# OP07 circuit output voltage?

1. ## OP07 circuit output voltage?

Hello All,

I need to know what voltage I should expect at output point X if both inputs were close to zero in the attached circuit?

Also please comment about the gain of the OP07 and the voltage at the output X if voltage between pin 2 and 3 of the OP07 is:

0.001 v
0.01 v
0.1 v
5 v

2. ## Re: OP07 circuit output voltage?

Without knowledge about an external feedback circuit, you can expect any voltage between -0.7 V and positive OP07 output saturation.

Any positive voltage difference between inv. and ninv. input larger than maximum offset will cause negative output saturation, in this case -0.7 V due to clamping diode.

3. ## Re: OP07 circuit output voltage?

At the moment I am getting 14 V. It should be 2.75 V according to the circuit documents. As you can see voltage at the R2 and R3 inputs are about zero. There is something wrong which causing this 14 V instead of 2.75 V. I am trying to find this problem.

Do you have any advice for the next measurement in order to find the faulty part?

I am thinking about connecting an oscilloscope between pin 2 and 3 of the OP07 and see what is the exact voltage between inv. and ninv. inputs? It is very difficult to do measurements because board is located inside a hard to reach place that is why I have to do more analysis that measuring. Parts are very tiny and any mistake can cause a big trouble.

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4. ## Re: OP07 circuit output voltage?

Hi,

At the moment I am getting 14 V. It should be 2.75 V
Because of the high gain and the input offset of the Opamp you will not be able to see significant change in input voltage when the output is 14V or 2.75V.

Klaus

5. ## Re: OP07 circuit output voltage?

At the moment I am getting 14 V. It should be 2.75 V according to the circuit documents. As you can see voltage at the R2 and R3 inputs are about zero. There is something wrong which causing this 14 V instead of 2.75 V.
Why 2.75 V? Why not 5V or 0V? Do you have additional information not yet revealed in the thread? Again, the voltage is undetermined without additional circuit elements.

6. ## Re: OP07 circuit output voltage?

2.75 is starting point. When circuit starts this voltage is supposed to be stabilized at 2.75 automatically. Then manually condition could be adjusted. input at R1 is the set value for the manual adjustment and inpout at R2 is the actual parameter value. Depending on the manual adjustments this voltage should be change and stabilize between 2.75-7 volts.

7. ## Re: OP07 circuit output voltage?

That's a completely useless description without showing the circuit which provides the respective function. The shown circuit is DC-wise open loop and doesn't stabilize anything.

8. ## Re: OP07 circuit output voltage?

the leakage in the caps and diodes determines Vo in the present ckt - which is very incomplete ...

9. ## Re: OP07 circuit output voltage?

@ FvM

You are right. I haven't include the whole circuit because close loop control has not started yet at this stage. There is an "On" button (not presented here) which by pushing it R1 and R2 will have real values and closed loop control will start and from point X regulating signal will go into another board which is a part of the closed loop. Above circuit is only showing pre-start-of-closed-loop-control condition. According to the circuit documents at this pre-start-of-closed-loop-control we should have 2.75 v at point X but we have 14 v inatead.

Main problem is the closed loop control overshoots like crazy and I am trying to find the reason and fix it. After inspecting I found the only mismatch from the documents is this voltage at point X. There are 24 other test pins which all are OK and match with the circuit documents. The only difference is this pin at point X. Voltage at this pin before starting closed look control should be 2.75 v according to the documents but it is 14 v. That is why I though overshoot of the closed loop circuit should be related to this pin which does not have the proper value. After fixing this and having 2.75 v at this X point I am expecting stabilized control without overshoot.

I measured voltages of pin 2 and pin 3 with respect to ground. Pin 2 = 0.032 v and Pin 3 = 0.1 v. Pin 2 to Pin 3 = -0.07 v. According to documents pin 2 and 3 should change between 0-4 v and point X should change between 2.75-7 v. Pin X never should go beyond 7 v during closed loop control. The whole complete schematics is about 37 A4 pages because there are a lot of another stuff added. that is why I couldn't put them all here and I just put the relevant part of the schematics.

With the above explanation please advice how to proceed for the next step?

10. ## Re: OP07 circuit output voltage?

Even the so-called "prestart" condition surely depends on some kind of external feedback or time discrete control mechanism. OP07 has typically 112 dB open loop gain, the input voltage must be set to the sub µV to achieve a specific output voltage like "2.75 V".

You did not yet post the relevant circuit parts.

First step is to understand how the whole circuit works.

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11. ## Re: OP07 circuit output voltage?

