Guidelines for switching N-channel JFETs to P-channel JFETs (and vica versa)? - diyAudio
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Old 21st January 2011, 03:08 PM   #1
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Default Guidelines for switching N-channel JFETs to P-channel JFETs (and vica versa)?

Couldn't find anything in the search so I though I'd ask in a thread: I'm wanting to use a P-chan. JFET instead of a N-chan. JFET as I'm trying to incorporate bits and pieces with different grounding for what the original diagram says, what would be the best way of going about working out and implementing this?
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Old 21st January 2011, 03:26 PM   #2
DF96 is offline DF96  England
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Just turn the whole circuit upside down?
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Old 21st January 2011, 06:41 PM   #3
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So everything in line with the drain is now attached to the source and vica versa?
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Old 22nd January 2011, 07:24 AM   #4
alexcp is offline alexcp  United States
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No, that is not what DF96 refers to. Better get an N-channel JFET as specified in the schematic; otherwise, your schematic is likely to end up not working.
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Old 22nd January 2011, 09:39 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by DF96 View Post
Just turn the whole circuit upside down?
means turn the schematic top to bottom.
Re-label the +ve supply which is at the bottom as a -ve supply.
Swap all transistors for their sisters, i.e. Nch becomes Pch NPN becomes PNP, Pch becomes Nch, PNP becomes NPN.
check and re-orient all polar semiconductors, eg. diodes, zeners, leds etc.

But since you misunderstood the first instruction then I too am inclined to agree with Alex. Don't.

Swap your Pch jFETs to Nch jFETs, you might negotiate 50 to 100% extra devices.
Or hold your stock and wait till a circuit that needs both Nch & Pch jFETs appeals to you.
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Last edited by AndrewT; 22nd January 2011 at 09:42 AM.
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Old 22nd January 2011, 01:04 PM   #6
DF96 is offline DF96  England
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Electrolytics too.

Alternatively, if the JFET is being used as a gate or variable resistor it might be possible to just invert part of the circuit. To do this successfully you would have sufficient knowledge that you probably would not have needed to ask the question.
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Old 22nd January 2011, 01:23 PM   #7
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Haha it's not amazingly complicated and I think it can be done for one particular thing I'm trying to do, this is the schematic:
Click the image to open in full size.
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Old 22nd January 2011, 01:38 PM   #8
AndrewT is offline AndrewT  Scotland
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that is an indicator to tell the operator that "effects" is switched ON.
It does not handle audio signal.
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Old 22nd January 2011, 05:35 PM   #9
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Of course but the ground is positive for what I'm trying to incorporate it in to, I take it that I don't just copy that circuit with but with the polarities reversed?
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Old 24th January 2011, 06:22 PM   #10
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I'll just fiddle with it in a circuit simulator and post the results...
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