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UC3845 Pspice Simulation Convergence issue

Urmi Shah
Prodigy 50 points
Other Parts Discussed in Thread: UC3845

Hello,

I am facing convergence issue with the Pspice Model of UC3845 for 2-switch forward converter. The two freewheeling diodes, MOsfets and the UC3845 fail to converge. Can anybody guide me on what settings or changes must be done in order to debug this issue?

  • 0
    TI__Genius 13660 points

    Hi Urmi,

    Could you share the schematic, actually this is the first time for me UC3845 is used for 2-switch forward application.

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Prodigy 50 points

    Hi Teng, 

    Please find the attached snapshot of the simulation schematic. 

    For this I have tried autoconvergence but still there is convergence error as below:

    These devices failed to converge:
    X_U115.G_Miller X_U115.G_Coss X_U125.XDRIVE.M1 X_U125.XDRIVE.M2 Q_Q6
    Q_Q5

    Last node voltages tried were:

    NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE NODE VOLTAGE


    ( D) 2883.2000 ( CS) 4127.0000 ( FB) 3.1089 ( DRV) 112.8E+03

    ( V18V) 12.1970 ( VGSL) 11.44E+03 ( VGSU) 798.7E+03 (VBULK) 325.0000

    (N2075040) 70.60E+03 (N2075050) 1109.4000

    (N2075056) 576.7700 (N2075074) 12.5060

    (N2075542) 12.0040 (N2076336) 12.7830

    (N2076356) 4.5646 (N2076452) 3.1095

    (N2076480) 3.1089 (N2076484) 20.0000

    (N2076628) 13.3690 (N2076698) 5.1060

    (N2076714) 2108.4000 (N2076836) 13.5640

    (N2076870) -1.2947 (N2076982) 4.5609

    (N2078287) 1.017E+06 (N2078291) 1.015E+06

    (N2078375) 797.8E+03 (N2078381) 791.4E+03

    (N2078429)-786.9E+03 (N2078453) 112.8E+03

    (N2078587)-377.5E+03 (N2078691) 229.8E+03

    (N2078821) 227.3E+03 (N2078891) 10.53E+03

    (X_U112.5) 1.017E+06 (X_U112.6) 1.017E+06

    (X_U114.d) 9.999E+09 (X_U114.g) 5375.0000

    (X_U114.s) 4127.3000 (X_U115.d) 10.00E+09

    (X_U115.g) 792.6E+03 (X_U115.s) 791.4E+03

    (X_U123.4) 3.1078 (X_U123.6) 12.7830

    (X_U123.7)-7.970E-09 (X_U123.8)-17.12E-09

    (X_U124.4) 7.0559 (X_U124.5) 1773.4000

    (X_U124.6) 1774.8000 (X_U124.7) 1773.4000

    (X_U125.5) 0.0000 (X_U125.6) 5.0000

    (X_U125.7) 0.0000 (X_U125.8) 4.6418

    (X_U125.9) 2.1089 (N20784690) 753.0E+03

    (X_U112.20) 4127.0000 (X_U112.21) 4127.0000

    (X_U114.aa) -79.9980 (X_U114.ba) -80.0010

    (X_U114.d1)-786.9E+03 (X_U114.g2) 11.44E+03

    (X_U114.ss) 4127.0000 (X_U114.sx) 4127.3000

    (X_U114.Tj) 27.0000 (X_U115.aa) -79.9960

    (X_U115.ba) -80.0010 (X_U115.d1) 325.0000

    (X_U115.g2) 798.7E+03 (X_U115.ss) 791.4E+03

    (X_U115.sx) 791.4E+03 (X_U115.Tj) 27.0000

    (X_U125.10) 5.0000 (X_U125.11) .5468

    (X_U125.12) 1.6405 (X_U125.13) 5.0000

