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I just started learning circuit simulation using LTspice. I want to try a basic circuit such as buck converter for practice. I looked online for formulas to find the values of the required components, but none of the websites really specify which MOSFET they used. I looked through the list of PMOS and NMOS and I don't really have any idea which MOSFET is suitable and which MOSFET is not.

For example, if I wanted to build a 12V-5V buck converter, which MOSFET should I use?

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    \$\begingroup\$ This is a very broad question as it is going to depend heavily on your requirements. One oversimplified generic answer is: "the one with the lowest Rds(on) and gate charge you can get by without burning up the part". If you're just starting out and the tutorials don't give you a specific MOSFET, I would actually start by using the voltage controlled switch element (sw symbol) in LTspice. Then, once you get going and understand the operation of the circuit better, you can swap it out for an actual MOSFET. \$\endgroup\$
    – Ste Kulov
    Commented Mar 21, 2023 at 6:27
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    \$\begingroup\$ Also selecting a part in LTspice is irrelevant. You must select actually obtainable parts at your distributor. \$\endgroup\$
    – tobalt
    Commented Mar 21, 2023 at 6:29
  • \$\begingroup\$ So the best way to decide which mosfet to use is by checking the availability of the mosfet and reading the datasheet? If the market available mosfet is not on ltspice then I should choose another mosfet with similar specification? \$\endgroup\$
    – Jeremy
    Commented Mar 21, 2023 at 6:47
  • \$\begingroup\$ Yes you can choose one with similar specs, or place your own .model line with the specs from the datasheet. Btw, good distributors have powerful parametric search functions, so you have to look into datasheets only as confirmation. \$\endgroup\$
    – tobalt
    Commented Mar 21, 2023 at 7:19
  • \$\begingroup\$ The author of LTspice used to say (when he toured the world giving tutorials) that for switch-mode power supply applications, if the MOSFET you want to use isn't in the built-in library you should just pick an existing one with a similar Rds(on) and gate charge. \$\endgroup\$
    – Ste Kulov
    Commented Mar 21, 2023 at 17:11

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For example, if I wanted to build a 12V-5V buck converter, which MOSFET should I use?

Based on the information you have provided it could be a MOSFET like any of these: -

enter image description here

Image from Wiki - Small-outline transistor.

In other words a precise selection depends on other factors that you haven't provided. These are: -

  • Input voltage range
  • Load current maximum
  • Desired switching frequency
  • Maximum output ripple voltage

How do I decide which MOSFET to use in LTspice?

So, as Ste Kulov said in the first comment under the question, start by using a voltage controlled switch in your simulation: -

enter image description here

Image taken from this question and answer. Basically the voltage controlled switch is an ideal MOSFET and, of course, your simulation won't burn so, it's a good choice.

And, that choice will allow you to simulate what you need and give you the answers to the bulleted points I mentioned above.

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