John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:> >Has anybody done this? > >https://dl.dropbox.com/u/53724080/Circuits/Isrc_LED.JPGRed led? I've seen this many times in Elektor. -- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
LED reference current source
Started by ●September 9, 2012
Reply by ●September 10, 20122012-09-10
Reply by ●September 10, 20122012-09-10
On Mon, 10 Sep 2012 01:04:36 -0400, "krw@att.bizzzzzzzzzzzz" <krw@att.bizzzzzzzzzzzz> wrote:>On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Sun, 09 Sep 2012 23:59:32 -0400, "krw@att.bizzzzzzzzzzzz" >><krw@att.bizzzzzzzzzzzz> wrote: >> >>>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) >> >>That will have a tempco of around -0.4% per degree C. In theory an LED >>tc cancels the Vbe tc some. I just don't know how much. Google is >>ambiguous on the subject. >> >>I guess I'll have to build it and try it. We have some Osram LEDs that >>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they are >>a good candidate. > >If it's just an LED, who cares?It's a power-on indicator, too! -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●September 10, 20122012-09-10
On Mon, 10 Sep 2012 09:11:10 +0100, Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote:>On 10/09/2012 08:26, Tim Williams wrote: >> "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in >> message news:j5pq48d85781hruk3vj18j91s223blk0bl@4ax.com... >>>> Toob guys have been doing it for ages. Where 'ya been? >>> >>> Like, as in a VR tube and a p-channel triode? >> >> No, as shown... They do it in immitation of the SS amp guys, who have >> been doing it for even longer. >> >>> 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. >> >> I once had a chemistry lab about bandgap. We took a battery, LED and >> styrofoam cup of LN2, and proceeded to observe the color change upon >> putting them together. Theory from lecture said, cold --> crystal >> shrinks --> wavelength shrinks. > >That LN2 demo was always much more fun with the early generation of low=20 >efficiency red LEDs. The quantum efficiency rockets up when the lattice=20 >is cooled and thermal vibrations are decreased much more rigid lattice.=20 >Unfortunately they die after a few hundred cycles or less. > >I don't recall seeing the wavelength shift perceptably though the=20 >brightness changed by a very significant amount. Admitedly on a red led=20 >this could be both quantum efficiency and it producing shorter=20 >wavelength red light which is perceived as bright. ><snip>This may be due to human color perception sensitivities to wavelength shift in the red region, which is quite poor per unit wavelength shift. Discrimination between nearby wavelengths in the red region is not nearly as good as elsewhere. Did you use a spectrophotometer? Jon
Reply by ●September 10, 20122012-09-10
On Mon, 10 Sep 2012 12:34:54 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:>On Mon, 10 Sep 2012 01:04:36 -0400, "krw@att.bizzzzzzzzzzzz" ><krw@att.bizzzzzzzzzzzz> wrote: > >>On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin >><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Sun, 09 Sep 2012 23:59:32 -0400, "krw@att.bizzzzzzzzzzzz" >>><krw@att.bizzzzzzzzzzzz> wrote: >>> >>>>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) >>> >>>That will have a tempco of around -0.4% per degree C. In theory an LED >>>tc cancels the Vbe tc some. I just don't know how much. Google is >>>ambiguous on the subject. >>> >>>I guess I'll have to build it and try it. We have some Osram LEDs that >>>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they are >>>a good candidate. >> >>If it's just an LED, who cares? > >It's a power-on indicator, too!;-) I used the above circuit with green (SiC) LEDs directly off a LiIon battery to keep the intensity reasonably constant. A 20% variation over the 3.3-4.2V range was close enough (IIRC, it did a little better than that).
Reply by ●September 10, 20122012-09-10
On Mon, 10 Sep 2012 08:23:35 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Mon, 10 Sep 2012 01:22:29 -0700, miso <miso@sushi.com> wrote: > >>On 9/9/2012 10:21 PM, Grant wrote: >>> 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 >>> >>> I saw it decades ago for audio amp bias, claim was green LED >>> (old-style now, not high modern intensity types) balanced Vbe >>> tempco. >>> >>> Grant. >>> >>The high efficiency LEDs are double heterojuntion. When they first came >>out, the existing generation LED drives had insufficient compliance and >>produced a dimmer light than the standard LEDs. That is the high voltage >>of the double heterojunction LED made the drive chips put out less current. >> >>It wasn't like the LED companies gave the chip companies a heads up on >>the specs of the new generation LEDs so that the new driver chips would >>be available. > >Here are some numbers for the Osram LB T67C series, beautiful parts. > >https://dl.dropbox.com/u/53724080/Parts/OsramCurrents.JPGThe problem I had with Osram was that they melted in the RoHS process. KingBright had a much better package.
