Blue LED at 3.3V
in [Design]
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From: John Larkin on 26 May 2010 18:10 On Wed, 26 May 2010 07:31:33 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On May 26, 8:00�am, David Eather <eat...(a)tpg.com.au> wrote: >> On 26/05/2010 4:10 AM, John Larkin wrote: >> >> >> >> >> >> > On Tue, 25 May 2010 10:22:59 -0700, Tim Wescott<t...(a)seemywebsite.now> >> > wrote: >> >> >> On 05/25/2010 10:18 AM, rich wrote: >> >>> I need to drive a blue led from 3.3V. �Most of the SMD blue leds I >> >>> find have a Vf equal to or greater than 3.3V. >> >> >>> I am curious how others are dealing with this. >> >> >> That pretty much demands a voltage boost of some sort. �Depending on how >> >> many lights you have, how much power you're willing to waste, how much >> >> design time you want to spend and how expensive you want the final >> >> product to be, your choices sort of boil down to a switcher with >> >> inductors and diodes and all that, or a current pump. >> >> >> Most of us would solve this problem by looking for a suitable IC. >> >> _Some_ of us would do it with two transistors, an inductor, and a cap, >> >> then brag about only needing one $.001 resistor instead of three. >> >> > One resistor: >> >> >ftp://jjlarkin.lmi.net/LED_boost.JPG >> >> > John >> >> Hi, >> >> Could you post his circuit onwww.filedropper.comorwww.filefactory.com >> or something similar - I just can connect.- Hide quoted text - >> >> - Show quoted text - > > > >+3.3V----+-----------+ > | | > |\| V This is diode or R > | \ - > +--+| >--+-CC---+ > | | / | | > | |/| | V light comes out here > +------RR--+ - > | > GND > >The IC is a schmitt trigger. (And connected to ground also... >connection not shown) > >George H. > > The schmitt has to be an inverter to oscillate, of course. I left out the bubble. RR could be a short, then it would oscillate faster! John
From: Jim Thompson on 26 May 2010 18:29 On Wed, 26 May 2010 15:10:15 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 26 May 2010 07:31:33 -0700 (PDT), George Herold ><gherold(a)teachspin.com> wrote: > >>On May 26, 8:00�am, David Eather <eat...(a)tpg.com.au> wrote: >>> On 26/05/2010 4:10 AM, John Larkin wrote: >>> >>> >>> >>> >>> >>> > On Tue, 25 May 2010 10:22:59 -0700, Tim Wescott<t...(a)seemywebsite.now> >>> > wrote: >>> >>> >> On 05/25/2010 10:18 AM, rich wrote: >>> >>> I need to drive a blue led from 3.3V. �Most of the SMD blue leds I >>> >>> find have a Vf equal to or greater than 3.3V. >>> >>> >>> I am curious how others are dealing with this. >>> >>> >> That pretty much demands a voltage boost of some sort. �Depending on how >>> >> many lights you have, how much power you're willing to waste, how much >>> >> design time you want to spend and how expensive you want the final >>> >> product to be, your choices sort of boil down to a switcher with >>> >> inductors and diodes and all that, or a current pump. >>> >>> >> Most of us would solve this problem by looking for a suitable IC. >>> >> _Some_ of us would do it with two transistors, an inductor, and a cap, >>> >> then brag about only needing one $.001 resistor instead of three. >>> >>> > One resistor: >>> >>> >ftp://jjlarkin.lmi.net/LED_boost.JPG >>> >>> > John >>> >>> Hi, >>> >>> Could you post his circuit onwww.filedropper.comorwww.filefactory.com >>> or something similar - I just can connect.- Hide quoted text - >>> >>> - Show quoted text - >> >> >> >>+3.3V----+-----------+ >> | | >> |\| V This is diode or R >> | \ - >> +--+| >--+-CC---+ >> | | / | | >> | |/| | V light comes out here >> +------RR--+ - >> | >> GND >> >>The IC is a schmitt trigger. (And connected to ground also... >>connection not shown) >> >>George H. >> >> > >The schmitt has to be an inverter to oscillate, of course. I left out >the bubble. > >RR could be a short, then it would oscillate faster! > >John Excuses! Excuses! Excuses! Where does a capacitor belong? (Giving you the benefit of even having a clue :-) ...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 | The only thing bipartisan in this country is hypocrisy
