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Huge difference between spice simulation and acutal breadboarded circuit

Discussion in 'Electronic Basics' started by [email protected], Mar 31, 2005.

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  1. Guest

    I am trying to use the TLV2241 DIP package IC to make a relaxation
    oscillator(square wave oscillator using positive feedback). I first
    simulated the design in spice (both ORCAD PSPICE and WINSPICE). I used
    the SPICE model of the TLV2241 provided in the data sheet provided by
    TI.COM . Please see the spice circuit file below.

    Problem: In the simulated version I get an oscillation period of approx
    6.2ms. However when I built the circuit using the chip I actually got a
    frequency of 19Hz(Period approx 52ms)
    I have made sure that all components are close to the specs as
    specified in the spice simulation
    Question) Is the model provided by TI, as shown below, adequate to
    accurately model the opamp. Please suggest why is there such a
    disparity between spice simulation(s) and the actual circuit?
    Thanks
    SPICE CIRCUIT FILE FOR SQUARE WAVE GENERATOR USING TLV2241
    ----------------------------------------------------------
    *Relaxation oscillator using a single supply opamp
    * connections: non-inverting input
    * | inverting input
    * | | positive power supply
    * | | | negative power supply
    * | | | | output
    * | | | | |
    ..SUBCKT TLV2241 1 2 3 4 5
    C1 11 12 9.8944E-12
    C2 6 7 30.000E-12
    CEE 10 99 8.8738E-12
    DC 5 53 DY
    DE 54 5 DY
    DLP 90 91 DX
    DLN 92 90 DX
    DP 4 3 DX
    EGND 99 0 POLY(2) (3,0) (4,0) 0 .5 .5
    FB 7 99 POLY(5) VB VC VE VLP VLN 0 61.404E6 -1E3 1E3 61E6 -61E6
    GA 6 0 11 12 1.0216E-6
    GCM 0 6 10 99 10.216E-12
    IEE 10 4 DC 54.540E-9
    IOFF 0 6 DC 5E-12
    HLIM 90 0 VLIM 1K
    Q1 11 2 13 QX1
    Q2 12 1 14 QX2
    R2 6 9 100.00E3
    RC1 3 11 978.81E3
    RC2 3 12 978.81E3
    RE1 13 10 30.364E3
    RE2 14 10 30.364E3
    REE 10 99 3.6670E9
    RO1 8 5 10
    RO2 7 99 10
    RP 3 4 1.4183E6
    VB 9 0 DC 0
    VC 3 53 DC .88315
    VE 54 4 DC .88315
    VLIM 7 8 DC 0
    VLP 91 0 DC 540
    VLN 0 92 DC 540
    ..MODEL DX D(IS=800.00E-18)
    ..MODEL DY D(IS=800.00E-18 RS=1M CJO=10P)
    ..MODEL QX1 NPN(IS=800.00E-18 BF=27.270E21)
    ..MODEL QX2 NPN(IS=800.0000E-18 BF=27.270E21)
    ..ENDS

    XOP1 3 1 4 0 2 TLV2241
    Cout 2 6 0.033uF
    RF 1 6 9.99K
    CF 1 0 10uF
    R2 6 3 1.001K
    R1 3 0 19.97K
    VS1 4 0 5V
    ..TRAN 0.01ms 100ms
    ..PROBE
    ..PLOT TRAN V(2)
    ..END
     
  2. Fred Bloggs

    Fred Bloggs Guest

    Change the lines:
    to:

    RF 1 2 10K
    CF 1 0 10uF
    R2 2 3 20K
    R1 3 0 20K

    and add:

    R4 3 4 20K

    The period should be 1.4*RF*CF=140ms if you want more like 5ms then make
    CF=0.33uF.
     
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