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I'm trying to design and build a simple ac/dc smps that outputs 5v dc and capable of 2 amps. I currently have it mostly designed using a nmos but the problem I'm running into now is how to get a pwm signal with 18V. Is there any advantage to using a PMOS or a NMOS or vice versa? I need to build this soon to stay on track for my project so any input is helpful! I was thinking of using a microcontroller to do the feedback but I understand that I will need a gate driver for it also. I'm not the strongest at programming so I am interested in seeing if there's any ic's or circuitry that I can design that will do the feedback for the pwm input for the gate of the mosfet. I imagine I would still need a gate driver for that option too. I appreciate the help.enter image description here

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  • \$\begingroup\$ Just a small note: output voltage won't be isolated from the mains. So you cannot touch anything that will be connected to it. \$\endgroup\$ – Chupacabras May 19 '18 at 5:47
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PMOS are more expensive to produce, they have grater Rdson than a copmlementary NMOS, therefore almost all SMPS are using NMOS, because of less generated heat, less size, less price. I don't know if there is a single pros for the PMOS.

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    \$\begingroup\$ PMOS devices do not need a gate voltage boost circuit in a positive power supply - that is their primary pro. \$\endgroup\$ – Peter Smith Sep 16 '15 at 8:58
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    \$\begingroup\$ Most modern SMPS ICs are using PMOS switches internally. For the same Rds_on a PMOS must be about 3x larger, this is caused by the lower mobility of holes which are the charge carriers in a PMOS. Yes a PMOS is larger and thus more expensive but for an NMOS switch a voltage boost is needed which also takes up chip area and/or adds external components. \$\endgroup\$ – Bimpelrekkie Sep 16 '15 at 14:55
  • \$\begingroup\$ If you want to learn and are an experimenter then try the "Roman Black " convertor its from iron curtain origions and its simple .You will have to tart up the design to make it reliable ,and you can adapt it to a mosfet .In fact you will have lots of fun. \$\endgroup\$ – Autistic Sep 25 '15 at 21:52
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Yes there is an advantage to using a PMOS, the driving circuit becomes much simpler. Although not concerning an SMPS but switching a load, my answer here might explain it to you.

There are many SMPS switching controllers, for example here Also have a look at the datasheet of the TL494, it is an excellent starting point.

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