EMRFD Message Archive 14133
Message Date From Subject 14133 2017-07-03 13:55:14 rcbuckiii J310 Source and Drain Swap If I open the data sheet for the On Semiconductor (or Fairchild) MMBFJ310 on the first page it says the drain and source are interchangeable. If I open the data sheet for the J310, it doesn't mention drain and source as being interchangeable. However, maybe they are because the Hycas IF amplifier schematic doesn't label drain or source. To assume drain is on top and source is on bottom is probably not a good idea.
I searched online and there seem to be differing opinions. Some people say yes and others say no. Wikipedia says if the device symbol for the gate is centered between the drain and source, this would indicate they are interchangeable.
I read Wes' JFET 101 tutorial and he doesn't mention anything about interchangeability. He does say to look at the silicon slab as being a resistor. This would indicate drain and source are interchangeable.
14134 2017-07-03 15:10:32 Chris Trask Re: J310 Source and Drain Swap >Yes, they are interchangeable as the die is symmetrical, and it doesn't matter who manufactured it
>If I open the data sheet for the On Semiconductor (or Fairchild)
>MMBFJ310 on the first page it says the drain and source are
>interchangeable. If I open the data sheet for the J310, it doesn't
>mention drain and source as being interchangeable. However, maybe they
>are because the Hycas IF amplifier schematic doesn't label drain or
>source. To assume drain is on top and source is on bottom is probably
>not a good idea.
>I searched online and there seem to be differing opinions. Some people
>say yes and others say no. Wikipedia says if the device symbol for the
>gate is centered between the drain and source, this would indicate they
>I read Wes' JFET 101 tutorial and he doesn't mention anything about
>interchangeability. He does say to look at the silicon slab as being a
>resistor. This would indicate drain and source are interchangeable.
When the going gets weird, the weird turn pro
- Hunter S. Thompson
14135 2017-07-03 16:01:39 rcbuckiii Re: J310 Source and Drain Swap Thanks Chris. I was laying out a circuit board and it is easier when the drain and source are interchangeable.
14137 2017-07-04 03:36:42 i7swx Re: J310 Source and Drain Swap Hi Ray,
some friends gave you the right answer.
Kenwood used j<310 in some of their transceivers and in some equiment were soldered "reversed". Some people discovered this "mistake" and replaced thise with ne J310 with the "right" connections and others reversed them to the right position but no improuvement discovere as are bi-directiona. I do not remember if the rtx were TS930 or/and TS940.
14138 2017-07-04 12:02:46 rcbuckiii Re: J310 Source and Drain Swap Thanks Gian. That is interesting to know. I have a TS820S but I don't know off hand if it used J310s or not.
14139 2017-07-05 03:57:58 i7swx Re: J310 Source and Drain Swap Hi Ray,
TS820 has no JFETs.
14140 2017-07-05 12:46:24 pa_lender Re: J310 Source and Drain Swap -- Other FETs? Hi Folks
1) Does this follow for *any* junction FET or just the J310 (and maybe the J30x series)?.
2) In schematics for grounded gate amplifiers, the drain and source are rarely labeled, though here's one that is: http://www.qsl.net/wn5y/ra01042.htm . It's very nice that a J310 would often be used here and it doesn't matter.
When it *does* matter in a grounded gate amp, does the drain always connect to +V, as here?
Thanks in advance...
-- Paul AD0HQ
14141 2017-07-05 19:22:28 James Duffey Re: J310 Source and Drain Swap -- Other FETs? The old Siliconix data books had die photos or diagrams in the back which were referred to the data sheets for each particular FET. The J310 die is clearly symmetrical, that is, the drain and source are symmetrical. So you can switch them around with no problem. I think that the J309 and J308 have the same die diagram. I think that this is also true for the MPF102 and 2N4416 JFETs. If you have questions about a specific JFET, try to get a hold of the old Siliconix JFET databook. I think there may be a copy on the web. If you have question on a specific JFET, I can try to find my old Siliconix databooks and look it up for you. As I have recently cleaned out my office, this is probably not an easy chore.
This symmetry is not true of all JFETs though. There are advantages to an asymmetrical drain-source channel, but for most ham radio applications the J310 or metal cased U310 are about as good as it gets for Silicon JFETs. Lower noise applications are better suited for GaAs or other materials. One advantage of the asymmetrical drain gate is that one can control which way the excess channel charge goes when switched on or off, which has some noise advantages. To first order, the square root of the excess charge shows up as additional noise, so if one can reduce this one can reduce the noise.
I hope this helps. - Duffey KK6MC
Cedar Crest NM
14142 2017-07-06 04:01:16 i7swx Re: J310 Source and Drain Swap -- Other FETs? Hi Paul,
James answered to your questions.
I had a Siliconx book and also a National one regarding FETs. There were a picture of dices and also the original dice for the different products selection.
Ray and all, I forgot to mention that the JFET used by Kenwood was the japanese 2SK125 similar to the J310 and used on the TS930 and 940, sorry for reporting the J310.
14143 2017-07-06 09:23:15 lawrence_joy Re: J310 Source and Drain Swap Ray (and everyone else). The newer graphic symbol for a JFET draws the gate element in line with the source element, whether the device is symmetrical or not. Just like for a BJT there is no need to label the elements/terminals when drawing the JFET in this fashion. The IEC 60617 symbol(s) appear in IEEE 315A-1986 clause 184.108.40.206 for the N-channel JFET and clause 220.127.116.11 for the P-channel JFET. These "newer" symbols are over 30 years old.Years ago, even a decade or more ago, there was an article in QST for a UHF oscillator that used an unsymmetrical, high frequency FET. The article schematic showed the gate terminal centered between the drain and source terminals and no labeling of the terminals. In this case if you wired it up "backwards" it would not oscillate. The ARRL had feedback/correction to the schematic to indicate terminal identity. If they would have used the newer symbol there would have been no problem.73 de 9V1MI/WN8P, LarryARRL LM & MI Section TS