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LM5041: Need help to debug TINA simulation circuit

Jim Brinkhurst1
Mastermind 44550 points
Part Number: LM5041
Other Parts Discussed in Thread: LM258

Hi 

Can someone please help resolve the simulation problems with my customer's TINA circuit attached? I did try to run a transient simulation and I get an error message with issues with a few nodes.

Here are the circuit goals and some issues from the customer:

The transfer ratio of the current sense is 100; the voltage ratio of the transformer is 8/3; and the frequency of the PWM generator is supposed to be 300KHz, but I was not able to set that because when I open the voltage generator VG1, there is no field to set the frequency. The input voltage is 28V and the output voltage is supposed to be 28V. I plan to do the transient and the AC analysis. Please, could you help me in troubleshooting the design?

One more thing I would like to draw your attention to is the ground at the secondary of the transformer. It should be different from the ground at the primary, but I was not able to find another ground symbol to do that.

Thanks for your help!

Best regards,

Jim B

/cfs-file/__key/communityserver-discussions-components-files/196/LM5041-Simulation-Issue.TSC

  • 0
    TI__Mastermind 27325 points

    Hi Jim,

    The LM5041 frequency is not set by the Pulse Generator (VG1 in the TINA schematic) connected to the "TIME" pin. The TIME pin controls the amount of output dead-time or overlap and is currently set for overlap by R18. FYI - if you double click the VG1 source, a window pops up, single click "Pulse", the single click the three dots and the signal editor window pops up. Here you can see the function that is currently selected is non-periodic but could be changed if desired. See screen shot below:

    The frequency is set by RT and is currently set up for 252 kHz based on R14=20.5 k. I also tried running the sim and get a current error related to U2. Everything looks correct, they way the model is used. I will check with some colleagues and get back to you by end of this week.

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    TI__Mastermind 27325 points

    Jim,

    There may be other aspects of this sim that need further development to achieve the design goal but to get the sim running, you need to apply initial conditions to the capacitors around U2. I applied initial voltage to C10=10V and C8=5V. Capacitors with prebiased voltage such as C10 that has 10 V across it  but the initial voltage at the start of the sim is 0 V as defined in the C10 parameters - simulators in general choke on this scenario and the same current through an inductor. This can often be the cause of convergence errors where the simulator is unable to resolve the conflict in voltage (or current). When you click "Analysis" -> "Transient", then make sure the radio button "Use Initial Conditions" is selected. The error seen previously is cleared and the sim runs but very slowly. Try reducing the step size, sim time, etc to speed things up initially. For the issue of different Ground symbols, I did not find an option to visually display a different Ground symbol but...if you right click on the GND symbol before it is placed on the schematic, then click "Properties" you can assign different Ground references to various portions of the circuit (GND1 vs GND2 for example). I have not tried running the sim with separate GND references but that is how you differentiate. One final thing that looks unusual is the LM258 OP AMP (U1, U5), where every pin  is shown as pin 9? This may be an error in the model creation and perhaps it's only in the visible attributes and the model itself is ok - it just looks weird? You might consider a different OP AMP? Good luck with it.

    Regards,

    Steve M