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I have tried to make LTSpice of step down DC-DC converter, however I cannot get it to work. I suspect the schematic is good however either LTSpice model is not correct or I made some critical mistake.

Models used are: TL494: https://www.mkdynamics.net/current_projects/current_projects_electronics_hacking_TL494_LTSpice_model.html

IRS21271 (converted from pspice): https://www.infineon.com/cms/en/product/power/gate-driver-ics/irs21271s/?tab=~%27simulation_models#!designsupport

Here is the schematic:

enter image description here

Now I cannot get it to stabilize at 12 V as it's supposed to. MOSFET driver seems to be working (blue input, green output):

enter image description here

Output seems to "stabilize" but at a way lower voltage than expected:

enter image description here

What am I doing wrong?

Here is the entire schematic: https://hastebin.skyra.pw/xosaliyexu.sql

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    \$\begingroup\$ High-side driver config looks wrong. \$\endgroup\$ Commented Nov 3, 2023 at 6:16

1 Answer 1

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You are using an N channel MOSFET and that requires a driver that is boot-strapped: -

enter image description here

Unfortunately, you don't appear to have implemented boot-strapping correctly. For instance, consider this circuit taken from the data sheet: -

enter image description here

I've highlighted Vs because this needs to connect to the source of the MOSFET to achieve proper boot-strapping of the gate driver. You have it connected to 0 volts and this inevitably means that the gate of the power MOSFET will only be driven to 12 volts.

Given that you require a 12 volt output, you need the gate to be driven to something like 24 volts to adequately turn-on the MOSFET. Proper boot-strapping ensures this.

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  • \$\begingroup\$ Indeed you are correct however with that configuration, ltspice does not want to run at all, takes like 10ns per second making it extremely slow \$\endgroup\$
    – Kaminari
    Commented Nov 3, 2023 at 16:14
  • \$\begingroup\$ @Kaminari sounds like a new issue to me; we don't like to escalate new unrelated problems onto the original question so, my advice is this: check what the maximum time step is that LTspice is using and, if that doesn't solve the problem (by making it bigger; maybe 100 ns), ask a new question and, if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something relating to your original question, then leave a comment to request further clarification. \$\endgroup\$
    – Andy aka
    Commented Nov 3, 2023 at 16:29
  • \$\begingroup\$ Not sure what to do to be honest because i tried many many things to get this circuit to working, should i just edit main question? \$\endgroup\$
    – Kaminari
    Commented Nov 3, 2023 at 19:43
  • \$\begingroup\$ No, the new problem requires a new question and, raising a new question opens things up to the whole community @Kaminari \$\endgroup\$
    – Andy aka
    Commented Nov 3, 2023 at 19:48
  • \$\begingroup\$ Accepting this answer then and posting new question \$\endgroup\$
    – Kaminari
    Commented Nov 3, 2023 at 20:21

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