Reply by ●September 10, 20122012-09-10
On Sep 10, 9:34=A0pm, John Larkin <jlar...@highlandtechnology.com> wrote:> On Mon, 10 Sep 2012 01:04:36 -0400, "k...@att.bizzzzzzzzzzzz" > > > > > > > > > > <k...@att.bizzzzzzzzzzzz> wrote: > >On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > >>On Sun, 09 Sep 2012 23:59:32 -0400, "k...@att.bizzzzzzzzzzzz" > >><k...@att.bizzzzzzzzzzzz> wrote: > > >>>On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin > >>><jjlar...@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 juncti=on? I've> >>>used this (or the opposite sex) with6 really good results: > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Vcc > >>> =A0 =A0 =A0 =A0 =A0 =A0 +--------+ > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0V -> > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0- > >>> =A0 =A0 =A0 =A0 =A0 =A0.-. =A0 =A0 =A0 | > >>> =A0 =A0 =A0 =A0 =A0 =A0| | =A0 =A0 =A0 | > >>> =A0 =A0 =A0 =A0 =A0 =A0| | =A0 =A0||-+ > >>> =A0 =A0 =A0 =A0 =A0 =A0'-' =A0 =A0||<- > >>> =A0 =A0 =A0 =A0 =A0 =A0 +-----||-+ > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0\| =A0 =A0 =A0| > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 |------+ > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0<| =A0 =A0 =A0| > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 .-. > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | | > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | | > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 '-' > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| > >>> =A0 =A0 =A0 =A0 =A0 =A0 +--------+ > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Gnd > > >>>(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > >>That will have a tempco of around -0.4% per degree C. In theory an LED > >>tc cancels the Vbe tc some. I just don't know how much. Google is > >>ambiguous on the subject. > > >>I guess I'll have to build it and try it. We have some Osram LEDs that > >>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they are > >>a good candidate. > > >If it's just an LED, who cares? > > It's a power-on indicator, too!LEDS are - incidentally - photodiodes, so if you can see it, it can see enough of the external illumination to compromise its value as a voltage reference. This has already been pointed out elsewhere in this thread. -- Bill Sloman, Nijmegen
Reply by ●September 10, 20122012-09-10
On 10 Sep., 23:22, Bill Sloman <bill.slo...@ieee.org> wrote:> On Sep 10, 9:34=A0pm, John Larkin <jlar...@highlandtechnology.com> > wrote: > > > > > > > > > > > On Mon, 10 Sep 2012 01:04:36 -0400, "k...@att.bizzzzzzzzzzzz" > > > <k...@att.bizzzzzzzzzzzz> wrote: > > >On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin > > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > > >>On Sun, 09 Sep 2012 23:59:32 -0400, "k...@att.bizzzzzzzzzzzz" > > >><k...@att.bizzzzzzzzzzzz> wrote: > > > >>>On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin > > >>><jjlar...@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 junc=tion? I've> > >>>used this (or the opposite sex) with6 really good results: > > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Vcc > > >>> =A0 =A0 =A0 =A0 =A0 =A0 +--------+ > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0V -> > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0- > > >>> =A0 =A0 =A0 =A0 =A0 =A0.-. =A0 =A0 =A0 | > > >>> =A0 =A0 =A0 =A0 =A0 =A0| | =A0 =A0 =A0 | > > >>> =A0 =A0 =A0 =A0 =A0 =A0| | =A0 =A0||-+ > > >>> =A0 =A0 =A0 =A0 =A0 =A0'-' =A0 =A0||<- > > >>> =A0 =A0 =A0 =A0 =A0 =A0 +-----||-+ > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0\| =A0 =A0 =A0| > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 |------+ > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0<| =A0 =A0 =A0| > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 .-. > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | | > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | | > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 '-' > > >>> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| > > >>> =A0 =A0 =A0 =A0 =A0 =A0 +--------+ > > >>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Gnd > > > >>>(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) > > > >>That will have a tempco of around -0.4% per degree C. In theory an LE=D> > >>tc cancels the Vbe tc some. I just don't know how much. Google is > > >>ambiguous on the subject. > > > >>I guess I'll have to build it and try it. We have some Osram LEDs tha=t> > >>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they ar=e> > >>a good candidate. > > > >If it's just an LED, who cares? > > > It's a power-on indicator, too! > > LEDS are - incidentally - photodiodes, so if you can see it, it can > see enough of the external illumination to compromise its value as a > voltage reference. This has already been pointed out elsewhere in this > thread.I've seen learning remotes that used the IR led as a receiver when learning codes from other remotes, but I wonder how much external light will affect a LED that is already on. might wanna check if that current source gets a 50/60Hz ac on it when exposed to light -Lasse
Reply by ●September 10, 20122012-09-10
