Reply by John Larkin December 9, 20152015-12-09
On Wed, 09 Dec 2015 05:28:49 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Wed, 9 Dec 2015 01:51:53 -0800 (PST), the renowned >tabbypurr@gmail.com wrote: > >>On Wednesday, 9 December 2015 04:10:16 UTC, John Larkin wrote: >> >>> Thanks, but I don't need that precision, and we have the BCX70 in >>> stock. >>> >>> Putting more parts into stock is generally avoided. We have 6469 parts >>> already, 3.03 million pieces. >> >>Ouch. JIT. >> >> >>NT > >I think at one time JL said they had more than 100 types of LDO alone >in stock. > > >--sp
Yeah, too many voltage regulators. About 100, of all kinds, including switchers. Most of those 3e6 parts are resistors and caps on reels.
Reply by Phil Hobbs December 9, 20152015-12-09
On 12/08/2015 01:53 PM, John Larkin wrote:
> On 08 Dec 2015 11:22:12 GMT, Allan Herriman > <allanherriman@hotmail.com> wrote: > >> On Mon, 07 Dec 2015 11:47:48 -0800, John Larkin wrote: >> >>> I need a wimpy diode, with lots of forward drop at a few mA, to bias up >>> an e-phemt. Thought I'd try a small-geometry NPN transistor. >>> >>> https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/ >> BCX70_as_Diode.JPG >>> >>> Looks good. The b-e and b-c junctions look symmetric. >>> >>> The middle config looks like the classic 60 mV/decade-current, and the >>> others are maybe a little ohmic. We pay 2.4 cents each for these, so I >>> don't mind wasting the transistor action. >> >> >> I use a BAV199W if I want a high forward drop or vanishingly small >> reverse current. Vf is not very well constrained by worst case limits in >> the datasheet though. >> >> Allan > > If you want crazy low reverse current, consider the c-b junction of a > BFT25. > > https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/BFT25.JPG > > That reverse leakage was about at my measurement resolution limit. > >
I'm using one in that super low cost TIA (with the LM324). It's in parallel with a 200M feedback resistor, to give a logarithmic overrange indication. Your plot has the transistor in normal bias for the inverted configuration (collector negative), which probably helps the log conformance a fair amount. 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
Reply by Spehro Pefhany December 9, 20152015-12-09
On Wed, 9 Dec 2015 01:51:53 -0800 (PST), the renowned
tabbypurr@gmail.com wrote:

>On Wednesday, 9 December 2015 04:10:16 UTC, John Larkin wrote: > >> Thanks, but I don't need that precision, and we have the BCX70 in >> stock. >> >> Putting more parts into stock is generally avoided. We have 6469 parts >> already, 3.03 million pieces. > >Ouch. JIT. > > >NT
I think at one time JL said they had more than 100 types of LDO alone in stock. --sp -- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8 Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48
Reply by December 9, 20152015-12-09
On Wednesday, 9 December 2015 04:10:16 UTC, John Larkin  wrote:

> Thanks, but I don't need that precision, and we have the BCX70 in > stock. > > Putting more parts into stock is generally avoided. We have 6469 parts > already, 3.03 million pieces.
Ouch. JIT. NT
Reply by John Larkin December 9, 20152015-12-09
On Tue, 08 Dec 2015 14:31:08 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Tue, 8 Dec 2015 04:56:30 -0800 (PST), tabbypurr@gmail.com wrote: > >>On Tuesday, 8 December 2015 11:22:17 UTC, Allan Herriman wrote: >>> On Mon, 07 Dec 2015 11:47:48 -0800, John Larkin wrote: >>> >>> > I need a wimpy diode, with lots of forward drop at a few mA, to bias up >>> > an e-phemt. Thought I'd try a small-geometry NPN transistor. >>> > >>> > https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/ >>> BCX70_as_Diode.JPG >>> > >>> > Looks good. The b-e and b-c junctions look symmetric. >>> > >>> > The middle config looks like the classic 60 mV/decade-current, and the >>> > others are maybe a little ohmic. We pay 2.4 cents each for these, so I >>> > don't mind wasting the transistor action. >>> >>> >>> I use a BAV199W if I want a high forward drop or vanishingly small >>> reverse current. Vf is not very well constrained by worst case limits in >>> the datasheet though. >>> >>> Allan >> >>I've got a graph from who knows where that shows 1N458 0.8v @ 10mA. FWIW. >> >> >>NT > > >I think for exactly 800mV I'd be tempted to just slap an AP2127 down >there- SOT-23-5 and you get 800mV +/-2% with no additional parts (just >an output cap). Less than 10 cents in quantity, and it can be used in >other applications. Even has a shutdown input. > >
Thanks, but I don't need that precision, and we have the BCX70 in stock. Putting more parts into stock is generally avoided. We have 6469 parts already, 3.03 million pieces.
Reply by Martin Riddle December 8, 20152015-12-08
On Tue, 8 Dec 2015 22:52:08 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

