TL494 buck converter, trouble simulating

Discussion in 'The Projects Forum' started by Tryingtomakethiswork, Dec 21, 2013.

  1. Tryingtomakethiswork

    Thread Starter New Member

    Dec 21, 2013
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    Hey all, new here. Sorry if this thread is misplaced.

    I've been working on a project using a TL494 PWM chip to drive a buck converter. Problem is my simulation is having convergence errors. Attached is the picture of my schematic. If I replace the TL494 with a function generator I can run the simulation just fine, but when I use the TL494 and try to incorperate a feedback loop I can't seem to get it to work. Would love a solution, thanks in advance to all those that help out!

    [​IMG]

    Sorry if this picture doesn't work, it's been attached as well.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What error messages?
     
  3. Tryingtomakethiswork

    Thread Starter New Member

    Dec 21, 2013
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    These supply currents failed to converge:

    I(X_U3.xinsttl494.Ev103) = -36.90nA \ -110.41pA
    I(V_V2) = 1.967uA \ 95.04nA

    These devices failed to converge:
    Q_Q3 Q_Q4 X_U3.xinsttl494.X_U3.X1.Q1 X_U3.xinsttl494.X_U3.X2.Q1
     
  4. Tryingtomakethiswork

    Thread Starter New Member

    Dec 21, 2013
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    Forgot to add an updated picture of the circuit. Here it is
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I'd try to run an LTspice sim, but I don't have a model for the TL494 :(
     
  6. Tryingtomakethiswork

    Thread Starter New Member

    Dec 21, 2013
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    Does LTspice just not have a library for it? You're the second person who was sad about not being able to help due to using LTspice. I'm super new to the simulating world, so I don't know much about anything other than Orcad's PSPICE, and even then it's minimal :(
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Not part of LTspice download and not available from the Yahoo LTspice User Group.
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Dont understand what you mean by Convergence Errors, also why are you pulsing L2 with 32V and looking to get 16V output across C3, using a N chan mosfet as a follower, when your supplying it with 16V already?
     
    Last edited: Dec 21, 2013
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Why have you got pin 11 of the 494 grounded?

    I've now found a sim model on Yahoo for the '494.
    With a few changes to your circuit I got the sim to run initially, but got a 'time step too small' error at ~1ms sim time when the ripple on the output voltage across R12 had dropped to a small value.
    Here's the amended circuit:
     
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