With precise look at the documents it shows pin 2 voltage should be 0.0 and pin 3 voltage should be 0.1 v which is almost the same voltages I have measured. Also document shows with these inputs there should be 2.75 v at the output but we have 14 v. This shows we have a faulty parts here. Any advice how to proceed?

12. ## Re: OP07 circuit output voltage?

this question appeared in this thread
13.9 V instead of 2.75 v, Which parts are failing?

so my question is what are umsch1 and umsch2 connected to?
umsch1 is directly connected to the inverting input
unsch2 is connected to inverting input through a resistor

where is the adjustment you mention in post #6?

are you sure all of the components are correct?
what did you get when you simulated this circuit?

13. ## Re: OP07 circuit output voltage?

With precise look at the documents it shows pin 2 voltage should be 0.0 and pin 3 voltage should be 0.1 v which is almost the same voltages I have measured. Also document shows with these inputs there should be 2.75 v at the output but we have 14 v. This shows we have a faulty parts here. Any advice how to proceed?
when you put the probes on - the current drawn by the meter affects the reading, when you take the robes off the voltage will stray back to something else ...

unless you have a 1000 Meg-ohm meter ...

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you need to read up majorly on op-amps and feedback around opamps, and input current and biasing of same ...

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this op amp has Vios of 30 - 75uV so in a proper ckt the inputs will be only this far apart...

14. ## Re: OP07 circuit output voltage?

Originally Posted by wwfeldman
this question appeared in this thread
13.9 V instead of 2.75 v, Which parts are failing?

so my question is what are umsch1 and umsch2 connected to?
umsch1 is directly connected to the inverting input
unsch2 is connected to inverting input through a resistor

where is the adjustment you mention in post #6?

are you sure all of the components are correct?
what did you get when you simulated this circuit?
umsch1 and umsch2 are not relevant in this stage so forget these.
Adjustments mentioned in post #6 also is not relevant in this standby stage.
Component are OK.
Haven't done simulation. I am not good in electronic and electronic circuits simulation.

For the moment important things are : pin2 voltage =0.03 v, Pin3 voltage=0.1 v. According to the documents at this stage pin2 should have 0.0 v and pin3 should have 0.1 v and output should have 2.75 v and I have to find out why it is 14 v and fix it. Then I can turn the closed loop feedback on in order for the circuit to start closed loop control. After control starts pin3 will start going up from 0.1v up to 2.5 v. Pin 2 should follow pin 3 closely until its voltage reach the same 2.5v (+/- 10 percent) using the feedback from output otherwise I will get "actual value greater than setvalue+10% (i.e. overshoot)" and system will turn off by itself which is happening now and I should fix this problem.

15. ## Re: OP07 circuit output voltage?

respectfully, if pin 3 (+) is 0.1V and pin2 is lower than this - the o/p will go high to rail - thus there is no fault

16. ## Re: OP07 circuit output voltage?

I am also thinking so but the stupid Siemens document says output should be 2.75 v and this puzzled me too. I am not very good with circuits. Probably parts around the OP07 somehow should decrease the gain and prevent this. This is what I am trying to find.

In normal operation (in closed loop control) pin3 should have 2.5 v and pin2 should follow it by below 10 percent difference and output should have 2.75 volts.

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17. ## Re: OP07 circuit output voltage?

it is impossible to offer helpful comment without the full circuit ...

18. ## Re: OP07 circuit output voltage?

I have attached the whole U-regulator circuit if it can help

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I have attached the whole U-regulator circuit if it can help

19. ## Re: OP07 circuit output voltage?

Japanese schematics are far easier to read than Siemens ones. Your image quality is also poor.

Focus on the the green circle readings to trace back why the 2.75V is failing for the required for pre-calibration. Since these Op Amps saturate 2 or so volts away from +/-15V rail anything close to that means it is "open loop" or saturated hence not regulating.

Trace forward from +/15V to the voltage dividers, relay which then combines the feedback voltage into the 1st stage.

I expect 3.75V but may have misread a resistor value.

I used Irfanview to edit your image which is also enlarged below.

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20. ## Re: OP07 circuit output voltage?

Nice explanation but honestly with my poor electronic knowledge I should say I didn't get much what to do. Could you please put it in a stepwise procedure what should I do to get close to the problem.

To me and to make it simpler since voltages of pin2 and pin 3 are known (0.03 and 0.1) one should try to determine the output of the OP07 by calculation or simulation (I can't because of my poor knowledge of electronics). If it was close to 14 v then Siemens document is wrong for sure and should be a misprint or something like that but if it came out about 2.75 then one should focus on the OP07 circuit and parts around it to find the faulty part. right?

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