> "bitrex" <bitrex@de.lete.earthlink.net> wrote in message
> news:YyKQA.72159$De7.40392@fx24.iad...
>> BJTs are really more like voltage controlled current sources with a
>> pathology than current controlled current sources
>>
>
> And with much more gain than MOSFETs!
>
> I like to think of low-Vce(sat) transistors as "MOSFETs with 5x more
> gain but a really leaky gate". They have a reasonably linear (including
> 3rd quadrant) "Rce(on)", too.
>
> "Vbe(th)" is also way more repeatable. I was testing almost a hundred
> boards, recently, and measured a current-limited output on each of them
> as part of the test spec. The design is guard-banded, so the current
> limit is high enough never to matter in normal operation, while it's
> also low enough to dissipate a safe amount of power when shorted.
> Despite the wide design tolerance, they all measured within 0.3% of each
> other. (Evidently, room temperature was pretty stable between those
> days of testing.)
>
> Tim
>
Ya, I suppose if you could design a transconductance physics box with an
exponential law instead of square that also had a pretty well-defined
"gate" threshold of 0.6 volts and drew no "gate" current, there would be
little reason to use anything else assuming similar noise performance
over a similar bandwidth.
I think (x)HEMTs come pretty close, sadly they are not literally a dime
a dozen and likely never will be.
Reply by Jan Panteltje●May 11, 20172017-05-11
On a sunny day (Wed, 10 May 2017 11:30:14 -0400) it happened bitrex
<bitrex@de.lete.earthlink.net> wrote in <amGQA.20524$rp2.9505@fx31.iad>:
>On 05/10/2017 10:42 AM, Jan Panteltje wrote:
>
>>>> I exected a circuit diagram ;-(
>>>
>>> Sorry, that's too valuable to give away. I will say: drive the gates
>>> hard and ignore the data sheets.
>>
>> Let me guess, you used an ethernet transformer...?
>
>Nah nah it was an _isdn_ xfrmr. That's the good shit
>
>>
>> Maybe some science field, was just reading CERN started a new linear accelerator:
>> https://home.cern/about/updates/2017/05/brand-new-linear-accelerator-cern
>>
>
>Where's Famous Chef Pante?
Na, was in the kitchen just now baking mushrooms...
MY opinion on this, and actually last night there was, on cable here,
a professor giving college about CERN comparing it to a super microscope.
You know ever higher energies needed to take a picture of ever smaller things.
But if you ask me, I did say:
'Do you really expect to get a deeper insight into the Tesla autopilot software
by driving those into each other at 1000 km/h?'
So..
Reply by Jan Panteltje●May 11, 20172017-05-11
On a sunny day (Wed, 10 May 2017 16:16:56 -0400) it happened bitrex
<bitrex@de.lete.earthlink.net> wrote in <YyKQA.72159$De7.40392@fx24.iad>:
>BJTs are really more like voltage controlled current sources with a
>pathology than current controlled current sources
Well, maybe you misread the label, and it was a FET...
:-)
Reply by Tim Williams●May 10, 20172017-05-10
"bitrex" <bitrex@de.lete.earthlink.net> wrote in message
news:YyKQA.72159$De7.40392@fx24.iad...
> BJTs are really more like voltage controlled current sources with a
> pathology than current controlled current sources
>
And with much more gain than MOSFETs!
I like to think of low-Vce(sat) transistors as "MOSFETs with 5x more gain
but a really leaky gate". They have a reasonably linear (including 3rd
quadrant) "Rce(on)", too.
"Vbe(th)" is also way more repeatable. I was testing almost a hundred
boards, recently, and measured a current-limited output on each of them as
part of the test spec. The design is guard-banded, so the current limit is
high enough never to matter in normal operation, while it's also low enough
to dissipate a safe amount of power when shorted. Despite the wide design
tolerance, they all measured within 0.3% of each other. (Evidently, room
temperature was pretty stable between those days of testing.)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
Reply by bitrex●May 10, 20172017-05-10
On 05/10/2017 04:49 PM, Jim Thompson wrote:
>> BJTs are really more like voltage controlled current sources with a
>> pathology than current controlled current sources
>
> Bwahahahahahaha >:-}
>
> ...Jim Thompson
There have been analog designers with a lot more experience than I have
that've said much the same thing.
The Ebers-Moll equation relating Ie to Vbe says nothing about Ie
dependence on base current.
