+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Newbie level 5
    Points: 634, Level: 5

    Join Date
    Aug 2009
    Location
    chd
    Posts
    10
    Helped
    0 / 0
    Points
    634
    Level
    5

    wein bridge oscillator

    hello,
    i am doing a practical on lm 741. i want to make it to use it as an wein bridge oscillator.the value of c1=c2=0.01uF, R1=R2=3K, Rf=2k, Ra=1k.accordingly the output frequency should be 5khz.bt my circuit is not working like.even its frequency is not stable at all.i think my circuit is not working.please tell me where is the fault.

    the link for the image is given below:

    •   Alt29th March 2010, 07:08

      advertising

        
       

  2. #2
    Advanced Member level 5
    Points: 74,061, Level: 66

    Join Date
    Oct 2004
    Location
    West Coast
    Posts
    7,942
    Helped
    2324 / 2324
    Points
    74,061
    Level
    66

    Re: wein bridge oscillator

    To make it working you need a symmetrical power supply, for example : [+5V] - 0V - [-5V] .. see attached picture ..
    Without that symmetry the inputs are incorrectly biased ..

    Rgds,
    IanP
    :D



  3. #3
    Newbie level 5
    Points: 634, Level: 5

    Join Date
    Aug 2009
    Location
    chd
    Posts
    10
    Helped
    0 / 0
    Points
    634
    Level
    5

    Re: wein bridge oscillator

    thanks for the reply. but i am still confuse. i did not got what do you mean by symmetrical power supply as i am using regulated power supply for biasing.i have to use +5 and - 5 volt supply ?just give me idea about the symmetrical power supply and how to implement it.



  4. #4
    Advanced Member level 5
    Points: 74,061, Level: 66

    Join Date
    Oct 2004
    Location
    West Coast
    Posts
    7,942
    Helped
    2324 / 2324
    Points
    74,061
    Level
    66

    Re: wein bridge oscillator

    You have to create situation similar to connecting two batteries (or two power supplies) in series, thus creating positive and negative supply with reference to the common connection, which you can call “virtual ground”, 0V or GND .. see attached picture or this website:
    http://tangentsoft.net/elec/vgrounds.html

    Rgds,
    IanP
    :D



    •   Alt29th March 2010, 11:45

      advertising

        
       

  5. #5
    Member level 4
    Points: 1,286, Level: 8

    Join Date
    Oct 2009
    Location
    Pakistan
    Posts
    72
    Helped
    1 / 1
    Points
    1,286
    Level
    8

    Re: wein bridge oscillator

    The 741 OP-Amp Ic is a device which require dual supply to be operated.



  6. #6
    Advanced Member level 5
    Points: 39,414, Level: 48
    Achievements:
    7 years registered
    LvW's Avatar
    Join Date
    May 2008
    Location
    Germany
    Posts
    5,658
    Helped
    1697 / 1697
    Points
    39,414
    Level
    48

    Re: wein bridge oscillator

    Hello preetikarki,

    * The comment from IanP is correct since it is recommended to operate with a dual supply (for single supply the circuit looks a bit more complicated.)

    * The comment from yasir is not correct. The 741 does not require a split supply.

    * However, the most important point: Your circuitry is wrong!:

    The resistive feeback must be inverting to form an non-inverting amplifier with a gain of (slightly above) 3. Thus, change the resistor ratio an d connect this path to the neg. opamp input.
    The WIEN path has to be connected to the non-inv. opamp input.

    *Please note, that the circuit is called WIEN oscillator. I know that in several books and articles the name is spelled incorrectly as "WEIN



  7. #7
    Super Moderator
    Points: 49,672, Level: 54
    Achievements:
    7 years registered
    keith1200rs's Avatar
    Join Date
    Oct 2009
    Location
    Yorkshire, UK
    Posts
    10,877
    Helped
    2074 / 2074
    Points
    49,672
    Level
    54

    wein bridge oscillator

    As IanP has also said, you do need a ground reference for your power supply as well. It cannot be floating as it currently is.

    Keith.
    I started life with nothing and I've still got most of it left. (Seasick Steve)



    •   Alt29th March 2010, 15:09

      advertising

        
       

  8. #8
    Full Member level 5
    Points: 3,271, Level: 13
    Achievements:
    7 years registered
    _Eduardo_'s Avatar
    Join Date
    Aug 2009
    Location
    Argentina
    Posts
    271
    Helped
    112 / 112
    Points
    3,271
    Level
    13

    Re: wein bridge oscillator

    Fix the opamp inputs error and replace R1, R4 by two 2*R values to provide an offset voltage.

    For minimum distortion, R2 (22k) must be the minimum value that assure the oscillation.





  9. #9
    Advanced Member level 5
    Points: 47,546, Level: 53
    Achievements:
    7 years registered
    Audioguru's Avatar
    Join Date
    Jan 2008
    Location
    Toronto area of Canada
    Posts
    8,258
    Helped
    1925 / 1925
    Points
    47,546
    Level
    53

    wein bridge oscillator

    A very old LM741 cannot drive resistors as low as 470 ohms. Increase their value then decrease the value of the capacitors to keep the same frequency.

    Your very simple circuit does not have an amplitude stabilization circuit so the output will be clipped with severe distortion.



--[[ ]]--