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[SOLVED] Op-Amp Positive Supply drops down..........

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SACHIN C

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Dear All,

Pls help me out,Whenever i am connecting Sinewave(5Vp-p\50Hz) generated using XR2206 to TL074 Non-Inverting Terminal used as an difference op-amp,the voltage of sinewave gets reduced to 1.68Vp-p & simultaneously Op-Amp +15 V drops to 4.68V.

I have connected +15 V & -15 V to the Op-amp :smile:

Is 680E connected for current limit affects?
or
XR2206 is not capable to deliver the amount of current required by the TL074?
 

680E is the value of resistor connected for TL074 op amp current restriction.........
 

Dear All,
Pls help me out can we apply +15V & -15V to TL074 opamp & 741 Op-Amp as an supply voltage?:!:
If yes than what should be the Limiting resistor like TL074 needs 1.6mA per Amplifier?:smile:

Thanks.....
 

Pls find the attached file for circuit.....
XR2206 used two :for Triangular & Sinewave Generation but,in circuit shown single.


Thanks & Waiting for valuable help......:smile:
 

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  • Circuit.jpg
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Where is the 680 ohm resistor you keep talking about? I cannot see it.

Keith
 

keith
680 ohm resistor connected for current limit in between 7815 & opamp +15v......
I am confused with opamp power supply because i have used +15v & -15V supply for Op-Amp is it fine or exceeds opamp max.?

Thanks......:smile:
 

The TL074 can run up to 36V total supply so +/-15V is fine. You should NOT put resistors in the supply line! Sometimes this might be done with a small resistor and decoupling capacitor after it but otherwise you are simply going to end up with a circuit which doesn't work.

The resistor values in your circuit seem rather low. I haven't checked in detail but the opamp may struggle with such low values.

Keith
 
Keith
so i didn't need to connect current limiting resistor for opamp?
Also i used 741 opamp to generate 3.5Vp-p Sinewave with same suppl +15V & -15V is that fine?
IS XR2206 capable to deliver the Tl074 required current (XR2206 Sinewave Output connected to TL074 Pin 3 & Pin 10 Non-Inverting)?
At 1st stage the difference must be obtained at the pin 1,but it is variable upto 7Vp-p(Pin 2 Inverting Sinewave 3.5Vp-p & Pin 3 non-Inverting Sinewave 5.10Vp-p)?
Also XR2206 output connected to buffer and then buffer output to opamp(Pin 3) still not working,the positive cycle of sinewave at output varies in amplitude?


thanks.....:smile::cool:
 
Last edited:

As I said, you rarely put resistors in opamp power supplies and not for current limiting anyway - only for removing high frequency noise coupling.

741 is fine on +/-15V. I think you need to increase the resistor values. I wouldn't normally be using less than 2k ohms anywhere on a circuit like that, using TL074s which have a JFET input. 22k and 220k would be typical resistors you might be using. The opamps will not be able to drive large voltage swings into the low value resistors.

Keith
 
Keith
Thanks for explaining the resistor function in between Op-amp and power supply....:smile:
How can a resistor only isolate high frequency noise or as you said we need to use cap also in that situation?
Surely i will revert back after changing the resistor as 22ohm by 22k & 220ohm by 220k

Thanks.....:smile:

- - - Updated - - -

After replacing 22ohm by 22k & 220ohm by 220K the positive signal trip problem solved but, the stage wise output is not proper?
Pls suggest me the proper resistor required for the above attach circuit????:!:


thanks.......

- - - Updated - - -

After replacing 22ohm by 22k & 220ohm by 220K the positive signal trip problem solved but, the stage wise output is not proper?
Pls suggest me the proper resistor required for the above attach circuit????


thanks.......
 
Last edited:

Dear all,
What will happen if i replace Ground by negative supply ground for above attached circuit???????:!:


Thanks:smile:
 

Kam1787,
Using single supply for Op-Amp,it causes level shift of Sinewave with 3.58vdc above X-axis .
So,i thought using dual supply which can give us DC shift above & below X-Axis,so that it can be feed to the Comparator.:?:

Thanks,:smile:
 

Do you mean truncation (and not level shifting)?

I think you had meant to say in the prior post , "What will happen if I INCLUDE Ground (with +- voltage supply) for above attached circuit?"

You had stated, "I have connected +15 V & -15 V to the Op-amp" so I had presumed it was +15V, Ground, and -15V


Normally connecting a dual power supply assumes the use of Ground. Otherwise we would say it is a [single-ended] power supply of 30V.
 

Kam1787,
Actually I powered Opamp with +-15V but,Sinewave generated Using XR2206 With +15V & Ground so the Sinewave is with respect to ground is lifted?

Thanks,:smile:
 

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