cap for stability, in this case the resistor is switched in during one of the sample cycles.

The transistor appears to be a limiter. If the output falls below 0V (assumed during the sample cycle) then the transistor pulls current through the input R and keeps the output close to ground.

I'm thinking the added switch was needed to reduce output ripple due to pulsing at a low rate, 100 or 120pps. Any other reason to add the switch?

[kt315]

Any other reason to add the switch?
---
in this case the resistor is switched in during one of the sample cycles.
----
just in during FIRST SAMPLE time. then, this circuit will be prepared to next cycle, of 'summation'.
anotherway you have to look all schematic in complex.

[Carl-NC]

I'm thinking the added switch was needed to reduce output ripple due to pulsing at a low rate, 100 or 120pps. Any other reason to add the switch?

That would be my guess.

[kt315]

I'm thinking the added switch was needed to reduce output ripple due to pulsing at a low rate, 100 or 120pps. Any other reason to add the switch?

any part of the sch serves just to better stability because the Delta Pulse is static, non motion, concept.

[Carl-NC]

any part of the sch serves just to better stability because the Delta Pulse is static, non motion, concept.

Another good reason.

[sirbedevir]

17 years later...
perhaps the original circuit of Delta Pulse using other op amp then TL062, and was need to limit the next stage op amp input below 0.7V?

[kt315]

nobody saw original sch. there was just one file with Orcad made circuit from one bulgarian and a sketch from second bulgarian.
no info more was got from both. also, no detail info on data of original coils. absent.

[Riss]

About 20 years ago , this scheme – Sniffer XR71 made me very angry . We worked together with a friend in the field with this detector . On the second day i installed two 1N4148 and a 47k resistor in a diode "OR" scheme in pin6 on 4066 , so that it can also be closed during the second sample (delay approx. 300- 700 microseconds ) . The detector started working better . But the autotune operation with a time constant of about 15 seconds made me angry and I installed a switch with which I turned it off after the "pop" started (we always worked on slow popcorn ,where my friend's job is to keep the frame on his side about 15cm above the ground , and I changed the height of my side of the frame slightly and in this way ,,autotrack’’ was done - I compensated for the slow change of the soil effect . Those were glorious times- we dug up so much iron -enough to build a railway bridge over the river Danube .