Fast, efficient IR LEDs?
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From: miso on 6 Feb 2010 16:09 On Feb 6, 12:51 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > On 2/6/2010 3:13 PM, Joerg wrote: > > > > > Phil Hobbs wrote: > >> On 2/6/2010 12:41 PM, Joerg wrote: > >>> m...(a)sushi.com wrote: > >>>> On Feb 5, 2:20 pm, Joerg <inva...(a)invalid.invalid> wrote: > >>>>> Phil Hobbs wrote: > >>>>>> On 2/5/2010 2:13 PM, m...(a)sushi.com wrote: > >>>>>>> On Feb 5, 8:56 am, Phil > >>>>>>> Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> > >>>>>>> wrote: > >>>>>>>> I need a fast IR LED (> 20 MHz,< 50 pF) for an optical feedback > >>>>>>>> gizmo. > >>>>>>>> I have some Stanley DN310s, but they've been discontinued. Other > >>>>>>>> possibilities are: > >>>>>>>> Vishay TSFF5410 -- 870 nm, 0.% W/A typ 15 ns rise/fall, 125 pF typ > >>>>>>>> Vishay VSLB3940 -- 940 nm, 0.4 W/A typ 15 ns rise/fall, 70 pF typ > >>>>>>>> Panasonic LNA4905L -- 880 nm, 0.3 W/A min 30 MHz typ, no other > >>>>>>>> specs > >>>>>>>> Osram SFH4550 -- 850 nm, 0.5 W/A typ 12 ns rise/fall, no C spec > >>>>>>>> It would be really nice to find something with a flat front > >>>>>>>> facet and > >>>>>>>> (especially) lower capacitance, because it has to work at quite low > >>>>>>>> currents (5-10 uA). > >>>>>>>> Any suggestions? > >>>>>>>> Thanks > >>>>>>>> Phil Hobbs > >>>>>>> Isn't low current and high speed mutually exclusive, like > >>>>>>> intelligence > >>>>>>> and Republicans? > >>>>>> Nice try, Soup. ;) I enjoy talking electronics too much though. > >>>>> His "email address" always makes me crave miso soup and sushi. So, we > >>>>> just went to the Japanese restaurant in town ... > > >>>>> But this time I had pork teriyaki after the miso soup. We usually have > >>>>> sushi in the evenings, I can't really work after that, it's so good > >>>>> that > >>>>> I tend to eat too much of it. > > >>>>> -- > >>>>> Regards, Joerg > > >>>>>http://www.analogconsultants.com/ > > >>>>> "gmail" domain blocked because of excessive spam. > >>>>> Use another domain or send PM. > > >>>> Sushi doesn't make for an evening meal. Just too light, even when > >>>> supplemented with miso soup. It's better for lunch. > > >>> 4-5 rolls (servings) with 4 people and I am really stuffed afterwards.. > >>> But it's delicious. > > >>>> Getting back to electronics., this is really an i=c*dv/dt issue. It > >>>> seems to me all you can do is reduce C if current is limited. > > >>> If Phil has to switch constantly, yes. Otherwise there could be a > >>> "spiking circuit" that swings the C with gusto. > > >> It's inside a feedback loop that needs to have >1 MHz bandwidth, so > >> it's more a loop stability vs bandwidth issue. There are alternatives, > >> but they're all more complicated than what we've got. I'd probably > >> prefer to trade off efficiency rather than speed and capacitance. > > > Then you'll probably be in the market for the good stuff. This is an > > example of one I've used in an optical feedback situation. I only needed > > a little under 100MHz BW but it could have given me a lot more: > > >http://www.excelight.com/pdf/device/PD/SPT2400-x(revC).pdf > > Hopefully not--that's megahertz, not gigahertz. But I do want to be > able to work down at 500 nA or 1 uA. > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058 > hobbs at electrooptical dot nethttp://electrooptical.net By "spike", Joerg is referring to dynamic biasing. A common technique is micropower designs. You juice up the current under conditions that need the bandwidth, then relax to the low bandwidth state. This can lead to instability, so you need to be careful. [Poles will be dynamic too.] Thinking aloud here, I would guess the only way you can get this circuit to be high speed and low power is to use optical feedback on the led itself. If you have a photodiode that monitors the led and you see it lagging, the feedback can provide the overdrive. I guess voltage feedback at the led could do that to, but that would be tricky since the led is a nonlinear load. The optical feedback scheme isn't really low power, but it can lead to the lowest power solution. That is, you can't fight physics, but you can design with efficiency, only using high current when you need it.