Gummel-Poon charge-controlled model is useless outside of computer
simulation
Reply by Jim Thompson●May 10, 20172017-05-10
On Wed, 10 May 2017 16:16:56 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:
>On 05/10/2017 10:56 AM, John Larkin wrote:
>> On Wed, 10 May 2017 08:05:51 GMT, Jan Panteltje
>> <pNa0nStpealmtje@yahoo.com> wrote:
>>
>>> On a sunny day (Tue, 09 May 2017 16:32:11 -0700) it happened John Larkin
>>> <jjlarkin@highland_snip_technology.com> wrote in
>>> <qak4hc5lre1ohrf47f734bvk2qqvfl634b@4ax.com>:
>>>
>>>> I rarely use bipolar transistors any more.
>>>
>>> Maybe for high end stuff like you are making,
>>> but for many down to earth things they are very useful,
>>> bipolars are basically current amplifiers.
>>> MOSFETS voltage to current converters.
>>> Both have their field of application where they are best.
>>> And there are some nice RF ones too.
>>
>> We trend to use PHEMTS for fast stuff. The place where we use still
>> bipolars is in positive current sources, because mosfets have too much
>> capacitance and nobody makes p-channel phemts.
>>
>> Base current sucks. I designed a fast currrent source with base
>> current correction, but it's kinda complex.
>>
>
>BJTs are really more like voltage controlled current sources with a
>pathology than current controlled current sources
Bwahahahahahaha >:-}
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie
Reply by bitrex●May 10, 20172017-05-10
On 05/10/2017 10:56 AM, John Larkin wrote:
> On Wed, 10 May 2017 08:05:51 GMT, Jan Panteltje
> <pNa0nStpealmtje@yahoo.com> wrote:
>
>> On a sunny day (Tue, 09 May 2017 16:32:11 -0700) it happened John Larkin
>> <jjlarkin@highland_snip_technology.com> wrote in
>> <qak4hc5lre1ohrf47f734bvk2qqvfl634b@4ax.com>:
>>
>>> I rarely use bipolar transistors any more.
>>
>> Maybe for high end stuff like you are making,
>> but for many down to earth things they are very useful,
>> bipolars are basically current amplifiers.
>> MOSFETS voltage to current converters.
>> Both have their field of application where they are best.
>> And there are some nice RF ones too.
>
> We trend to use PHEMTS for fast stuff. The place where we use still
> bipolars is in positive current sources, because mosfets have too much
> capacitance and nobody makes p-channel phemts.
>
> Base current sucks. I designed a fast currrent source with base
> current correction, but it's kinda complex.
>
BJTs are really more like voltage controlled current sources with a
pathology than current controlled current sources
Reply by bitrex●May 10, 20172017-05-10
On 05/10/2017 12:11 PM, John Larkin wrote:
> On Wed, 10 May 2017 11:30:14 -0400, bitrex
> <bitrex@de.lete.earthlink.net> wrote:
>
>> On 05/10/2017 10:42 AM, Jan Panteltje wrote:
>>
>>>>> I exected a circuit diagram ;-(
>>>>
>>>> Sorry, that's too valuable to give away. I will say: drive the gates
>>>> hard and ignore the data sheets.
>>>
>>> Let me guess, you used an ethernet transformer...?
>>
>> Nah nah it was an _isdn_ xfrmr. That's the good shit
>
> ISDN transformers are really cool; I've used lots of them (over 20K!)
> in power supplies and such. My favorite part is 1:1:2:2, which is
> pretty versatile. But I use home-made transmission-line xfmrs for big
> fast pulses.
>
> Is ISDN still alive? "It Still Does Nothing"
I know it was "Big in Japan" for a while...
<https://www.youtube.com/watch?v=DdWZKb659K0>
I think it's still used by some businesses for POS applications and
stuff. The wiki says Verizon no longer offers it in the Northeast as of 2013
Reply by John Larkin●May 10, 20172017-05-10
On Wed, 10 May 2017 12:37:04 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>On 05/10/2017 12:27 PM, John Larkin wrote:
>> On Wed, 10 May 2017 11:20:19 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> On 05/10/2017 10:56 AM, John Larkin wrote:
>>>> On Wed, 10 May 2017 08:05:51 GMT, Jan Panteltje
>>>> <pNa0nStpealmtje@yahoo.com> wrote:
>>>>
>>>>> On a sunny day (Tue, 09 May 2017 16:32:11 -0700) it happened John Larkin
>>>>> <jjlarkin@highland_snip_technology.com> wrote in
>>>>> <qak4hc5lre1ohrf47f734bvk2qqvfl634b@4ax.com>:
>>>>>
>>>>>> I rarely use bipolar transistors any more.
