Problem with schema on NI Multisim

Discussion in 'Homework Help' started by rio7, Jan 16, 2015.

  1. rio7

    Thread Starter Member

    Jan 1, 2015
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    Good morning, I have schema ( picture ), but I don't know how to created it on NI Multisim ( I do it, but this schema looks like... You can see in my attached files ).
    I must have and component who can show me the oscilograms. How should I do it ?
    And one more problem: I don't find component - VT2, VT3 and VT4 ( in picture ) in NI Mulstisim ( 13 ) program.



    Thank You!
     
    Last edited: Jan 16, 2015
  2. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    What is the source of your schematic picture? It looks like you drew it in mspaint. Are you not showing all the information available to you?

    VTx where x is a number is the component designation. Multisim identifies transistors differently. Cx would be capacitor, Rx would be resistor, Qx or Tx or in the case of your picture, VTx is transistors. Lx is inductors. Of course the V could mean Virtual ... or perfect. VD1 is a diode.

    You can insert some NPN and PNP transistors as appropriate to make the schematic in multisim.
     
    Last edited: Jan 16, 2015
  3. rio7

    Thread Starter Member

    Jan 1, 2015
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    Yea, I drew it on windows paint. I have just these numbers of it:

    P(out)= 2W
    R(load/strain/workload) = 12Ω
    Uin = 20mV
    F = 300 Hz to 7 kHz
    Rin = 2 kΩ
    M <= 3dB
    And I have created audio amplifier.

    I attachement better schema of it.

    But I have problem:

    I add 20mV ( I try and 20, 100 V ) in AC voltage, but osicilograms showing something wrong.. I attachement some picture of it.
    What can be problem at ?
     
  4. crutschow

    Expert

    Mar 14, 2008
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    One error I see is no connection dot between bias resistors R3, R4, and Q1's base, thus Q1 has no bias.
     
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  5. rio7

    Thread Starter Member

    Jan 1, 2015
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    Thank You! But right now I got still bad simulated. What it's could be wrong ?
     
    Last edited: Jan 17, 2015
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    You have your input at 100 volts peak.....what is it suppose to be?

    Your Vcc is only 15 volts dc.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    He tried with different voltages 100V, 20V and 20mV, but the 100V is really crazy for a input, since the input never great than 2V.
     
  8. rio7

    Thread Starter Member

    Jan 1, 2015
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    I can change voltages to 2V or smth else, but oscilograms showing no sinusoid. What should I do ? Maybe my schema is wrong ?
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    The value of resistors quite strange, you could change the position first,.
    1. Cut off the connection from R5 and C4.
    2. Connecting R5 to GND.
    3. Connecting C4 to the e of Q1.
    And try again, when it can do the amplifying then you can adjust the value of resistors.
     
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  10. rio7

    Thread Starter Member

    Jan 1, 2015
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    I do it. I attachment picture. But I see what C4 ir going/flashing to red color.
    And oscilograms showing still not really sinusoid.
    P.S. What wrong with resistors position ?
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    during the move of the capacitor, you have made a break in one of the nets:

    [​IMG]

    Bertus
     
  12. rio7

    Thread Starter Member

    Jan 1, 2015
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    I understand clearly, I have to do this ?

    Test1.png
     
  13. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Check this file
     
  14. ScottWang

    Moderator

    Aug 23, 2012
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    The negative of C4 and the c of Q2, R4 and 0V of input signal, they must be connecting to GND, I 'm sure why you disconnected them?

    And set the Vin max to 2V.
     
    Last edited: Jan 18, 2015
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    No, the cap would short the input signal.
    Here I corrected the circuit in paint:

    [​IMG]

    Bertus
     
  16. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    No way, the correct circuit should look like this
    3.PNG
     
  17. ScottWang

    Moderator

    Aug 23, 2012
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    The problem of R5 and C5 as I mentioned on #9, do you think is it ok?
     
  18. bertus

    Administrator

    Apr 5, 2008
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    Hello Jony,

    I was just following the instructions of ScottWang in post #9.

    Bertus
     
  19. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    R5 and C5 should be connected in series.
    Because this circuit should work as a poor's man op amp. And Q1 is a differential amplifier (base a "+" input and emitter as a"-" input) and the closed loop gain is equally to
    Av =(1+ R6/R5) ≈ R6/R5

    Here you have a very similar circuit

    [​IMG]
     
  20. ScottWang

    Moderator

    Aug 23, 2012
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    No, they are different, in your new circuit that the R4 and C3 is in parallel with the Vce, and the c of 3906 has 8.2k to provide the dc quiescent current to ground, the R3(2.7K) provide the feedback current.

    The circuit of bertus on #15, R6 is the feedback current, R5 provide the dc quiescent current to ground, you can't using the feedback resistor to replace the e resistor, if you do that then the e will loss the dc quiescent current.
     
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