From: Tim Williams on 6 Feb 2010 20:11 "Phil Hobbs" <pcdhSpamMeSenseless(a)electrooptical.net> wrote in message news:4B6C629D.7010008(a)electrooptical.net... > The IRDA application is why they need speed specs, and nobody does IRDA in > the visible. Obviously. So start your own VDA! ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 6 Feb 2010 20:14 "Robert Baer" <robertbaer(a)localnet.com> wrote in message news:Ys2dnQjtwt7DmfDWnZ2dnUVZ_u5i4p2d(a)posted.localnet... > How about a 40V shunt regulator that varies less than 2V from 25C down > to -70C (or less)? > Is that COOL or what? TL431, 12V zener to soak up the 10V past Vka(max), and two resistors. TL431 isn't usually spec'd as low as -70C though. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: JosephKK on 7 Feb 2010 12:06 On Fri, 05 Feb 2010 11:43:30 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 5 Feb 2010 11:13:02 -0800 (PST), "miso(a)sushi.com" ><miso(a)sushi.com> wrote: > >>On Feb 5, 8:56 am, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> >>wrote: >>> I need a fast IR LED (> 20 MHz, < 50 pF) for an optical feedback gizmo. >>> I have some Stanley DN310s, but they've been discontinued. Other >>> possibilities are: >>> >>> Vishay TSFF5410 -- 870 nm, 0.% W/A typ 15 ns rise/fall, 125 pF typ >>> Vishay VSLB3940 -- 940 nm, 0.4 W/A typ 15 ns rise/fall, 70 pF typ >>> Panasonic LNA4905L -- 880 nm, 0.3 W/A min 30 MHz typ, no other specs >>> Osram SFH4550 -- 850 nm, 0.5 W/A typ 12 ns rise/fall, no C spec >>> >>> It would be really nice to find something with a flat front facet and >>> (especially) lower capacitance, because it has to work at quite low >>> currents (5-10 uA). >>> >>> Any suggestions? >>> >>> Thanks >>> >>> Phil Hobbs >>> >>> PS: Amazing how we're actually talking about electronics at the moment! >>> >>> -- >>> Dr Philip C D Hobbs >>> Principal >>> ElectroOptical Innovations >>> 55 Orchard Rd >>> Briarcliff Manor NY 10510 >>> 845-480-2058 >>> hobbs at electrooptical dot nethttp://electrooptical.net >> >>Isn't low current and high speed mutually exclusive, like intelligence >>and Republicans? > >Ah, politics! > >I wonder why lefties always assume that conservatives are stupid. >That's the "what's wrong with Kansas?" dilemma, the lament that the >working class won't toe the party line and follow the lead of their >betters. > >Conservatives generally assume that lefties are both stupid and evil. > >John _ALL_ politicians are evil, ignorant, and arrogant; these are the basic requirements just to run for office.
From: JosephKK on 7 Feb 2010 12:29
On Sat, 06 Feb 2010 15:51:29 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >On 2/6/2010 3:13 PM, Joerg wrote: >> Phil Hobbs wrote: >>> On 2/6/2010 12:41 PM, Joerg wrote: >>>> miso(a)sushi.com wrote: >>>>> On Feb 5, 2:20 pm, Joerg <inva...(a)invalid.invalid> wrote: >>>>>> Phil Hobbs wrote: >>>>>>> On 2/5/2010 2:13 PM, m...(a)sushi.com wrote: >>>>>>>> On Feb 5, 8:56 am, Phil >>>>>>>> Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> >>>>>>>> wrote: >>>>>>>>> I need a fast IR LED (> 20 MHz,< 50 pF) for an optical feedback >>>>>>>>> gizmo. >>>>>>>>> I have some Stanley DN310s, but they've been discontinued. Other >>>>>>>>> possibilities are: >>>>>>>>> Vishay TSFF5410 -- 870 nm, 0.% W/A typ 15 ns rise/fall, 125 pF typ >>>>>>>>> Vishay VSLB3940 -- 940 nm, 0.4 W/A typ 15 ns rise/fall, 70 pF typ >>>>>>>>> Panasonic LNA4905L -- 880 nm, 0.3 W/A min 30 MHz typ, no other >>>>>>>>> specs >>>>>>>>> Osram SFH4550 -- 850 nm, 0.5 W/A typ 12 ns rise/fall, no C spec >>>>>>>>> It would be really nice to find something with a flat front >>>>>>>>> facet and >>>>>>>>> (especially) lower capacitance, because it has to work at quite low >>>>>>>>> currents (5-10 uA). >>>>>>>>> Any suggestions? >>>>>>>>> Thanks >>>>>>>>> Phil Hobbs >>>>>>>> Isn't low current and high speed mutually exclusive, like >>>>>>>> intelligence >>>>>>>> and Republicans? >>>>>>> Nice try, Soup. ;) I enjoy talking electronics too much though. >>>>>> His "email address" always makes me crave miso soup and sushi. So, we >>>>>> just went to the Japanese restaurant in town ... >>>>>> >>>>>> But this time I had pork teriyaki after the miso soup. We usually have >>>>>> sushi in the evenings, I can't really work after that, it's so good >>>>>> that >>>>>> I tend to eat too much of it. >>>>>> >>>>>> -- >>>>>> Regards, Joerg >>>>>> >>>>>> http://www.analogconsultants.com/ >>>>>> >>>>>> "gmail" domain blocked because of excessive spam. >>>>>> Use another domain or send PM. >>>>> >>>>> Sushi doesn't make for an evening meal. Just too light, even when >>>>> supplemented with miso soup. It's better for lunch. >>>>> >>>> >>>> 4-5 rolls (servings) with 4 people and I am really stuffed afterwards. >>>> But it's delicious. >>>> >>>> >>>>> Getting back to electronics., this is really an i=c*dv/dt issue. It >>>>> seems to me all you can do is reduce C if current is limited. >>>> >>>> >>>> If Phil has to switch constantly, yes. Otherwise there could be a >>>> "spiking circuit" that swings the C with gusto. >>>> >>> >>> It's inside a feedback loop that needs to have >1 MHz bandwidth, so >>> it's more a loop stability vs bandwidth issue. There are alternatives, >>> but they're all more complicated than what we've got. I'd probably >>> prefer to trade off efficiency rather than speed and capacitance. >>> >> >> Then you'll probably be in the market for the good stuff. This is an >> example of one I've used in an optical feedback situation. I only needed >> a little under 100MHz BW but it could have given me a lot more: >> >> http://www.excelight.com/pdf/device/PD/SPT2400-x(revC).pdf >> > >Hopefully not--that's megahertz, not gigahertz. But I do want to be >able to work down at 500 nA or 1 uA. > >Cheers > >Phil Hobbs You may wish to consider a laser diode operating below critical current. |