    (X_U125.16) .5468 (X_U125.19) 20.0000

    (X_U125.21) 5.0000 (X_U125.22) 5.0025

    (X_U125.50) 5.0000 (X_U125.51) 0.0000

    (X_U114.d1k)-786.9E+03 (X_U114.d1z)-786.9E+03

    (X_U115.d1k) 325.0000 (X_U115.d1z) 327.8800

    (X_U125.150) 5.0000 (X_U125.191) 20.0000

    (X_U114.11xy)-907.3E+03 (X_U114.Alfa) 2.000E-12

    (X_U114.d1zd)-786.9E+03 (X_U114.Dev1) 9.999E+09

    (X_U114.Dev2) .0569 (X_U114.Dev3) 0.0000

    (X_U114.dfet)-907.3E+03 (X_U114.edep) 9.967E+09

    (X_U115.11xy)-120.1E+03 (X_U115.Alfa) 2.000E-12

    (X_U115.d1zd) 327.8800 (X_U115.Dev1) 9.999E+09

    (X_U115.Dev2) -2.0068 (X_U115.Dev3) 0.0000

    (X_U115.dfet)-120.1E+03 (X_U115.edep) 9.968E+09

    (X_U114.11xxx) 4127.0000 (X_U114.Alfa2) 43.30E-12

    (X_U114.Dev1c) 9.999E+09 (X_U114.Dev2c) .0569

    (X_U114.Dev3c) 0.0000 (X_U114.Val_T)-5.400E-12

    (X_U115.11xxx) 791.4E+03 (X_U115.Alfa2) 43.30E-12

    (X_U115.Dev1c) 9.999E+09 (X_U115.Dev2c) -2.0068

    (X_U115.Dev3c) 0.0000 (X_U115.Val_T)-5.400E-12

    (X_U125.XAMP.2) 2.7521 (X_U125.XAMP.3) 2.9186

    (X_U125.XAMP.5) 2.5281 (X_U125.XAMP.6) 2.5281

    (X_U114.d_dedep) 9.998E+09 (X_U115.d_dedep) 9.999E+09

    (X_U125.XAMP.10) 2.5530 (X_U125.XAMP.13) 2.3348

    (X_U114.d1bvdss1)-786.9E+03 (X_U115.d1bvdss1) 325.0000

    (X_U125.XDRIVE.2) 252.2700 (X_U125.XDRIVE.3) 252.2700

    (X_U125.XLATCH.3) 5.0000 (X_U125.XLATCH.4) 5.233E-09

    (X_U125.XLATCH.7) 43.12E-09 (X_U125.XLATCH.8) 5.0000

    (X_U125.XLATCH.9) 0.0000 (X_U125.XLATCH.10) 5.0000

    (X_U125.XToggle.3) 5.0000 (X_U125.XToggle.4) 5.0000

    (X_U125.XToggle.7) 43.12E-09 (X_U125.XToggle.8) 5.0000

    (X_U125.XToggle.9) 0.0000 (X_U125.XToggle.10) 5.0000

    (X_U125.XLATCH.X1.5) 5.0000 (X_U125.XLATCH.X2.5) 0.0000

    (X_U125.XLATCH.X3.5) 0.0000 (X_U125.XLATCH.X4.5) 5.0000

    (X_U125.XLATCH.X5.5) 5.0000 (X_U125.XLATCH.X6.5) 0.0000

    (X_U125.XLATCH.X7.3) 0.0000 (X_U125.XLATCH.X8.3) 5.0000

    (X_U125.XToggle.X1.5) 5.0000 (X_U125.XToggle.X2.5) 0.0000

    (X_U125.XToggle.X3.5) 0.0000 (X_U125.XToggle.X4.5) 5.0000

    (X_U125.XToggle.X5.5) 5.0000 (X_U125.XToggle.X6.5) 0.0000

    (X_U125.XToggle.X7.3) 5.0000 (X_U125.XToggle.X8.3) 5.0000

    Request you to help me with this issue.

  • 0 in reply to Urmi Shah
    Prodigy 50 points

    Hi Teng,

    Did you get a chance to go through the schematic. The voltage at output of the IC is going high upto 200V and so the Mosfet voltages are going out of range.

    Request you to help me with this.

    Thanks,

    Urmi

  • 0 in reply to Urmi Shah
    TI__Genius 13660 points

    Hello Urmi,

    This is a probably a simulation setup issue.

    You can share me the simulation file or send to my email  teng-feng@ti.com    if it is unavailable here

    Regards,

    Teng