On Mon, 10 Sep 2012 14:22:03 -0700 (PDT), Bill Sloman <bill.sloman@ieee.org> wrote:>On Sep 10, 9:34�pm, John Larkin <jlar...@highlandtechnology.com> >wrote: >> On Mon, 10 Sep 2012 01:04:36 -0400, "k...@att.bizzzzzzzzzzzz" >> >> >> >> >> >> >> >> >> >> <k...@att.bizzzzzzzzzzzz> wrote: >> >On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> >>On Sun, 09 Sep 2012 23:59:32 -0400, "k...@att.bizzzzzzzzzzzz" >> >><k...@att.bizzzzzzzzzzzz> wrote: >> >> >>>On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin >> >>><jjlar...@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 04/19/05www.tech-chat.de) >> >> >>That will have a tempco of around -0.4% per degree C. In theory an LED >> >>tc cancels the Vbe tc some. I just don't know how much. Google is >> >>ambiguous on the subject. >> >> >>I guess I'll have to build it and try it. We have some Osram LEDs that >> >>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they are >> >>a good candidate. >> >> >If it's just an LED, who cares? >> >> It's a power-on indicator, too! > >LEDS are - incidentally - photodiodes, so if you can see it, it can >see enough of the external illumination to compromise its value as a >voltage reference. This has already been pointed out elsewhere in this >thread.Yes, it has. What is your contribution? Numbers matter. Nanoamps over milliamps equals parts per million. It's easy enough to try. I'm soldering up a breadboard now. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●September 10, 20122012-09-10
Bill Sloman wrote:> > On Sep 10, 9:34 pm, John Larkin <jlar...@highlandtechnology.com> > wrote: > > On Mon, 10 Sep 2012 01:04:36 -0400, "k...@att.bizzzzzzzzzzzz" > > > > > > > > > > > > > > > > > > > > <k...@att.bizzzzzzzzzzzz> wrote: > > >On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin > > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > > > >>On Sun, 09 Sep 2012 23:59:32 -0400, "k...@att.bizzzzzzzzzzzz" > > >><k...@att.bizzzzzzzzzzzz> wrote: > > > > >>>On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin > > >>><jjlar...@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 04/19/05www.tech-chat.de) > > > > >>That will have a tempco of around -0.4% per degree C. In theory an LED > > >>tc cancels the Vbe tc some. I just don't know how much. Google is > > >>ambiguous on the subject. > > > > >>I guess I'll have to build it and try it. We have some Osram LEDs that > > >>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they are > > >>a good candidate. > > > > >If it's just an LED, who cares? > > > > It's a power-on indicator, too! > > LEDS are - incidentally - photodiodes, so if you can see it, it can > see enough of the external illumination to compromise its value as a > voltage reference. This has already been pointed out elsewhere in this > thread.LEDs are really crappy photodiodes, though, because they're direct-bandgap devices with only a few nanoseconds' minority carrier lifetime. High-level injection conditions (e.g. a small diode with a few milliamps of forward bias) make them a lot crappier. It would be very difficult to get more than a few hundred nanoamps out of a LED used as a photodiode in indoor ambient conditions, even with the box taken apart. So assuming it has a few milliamps' forward bias, that's maybe 1 part in 10**4 if you're unlucky, i.e. about 2.6 uV out of a volt or so. Since nobody is proposing to use LEDs for references for>12 bit DACs, I wouldn't worry too much.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 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●September 10, 20122012-09-10
<langwadt@fonz.dk> wrote in message news:0c06e4a7-1ac4-4a69-bbb9-c7bc687ade5f@ib4g2000vbb.googlegroups.com... On 10 Sep., 23:22, Bill Sloman <bill.slo...@ieee.org> wrote:> On Sep 10, 9:34 pm, John Larkin <jlar...@highlandtechnology.com> > wrote: > > > > > > > > > > > On Mon, 10 Sep 2012 01:04:36 -0400, "k...@att.bizzzzzzzzzzzz" > > > <k...@att.bizzzzzzzzzzzz> wrote: > > >On Sun, 09 Sep 2012 21:28:55 -0700, John Larkin > > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > > > >>On Sun, 09 Sep 2012 23:59:32 -0400, "k...@att.bizzzzzzzzzzzz" > > >><k...@att.bizzzzzzzzzzzz> wrote: > > > >>>On Sun, 09 Sep 2012 18:50:25 -0700, John Larkin > > >>><jjlar...@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 04/19/05www.tech-chat.de) > > > >>That will have a tempco of around -0.4% per degree C. In theory an LED > > >>tc cancels the Vbe tc some. I just don't know how much. Google is > > >>ambiguous on the subject. > > > >>I guess I'll have to build it and try it. We have some Osram LEDs that > > >>are a gorgeous orange color, about 1.8 volts drop at 1 mA, so they are > > >>a good candidate. > > > >If it's just an LED, who cares? > > > It's a power-on indicator, too! > > LEDS are - incidentally - photodiodes, so if you can see it, it can > see enough of the external illumination to compromise its value as a > voltage reference. This has already been pointed out elsewhere in this > thread.I've seen learning remotes that used the IR led as a receiver when learning codes from other remotes, but I wonder how much external light will affect a LED that is already on. might wanna check if that current source gets a 50/60Hz ac on it when exposed to light ++++++++++++++++++++++++++++++++++++++++++++ Also check under CFL light. They put out a lot of trash.