>On 08/12/2015 08:08, John Larkin wrote: >> On Mon, 7 Dec 2015 12:49:17 -0800 (PST), tabbypurr@gmail.com wrote: >> >>> On Monday, 7 December 2015 20:33:47 UTC, John Larkin wrote: >>>> On Mon, 7 Dec 2015 12:04:08 -0800 (PST), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Monday, December 7, 2015 at 2:47:59 PM UTC-5, John Larkin wrote: >>>>>> I need a wimpy diode, with lots of forward drop at a few mA, to bias >>>>>> up an e-phemt. Thought I'd try a small-geometry NPN transistor. >>>>>> >>>>>> https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/BCX70_as_Diode.JPG >>>>>> >>>>>> Looks good. The b-e and b-c junctions look symmetric. >>>>>> >>>>>> The middle config looks like the classic 60 mV/decade-current, and the >>>>>> others are maybe a little ohmic. We pay 2.4 cents each for these, so I >>>>>> don't mind wasting the transistor action. >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> >>>>>> John Larkin Highland Technology, Inc >>>>>> picosecond timing precision measurement >>>>>> >>>>>> jlarkin att highlandtechnology dott com >>>>>> http://www.highlandtechnology.com >>>>> >>>>> An LED? or is that too much voltage? >>>>> >>>>> George H. >>>> >>>> I want about 0.8 volts, to be a little above the gate turn-on voltage >>>> of the enhancement phemt. It would be cool to see it glow, but a >>>> visible LED would be 1.8 volts or so. >>>> >>>> I have used LEDs as the voltage reference for simple current sources, >>>> where they are just right. >>> >>> Aren't 2 diodes cheaper? >>> >>> >>> NT >> >> The right LED at the right current will have a temperature coefficient >> that almost cancels the Vbe of a transistor. >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/Current_Sources/LED_Isrc_bb.JPG >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/Current_Sources/LED_Isrc_data.JPG >> >> Plus, it glows in the dark! >> >> > >In some companies there could be a risk that someone in Marketing will >change the LED colour to blue without asking you, because the blue LEDs >fitted under his car look so good. >
I find that Blue LED's create a blue fog of dispersed light vs. Green, amber or Red LED's. It's particularly annoying. Cheers
Reply by Spehro Pefhany December 8, 20152015-12-08
On Tue, 8 Dec 2015 04:56:30 -0800 (PST), tabbypurr@gmail.com wrote:

>On Tuesday, 8 December 2015 11:22:17 UTC, Allan Herriman wrote: >> On Mon, 07 Dec 2015 11:47:48 -0800, John Larkin wrote: >> >> > I need a wimpy diode, with lots of forward drop at a few mA, to bias up >> > an e-phemt. Thought I'd try a small-geometry NPN transistor. >> > >> > https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/ >> BCX70_as_Diode.JPG >> > >> > Looks good. The b-e and b-c junctions look symmetric. >> > >> > The middle config looks like the classic 60 mV/decade-current, and the >> > others are maybe a little ohmic. We pay 2.4 cents each for these, so I >> > don't mind wasting the transistor action. >> >> >> I use a BAV199W if I want a high forward drop or vanishingly small >> reverse current. Vf is not very well constrained by worst case limits in >> the datasheet though. >> >> Allan > >I've got a graph from who knows where that shows 1N458 0.8v @ 10mA. FWIW. > > >NT
I think for exactly 800mV I'd be tempted to just slap an AP2127 down there- SOT-23-5 and you get 800mV +/-2% with no additional parts (just an output cap). Less than 10 cents in quantity, and it can be used in other applications. Even has a shutdown input. --sp -- Best regards, Spehro Pefhany Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8 Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48
Reply by John Larkin December 8, 20152015-12-08
On 08 Dec 2015 11:22:12 GMT, Allan Herriman
<allanherriman@hotmail.com> wrote:

>On Mon, 07 Dec 2015 11:47:48 -0800, John Larkin wrote: > >> I need a wimpy diode, with lots of forward drop at a few mA, to bias up >> an e-phemt. Thought I'd try a small-geometry NPN transistor. >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/ >BCX70_as_Diode.JPG >> >> Looks good. The b-e and b-c junctions look symmetric. >> >> The middle config looks like the classic 60 mV/decade-current, and the >> others are maybe a little ohmic. We pay 2.4 cents each for these, so I >> don't mind wasting the transistor action. > > >I use a BAV199W if I want a high forward drop or vanishingly small >reverse current. Vf is not very well constrained by worst case limits in >the datasheet though. > >Allan
If you want crazy low reverse current, consider the c-b junction of a BFT25. https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/BFT25.JPG That reverse leakage was about at my measurement resolution limit. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by John Larkin December 8, 20152015-12-08
On Tue, 8 Dec 2015 09:45:03 +0000, piglet <erichpwagner@hotmail.com>
wrote:

>On 07/12/2015 19:47, John Larkin wrote: >> >> I need a wimpy diode, with lots of forward drop at a few mA, to bias >> up an e-phemt. Thought I'd try a small-geometry NPN transistor. >> > >How is that e-phemt Vgs bias point to change with temperature? Would the >B-E junction TC even be in the right direction? > >piglet >
I suspect that it's about the right amount and direction. I suppose I should measure it. Snarl. Snap. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by John Larkin December 8, 20152015-12-08
On Mon, 07 Dec 2015 21:31:47 -0800, Robert Baer
<robertbaer@localnet.com> wrote:

>John Larkin wrote: >> >> I need a wimpy diode, with lots of forward drop at a few mA, to bias >> up an e-phemt. Thought I'd try a small-geometry NPN transistor. >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/Transistors/BCX70_as_Diode.JPG >> >> Looks good. The b-e and b-c junctions look symmetric. >> >> The middle config looks like the classic 60 mV/decade-current, and the >> others are maybe a little ohmic. We pay 2.4 cents each for these, so I >> don't mind wasting the transistor action. >> >> >> >> >> > How come you seem to be the only one that shows READABLE (_not_ grey >on grey) drawings?
Sorry, I've never figured out how to do that. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com