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For an N-channel JFET transistor, current moves from drain to source. I've read that a P-channel JFET works similarly, but with the voltages reversed. Does this mean that its current travels from source to drain instead?

(The gate current can be neglected)

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  • \$\begingroup\$ jfets work in both direction of current for any one device. This because you can apply ac signals to the drain and this results in an ac current controlled by the gate. In more conventional circuits source is more positive than drain for a p channel device hence current flows from s to d. \$\endgroup\$
    – Andy aka
    Oct 29, 2013 at 22:50
  • \$\begingroup\$ Andy's already answered your question here: electronics.stackexchange.com/questions/86323/… Note the direction of current in Figure 1. \$\endgroup\$ Oct 30, 2013 at 2:13
  • \$\begingroup\$ @AlfredCentauri - thanks I knew that answer was somewhere!! \$\endgroup\$
    – Andy aka
    Oct 30, 2013 at 9:56

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This can be confusing - it's not entirely consistent naming.

I'm sure you've read else where and even on this site "don't worry if it's holes or electrons - the convention is positive charge flowing from a positive voltage to a more negative voltage to define +'ve current flow"

Or

" a negative charge flowing in the opposite direction equals positive current flow - the two signs cancel and you end up with positive charge flowing in a positive direction"

except ...

Then why does a nfet have a source that is on the -'ve rail and a drain that is at higher voltage? after all the "source" should be considered the the circuits above it "sourcing positive current and it drains the positive current into the drain. It would be consistent then.

So the short answer is, all those saying are true with respect to current, but device polarity is important to functionality and manufacturing. If you are connecting complementary polarity devices (P & N) in the same substrate you DO need to think about whether the device works with Electrons or with Holes or you'll mess up.

The easiest way to remember this is:

  • an N -type device needs a source of negative charge connected to it's Source - the negative rail.

  • a P type device needs a source of positive charge connected to it's Source - the positive rail.

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