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Single Supply problem with OP07 and OPA227

LAXMI KANT TIWARI
Genius 3345 points
Other Parts Discussed in Thread: OP07, OPA227, LM324

Hi,

    I am using OP07 and OPA227 opamps for my analog filtering circuits.  I have a problem with OP07 and OP227 with single supply mode. It is running fine when I use dual supply but on single supply final output is clipping by almost 1 volt from Vcc and GND i.e. I am only getting 1V to 4V volt swing on given 5V Vcc with 2.5V reference. And sometimes I get strange output when I use OPA227 such as 50 Hz peak to peak saturated noise however I have included notch filter as well as power decoupling capacitor on power lines. 

1. now the question is why I am not getting the full     swing at the output? 

2. Why the same circuit is running with OP07 but not with OPA227

3. Can you suggest low noise single supply opamp which I can use with 3.3V Vcc or lower than 3.3V Vcc? 

  • 0
    TI__Expert 4126 points

    Hello Laxmi kant

    The OPA227 is not a rail to rail output opamp

    Hence the maximum output swing on a +5V and 0 V supply       is only 2V min to 3V max

    I would recommend using a rail to rail opamp to get the output swing from 0V - 5 V

    Please refer to the link above for a rail to rail low noise opamps

    I have filtered the parameters of op amps to suit your needs

    Thank you 

  • 0 in reply to Shreenidhi Patil
    Genius 3345 points
    Thanks for your quick reply. I think we are having same problem with OP07 also?
  • 0 in reply to LAXMI KANT TIWARI
    TI__Guru**** 166666 points
    Laxmi,

    Yes, OP07 also.
  • 0 in reply to Ron Michallick
    Genius 3345 points

    Hello, I have tested my analog circuit with LM324 rail to rail DIP package opamps, here also I am not getting the full swing. Circuit output is clipping after Vcc-1.3V i.e. now output swing is limiting from 0V to Vcc-1.3V. I have tested it with 3.3V as well as 5V supply with the 1.8V reference voltage.

    One more point is worth of mentioning here it seems single supply circuit is more prone to noise and signal distortion. is it true ? or something is wrong with my circuit?

    Please refer to the video here I don't know why my circuit is picking input signal just for 1s or less then it picks 50Hz peak to peak noise and then again after some time it goes zero to actual signal then noise and so forth. there you can also see max voltage is 3.7v on 5V Vcc. 

  • 0 in reply to LAXMI KANT TIWARI
    TI__Expert 4126 points
    Hi Laxmi,
    The LM324 output can reach max Vcc- 1.5V.
    It is capable of reaching the rail voltages only towards Vcc- , in your case which is GND

    As you have biased it to 5V , the maximum output it can go (5V -1.5V)= 3.5V

    I wouldn't believe the noise is due to the very fact that your biasing it with a single supply


    Please look out for opamp parts which are labeled as "rail to rail" input and output
    Also i would recommend to go through the input and output limitation video in the link below
    It would help you a lot in understanding the reason for the behavior you are observing above

    www.ti.com/.../precision-amplifier-precision-labs.page

    Also also please refer to the stability video series in the above link

    It will help you debug the oscillations at the output of your op amp
    The videos explain some common reasons for the oscillation at the output of the oamp



    Thank you