>>>>>
>>>>> Maybe for high end stuff like you are making,
>>>>> but for many down to earth things they are very useful,
>>>>> bipolars are basically current amplifiers.
>>>>> MOSFETS voltage to current converters.
>>>>> Both have their field of application where they are best.
>>>>> And there are some nice RF ones too.
>>>>
>>>> We trend to use PHEMTS for fast stuff. The place where we use still
>>>> bipolars is in positive current sources, because mosfets have too much
>>>> capacitance and nobody makes p-channel phemts.
>>>>
>>>> Base current sucks. I designed a fast currrent source with base
>>>> current correction, but it's kinda complex.
>>>
>>> I mostly use BJTs as transconductance devices, and their nice repeatable
>>> turn-on is a big plus. They're also much better in low-voltage analogue
>>> stuff for the same reason. Besides being much, much quieter.
>>>
>>> PNPs are good for positive-to-negative level shifting, too.
>>>
>>> Those SiGe:C devices (BFP640/650) are magic--high beta, low noise,
>>> effectively infinite VAF, and bandwidth that goes on forever. As you
>>> pointed out some time back, they don't switch as fast as pHEMTs that are
>>> seemingly slower. That one-diode sampler I did with ChesterW last year
>>> originally used a BFP640FESD, which produced a 200-ps sampler. Swapping
>>> it out for an ATF55143 got us down to 100 ps, but cost an extra 45 cents
>>> ($0.67 vs $0.22).
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> The problem with fast bipolars, especially PNPs, is that they keep
>> getting EOL'd.
>>
>>
>
>I'm planning to get a few reels for insurance pretty soon. BFP640s are
>too useful to lose, and they're only 20 cents or so--just like a BF862.
>
>A couple of dollar's worth of fancy transistors can let me build a very
>swoopy box that sells (hopefully!) for $2k-ish.
>
>Cheers
>
>Phil Hobbs
We both sell IP, soldered to PC boards.
One of our customers wants to audit our parts cost to see if we're
making too much money. We declined.
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Reply by Phil Hobbs●May 10, 20172017-05-10
On 05/10/2017 12:27 PM, John Larkin wrote:
> On Wed, 10 May 2017 11:20:19 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 05/10/2017 10:56 AM, John Larkin wrote:
>>> On Wed, 10 May 2017 08:05:51 GMT, Jan Panteltje
>>> <pNa0nStpealmtje@yahoo.com> wrote:
>>>
>>>> On a sunny day (Tue, 09 May 2017 16:32:11 -0700) it happened John Larkin
>>>> <jjlarkin@highland_snip_technology.com> wrote in
>>>> <qak4hc5lre1ohrf47f734bvk2qqvfl634b@4ax.com>:
>>>>
>>>>> I rarely use bipolar transistors any more.
>>>>
>>>> Maybe for high end stuff like you are making,
>>>> but for many down to earth things they are very useful,
>>>> bipolars are basically current amplifiers.
>>>> MOSFETS voltage to current converters.
>>>> Both have their field of application where they are best.
>>>> And there are some nice RF ones too.
>>>
>>> We trend to use PHEMTS for fast stuff. The place where we use still
>>> bipolars is in positive current sources, because mosfets have too much
>>> capacitance and nobody makes p-channel phemts.
>>>
>>> Base current sucks. I designed a fast currrent source with base
>>> current correction, but it's kinda complex.
>>
>> I mostly use BJTs as transconductance devices, and their nice repeatable
>> turn-on is a big plus. They're also much better in low-voltage analogue
>> stuff for the same reason. Besides being much, much quieter.
>>
>> PNPs are good for positive-to-negative level shifting, too.
>>
>> Those SiGe:C devices (BFP640/650) are magic--high beta, low noise,
>> effectively infinite VAF, and bandwidth that goes on forever. As you
>> pointed out some time back, they don't switch as fast as pHEMTs that are
>> seemingly slower. That one-diode sampler I did with ChesterW last year
>> originally used a BFP640FESD, which produced a 200-ps sampler. Swapping
>> it out for an ATF55143 got us down to 100 ps, but cost an extra 45 cents
>> ($0.67 vs $0.22).
>>
>> Cheers
>>
>> Phil Hobbs
>
> The problem with fast bipolars, especially PNPs, is that they keep
> getting EOL'd.
>
>
I'm planning to get a few reels for insurance pretty soon. BFP640s are
too useful to lose, and they're only 20 cents or so--just like a BF862.
A couple of dollar's worth of fancy transistors can let me build a very
swoopy box that sells (hopefully!) for $2k-ish.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net