From: Grant on 26 May 2010 18:51 On Wed, 26 May 2010 15:29:21 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Wed, 26 May 2010 15:10:15 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Wed, 26 May 2010 07:31:33 -0700 (PDT), George Herold >><gherold(a)teachspin.com> wrote: >> >>>On May 26, 8:00 am, David Eather <eat...(a)tpg.com.au> wrote: >>>> On 26/05/2010 4:10 AM, John Larkin wrote: >>>> >>>> >>>> >>>> >>>> >>>> > On Tue, 25 May 2010 10:22:59 -0700, Tim Wescott<t...(a)seemywebsite.now> >>>> > wrote: >>>> >>>> >> On 05/25/2010 10:18 AM, rich wrote: >>>> >>> I need to drive a blue led from 3.3V. Most of the SMD blue leds I >>>> >>> find have a Vf equal to or greater than 3.3V. >>>> >>>> >>> I am curious how others are dealing with this. >>>> >>>> >> That pretty much demands a voltage boost of some sort. Depending on how >>>> >> many lights you have, how much power you're willing to waste, how much >>>> >> design time you want to spend and how expensive you want the final >>>> >> product to be, your choices sort of boil down to a switcher with >>>> >> inductors and diodes and all that, or a current pump. >>>> >>>> >> Most of us would solve this problem by looking for a suitable IC. >>>> >> _Some_ of us would do it with two transistors, an inductor, and a cap, >>>> >> then brag about only needing one $.001 resistor instead of three. >>>> >>>> > One resistor: >>>> >>>> >ftp://jjlarkin.lmi.net/LED_boost.JPG >>>> >>>> > John >>>> >>>> Hi, >>>> >>>> Could you post his circuit onwww.filedropper.comorwww.filefactory.com >>>> or something similar - I just can connect.- Hide quoted text - >>>> >>>> - Show quoted text - >>> >>> >>> >>>+3.3V----+-----------+ >>> | | >>> |\| V This is diode or R >>> | \ - >>> +--+| >--+-CC---+ >>> | | / | | >>> | |/| | V light comes out here >>> +------RR--+ - >>> | >>> GND >>> >>>The IC is a schmitt trigger. (And connected to ground also... >>>connection not shown) >>> >>>George H. >>> >>> >> >>The schmitt has to be an inverter to oscillate, of course. I left out >>the bubble. >> >>RR could be a short, then it would oscillate faster! >> >>John > >Excuses! Excuses! Excuses! Where does a capacitor belong? Stray? > (Giving >you the benefit of even having a clue :-) Grant. -- http://bugs.id.au/
From: John Larkin on 26 May 2010 18:59 On Thu, 27 May 2010 08:51:22 +1000, Grant <omg(a)grrr.id.au> wrote: >On Wed, 26 May 2010 15:29:21 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > >>On Wed, 26 May 2010 15:10:15 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Wed, 26 May 2010 07:31:33 -0700 (PDT), George Herold >>><gherold(a)teachspin.com> wrote: >>> >>>>On May 26, 8:00�am, David Eather <eat...(a)tpg.com.au> wrote: >>>>> On 26/05/2010 4:10 AM, John Larkin wrote: >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> > On Tue, 25 May 2010 10:22:59 -0700, Tim Wescott<t...(a)seemywebsite.now> >>>>> > wrote: >>>>> >>>>> >> On 05/25/2010 10:18 AM, rich wrote: >>>>> >>> I need to drive a blue led from 3.3V. �Most of the SMD blue leds I >>>>> >>> find have a Vf equal to or greater than 3.3V. >>>>> >>>>> >>> I am curious how others are dealing with this. >>>>> >>>>> >> That pretty much demands a voltage boost of some sort. �Depending on how >>>>> >> many lights you have, how much power you're willing to waste, how much >>>>> >> design time you want to spend and how expensive you want the final >>>>> >> product to be, your choices sort of boil down to a switcher with >>>>> >> inductors and diodes and all that, or a current pump. >>>>> >>>>> >> Most of us would solve this problem by looking for a suitable IC. >>>>> >> _Some_ of us would do it with two transistors, an inductor, and a cap, >>>>> >> then brag about only needing one $.001 resistor instead of three. >>>>> >>>>> > One resistor: >>>>> >>>>> >ftp://jjlarkin.lmi.net/LED_boost.JPG >>>>> >>>>> > John >>>>> >>>>> Hi, >>>>> >>>>> Could you post his circuit onwww.filedropper.comorwww.filefactory.com >>>>> or something similar - I just can connect.