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LED reference current source

Started by John Larkin September 9, 2012
Has anybody done this?

https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG



-- 

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>Has anybody done this? > >https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG
Must have been, since I just saw some discussion about it on LTspice group less than a month ago. Jon
On Sun, 9 Sep 2012 22:04:13 -0400, "tm"
<No_one_home@white-house.gov> wrote:

> >"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in =
message=20
>news:iphq48dvaejq1p99fnjp2jj159pod18823@4ax.com... >> >> Has anybody done this? >> >> https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG >> >> --=20 > >Do you need or want the base resistor?=20
He spec'd an RF transistor and JL sticks base resistors on BJT bases like others put bypass caps on ICs. Everywhere. Jon
On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

> >Has anybody done this? > >https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG
What is it supposed to buy you? Does the LED forward TC match a Silicon Vbe TC? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message 
news:iphq48dvaejq1p99fnjp2jj159pod18823@4ax.com...
> > Has anybody done this? > > https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG > > > > --
Do you need or want the base resistor?
On Sun, 09 Sep 2012 19:03:26 -0700, Jon Kirwan
<jonk@infinitefactors.org> wrote:

>On Sun, 9 Sep 2012 22:04:13 -0400, "tm" ><No_one_home@white-house.gov> wrote: > >> >>"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message >>news:iphq48dvaejq1p99fnjp2jj159pod18823@4ax.com... >>> >>> Has anybody done this? >>> >>> https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG >>> >>> -- >> >>Do you need or want the base resistor? > >He spec'd an RF transistor and JL sticks base resistors on >BJT bases like others put bypass caps on ICs. Everywhere. > >Jon
Only if there's a resistor in the emitter. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Sun, 09 Sep 2012 19:05:51 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>On Sun, 09 Sep 2012 19:03:26 -0700, Jon Kirwan ><jonk@infinitefactors.org> wrote: > >>On Sun, 9 Sep 2012 22:04:13 -0400, "tm" >><No_one_home@white-house.gov> wrote: >> >>> >>>"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in =
message=20
>>>news:iphq48dvaejq1p99fnjp2jj159pod18823@4ax.com... >>>> >>>> Has anybody done this? >>>> >>>> https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG >>>> >>>> --=20 >>> >>>Do you need or want the base resistor?=20 >> >>He spec'd an RF transistor and JL sticks base resistors on >>BJT bases like others put bypass caps on ICs. Everywhere. >> >>Jon > >Only if there's a resistor in the emitter.
Yup. ;) Jon
Toob guys have been doing it for ages.  Where 'ya been?

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in 
message news:iphq48dvaejq1p99fnjp2jj159pod18823@4ax.com...
> > Has anybody done this? > > https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG > > > > -- > > John Larkin Highland Technology Inc > www.highlandtechnology.com jlarkin at highlandtechnology dot com > > Precision electronic instrumentation > Picosecond-resolution Digital Delay and Pulse generators > Custom timing and laser controllers > Photonics and fiberoptic TTL data links > VME analog, thermocouple, LVDT, synchro, tachometer > Multichannel arbitrary waveform generators
On Sun, 9 Sep 2012 22:39:03 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:

>Toob guys have been doing it for ages. Where 'ya been?
Like, as in a VR tube and a p-channel triode? As far as doing it with semiconductors, there seems to be a lot of different chemistries in LEDs, namely lots of different forward voltage curves for a diveb color, and not much data about tempcos. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

> >Has anybody done this? > >https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPG
Is there any significant matching between the LED and the Si BE junction? I've used this (or the opposite sex) with6 really good results: Vcc +--------+ | | | V -> | - .-. | | | | | | ||-+ '-' ||<- +-----||-+ | | \| | |------+ <| | | .-. | | | | | | | '-' | | +--------+ Gnd (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)