# JFET with fwd xfer admittance >30mmhos?

J

#### Joerg

Jan 1, 1970
0
Just curious, ran into this a few times: Is there a JFET in the J310
price category with a forward transfer admittance in excess of 30mmhos?
Doesn't matter whether N or P.

The BF862 fits the bill very nicely at 45mmhos but it costs around 15c,
versus 6c or so for the J310. Looking for a partially free lunch here
....

L

#### legg

Jan 1, 1970
0
Just curious, ran into this a few times: Is there a JFET in the J310
price category with a forward transfer admittance in excess of 30mmhos?
Doesn't matter whether N or P.

The BF862 fits the bill very nicely at 45mmhos but it costs around 15c,
versus 6c or so for the J310. Looking for a partially free lunch here
...

Although the 2N4391 switch was never speced for gfs, which is what I
hope you're refering to on an older datasheet, MPS4391 developed for
the same purpose was 20mS typ. Might be worth looking at the MMBF4391
switches, for function.

I only recall one or two that were higher (BSV39 70mS typ) without
actually being a high power device (U244 U266), though Teledyne ($) did quite a few above 20mS (2N6453). RL J #### Joerg Jan 1, 1970 0 legg said: Although the 2N4391 switch was never speced for gfs, which is what I hope you're refering to on an older datasheet, MPS4391 developed for the same purpose was 20mS typ. Might be worth looking at the MMBF4391 switches, for function. I only recall one or two that were higher (BSV39 70mS typ) without actually being a high power device (U244 U266), though Teledyne ($)
did quite a few above 20mS (2N6453).

They have all gone to lalaland. The MMBF4391 is still made by ON and
Fairchild but hard to get. And it's still <20mmhos.

L

#### legg

Jan 1, 1970
0
They have all gone to lalaland. The MMBF4391 is still made by ON and
Fairchild but hard to get. And it's still <20mmhos.

Did you confirm the gfs of an xx4391 sample? I see that the ON
datasheet shows it still climbing at 30mA, with the minimum Idss for
the part exceeding 50mA. Same might be said for the MMBFJ310, although
its minimum Idss is half that. Just curious.

Is it intended to work at VHF, or is this just an incidental
characteristic of the BF862?

Should have thought, that with cost being important, the .104 price
might have justified the effort. This would likely change, on serious
inquiry, for a multiply-sourced part that hasn't recently been
ordered. (BF862 is .16 from the same vendor's single source). The
PMBFJ310 is .095 from the same vendor, for reference.

RL

J

#### Joerg

Jan 1, 1970
0
legg said:
Did you confirm the gfs of an xx4391 sample? I see that the ON
datasheet shows it still climbing at 30mA, with the minimum Idss for
the part exceeding 50mA. Same might be said for the MMBFJ310, although
its minimum Idss is half that. Just curious.

I haven't, don't have one here. But in an oscillator scenario it would
become quite toasty and you'd have to load it down at the output.

Is it intended to work at VHF, or is this just an incidental
characteristic of the BF862?

Most of them are like that. For me it rarely matters, you just have to
make sure they don't "sing" up there. Else the FCC sends the goons out ;-)

Should have thought, that with cost being important, the .104 price
might have justified the effort. This would likely change, on serious
inquiry, for a multiply-sourced part that hasn't recently been
ordered. (BF862 is .16 from the same vendor's single source). The
PMBFJ310 is .095 from the same vendor, for reference.

Digikey? There they'll go to around 7c for 50k or larger qties.

L

#### legg

Jan 1, 1970
0
I haven't, don't have one here. But in an oscillator scenario it would
become quite toasty and you'd have to load it down at the output.

Most of them are like that. For me it rarely matters, you just have to
make sure they don't "sing" up there. Else the FCC sends the goons out ;-)

Digikey? There they'll go to around 7c for 50k or larger qties.

Belatedly, try 2SK536 from Sanyo, if you can find a distributor.

RL

J

#### Joerg

Jan 1, 1970
0
legg said:
Belatedly, try 2SK536 from Sanyo, if you can find a distributor.

There are a few mouth-watering JFETs from Japan but many of them have
become boutique parts. My clients would have me flogged

L

#### legg

Jan 1, 1970
0
There are a few mouth-watering JFETs from Japan but many of them have
become boutique parts. My clients would have me flogged

This isn't one of them, but you have to buy them new through a Sanyo
rep. They've been in production long enough to be available in smaller
quantities from brokers.

On closer inspection, it's also not a JFET, but NMOS.

RL

J

#### Joerg

Jan 1, 1970
0
legg said:
This isn't one of them, but you have to buy them new through a Sanyo
rep. They've been in production long enough to be available in smaller
quantities from brokers.

On closer inspection, it's also not a JFET, but NMOS.

That wouldn't work in really low voltage envoironments. Often one needs
a JFET that can reliably start and deliver some juice as an oscillator
at a few hundred millivolts.

Replies
5
Views
441
Replies
15
Views
2K
Replies
2
Views
1K
Replies
56
Views
3K
Replies
12
Views
800