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This is the second time I'm trying to simulate a SEPIC converter today. First I went with LT3959, but after hours of trying to make it work, I assumed there is something wrong with the component and it would be easier to choose another component and everything would work.

The second time i went with LT8364 and again I did everything as the datasheet said, placed realistic components (parasitic C,L,R) but again I can't make it to work.

I'm using the newest version of LTspice. (LTspice XVII (x64), May 4 2018

The problem that occurs is that the output voltage is 0V.

enter image description here

This is my schematic:

enter image description here

Vin and Vout:

enter image description here

Can anyone help me? Should I instal older version of LTspice?

*.asc file: link

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  • \$\begingroup\$ If you make the .asc file available somewhere people that want to test it themselves have an easier time. \$\endgroup\$
    – PlasmaHH
    Commented May 8, 2018 at 7:50
  • \$\begingroup\$ Why did you couple L1 and L2 to form a transformer? \$\endgroup\$
    – PlasmaHH
    Commented May 8, 2018 at 8:02
  • \$\begingroup\$ Because it reduces the output ripple, you can do it without coupleing, it will work fine, just bigger ripple \$\endgroup\$
    – Lazyboy
    Commented May 8, 2018 at 8:04

1 Answer 1

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You set the parallel resistance on the inductors to have the same value as the series resistance, which effectively fully dampens them (more like turning them into slightly inductive resistors). The parallel resistance should be at least k\$\Omega\$ in value, if not tens or more. If you remove those values, everything works.

Also, the parallel cap at the input does exactly nothing, unless you set Rser to the source, or cap, but then you can simply specify the source to be 7 Rser=10m Cpar=4.7u, and delete the cap.

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    \$\begingroup\$ Sir, you are a lifesaver! If you ever pass throu Slovenia or Croatia, you're getting a beer from me! \$\endgroup\$
    – Lazyboy
    Commented May 8, 2018 at 8:12
  • \$\begingroup\$ @Lazyboy Well, I'll certainly remember that. :-) \$\endgroup\$
    – a concerned citizen
    Commented May 8, 2018 at 8:17

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