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When are P channel mosfets used instead of N channel mosfets? When should you NOT use a P channel mosfet instead of a N channel mosfet, and vice versa? When should you use a Jfet?

I just want to get a good comparison going between the different channel mosfets.

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  • \$\begingroup\$ Seeing my answer has been emsaculated: You would, in my opinion, and I claim to speak for nobody else, gain a lot by using a good search engine to research the subject before asking such fundamental questions here. If you have done that you should say so, so that people answering have some idea of your learning ability and can tailor answers accordingly. \$\endgroup\$ – Russell McMahon Oct 10 '11 at 17:32
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JFETs are rarely used (hard to find nowadays) but do have a place in high-speed analog circuits where they can be used as current sources or signal buffers.

Otherwise, a similar question has been asked before: Switching DC with MOSFET: p-Channel or n-Channel; Low Side Load or High Side Load?

I wrote a blog post about the different topologies.

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A P Channel MOSFET tends to be used to connect a high level "rail" to a load.
You should use it when this best describes the circuit condition.
It's turn on signals are negative relative to the rail it is connected to.

An N Channel MOSFET tends to be used to connect ground to a load which is connected to a higher +ve voltage.
You should use it when this best describes the circuit condition.
It's turn on signals are positive relative to the rail it is connected to.

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    \$\begingroup\$ The goal of Stack-exchange is to be the source that google returns. RTFM answers(read the freakin manual) are not acceptable here, and telling someone to google it is considered just that. You are an expert, bring some of that great information over and leave references, you can condense it to the delicious meat of the solution and allow all of those other sites to be references. Your question has been edited to remove the google it parts of the answer. \$\endgroup\$ – Kortuk Oct 10 '11 at 15:42
  • \$\begingroup\$ @Kortuk - I am fully aware of the RTFM / LMGTFY perspective taken by the site. BUT there is a stage where that is the best answer. I NEVER just say "use Google". I gave him a lead, answered the question better than many might anyway and said that there were so many hits on Google that he really really really should look at some. That was very good advice and failing to give it to some people is insanity. \$\endgroup\$ – Russell McMahon Oct 10 '11 at 16:05
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    \$\begingroup\$ @RussellMcMahon - Sorry it's early. You're right, there is a lot of information on the Internet. One of our goals is to make this information digestible to someone with a specific question. Answers like "Here are the results of a Google search" here, this one, and this one provide lots of information, but are hard to digest. \$\endgroup\$ – Kevin Vermeer Oct 10 '11 at 16:19
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    \$\begingroup\$ Please see this article by Jon Skeet for more about writing good answers. Your primary goal should be to answer the question helpfully, not to provide information to be interpreted. Granted, that's difficult for questions like this one, but better questions can get better answers. \$\endgroup\$ – Kevin Vermeer Oct 10 '11 at 16:22
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    \$\begingroup\$ @RussellMcMahon - The low-quality questions are not something that you control. Your answers are something you control. Of course, you're welcome to flag, vote to close, edit, and refer to electronics.stackexchange.com/qestions/how-to-ask and other resources. We want high quality questions! \$\endgroup\$ – Kevin Vermeer Oct 10 '11 at 19:53

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