- Hide quoted text - >>>>> >>>>> - Show quoted text - >>>> >>>> >>>> >>>>+3.3V----+-----------+ >>>> | | >>>> |\| V This is diode or R >>>> | \ - >>>> +--+| >--+-CC---+ >>>> | | / | | >>>> | |/| | V light comes out here >>>> +------RR--+ - >>>> | >>>> GND >>>> >>>>The IC is a schmitt trigger. (And connected to ground also... >>>>connection not shown) >>>> >>>>George H. >>>> >>>> >>> >>>The schmitt has to be an inverter to oscillate, of course. I left out >>>the bubble. >>> >>>RR could be a short, then it would oscillate faster! >>> >>>John >> >>Excuses! Excuses! Excuses! Where does a capacitor belong? > >Stray? Sure. CMOS ICs have input capacitance. I guess JT doesn't know much about CMOS ICs. I obviously left out the cap, on purpose, to hit the "one resistor" target. It *will* oscillate without a discrete cap. What else could it possibly do? John
From: Don Klipstein on 26 May 2010 19:08
In article <903qv55fpsfvvorh9u76arcl368lm29ik6(a)4ax.com>, Rich Webb wrote: >On Wed, 26 May 2010 12:26:16 +0200, Uwe Hercksen ><hercksen(a)mew.uni-erlangen.de> wrote: >> >>Tim Wescott schrieb: >> >>> AFAIK a white LED is just a blue LED chip with some fluorescent material >>> in the package that makes enough "whatever else" to make it look white. >>> >>> They look exceedingly blue to me -- I don't know if that's because they >>> are, or because I'm color deficient in green and don't see them the same >>> as other people do. >> >>they mix the blue light with yellow light from the fluorescent material, >>but it is a very narrow blue band and a very broad yellow band. If you >>look at a spectrum diagram of the resulting light it looks very >>different to white light from the sun or from a ligth bulb with a >>glowing tungsten wire. > >Some may indeed by bi-chromic but the ones that I've examined recently >with a handheld spectroscope have a remarkably even spectrum from about >420 to 680 nm. It's not a quantitative instrument but there were no >obvious emission or absorption lines. Surprised me, in a good way. I find the spectrum to be smooth, but not even. I see the spectrum running low in truly and fairly violet wavelengths. (Shorter than 430 nm, though that actually means little as far as practical illumination is concerned since in that part of the spectrum, human vision has low sensitivity.) Another irregularity that I see is the "blue peak" - usually visible to me as a "brightish hump" in the spectrum, even if I merely use a CD as a diffraction grating to view the spectrum. The reduction in diversity of blue/bluish wavelengths has some negative impact on color rendering properties, probably minor. The next irregularity that I see is a dip/weakness in the blue-green to bluish side of mid-green. I find that to have a minor negative effect on color rendering. Another thing I find that to have is to make the light's "scotopic/photopic ratio" or "s/p ratio" less than that of daylight or blackbody radiation of the same color. That affects illumination ability in dimmer environments where scotopic vision or mesopic vision (both scotopic and photopic are significantly functioning) is the vision mode that is being used. After that, comes the irregularity of surplus of yellow and yellow-orange and shortage of mid-green (even if shortage is only on bluish side of mid-green) and shortage of mid-red. (The "red shortage" is even worse in the deep red, but that matters less due to low sensitivity of human vision to deep red.) This irregularity causes dulling of the color of green things, and dulling and darkening of the color of red things. As the years have gone by, it appears to me that the color rendering index of white LEDs (excluding enhanced or high CRI models) has drifted downwards, from 75-plus of older ones around and before 2000 to around 65 for the highest efficency recent ones as of 2009. One reason is that advancement of the phosphors used for these included narrowing the yellowish emission band of the phosphor to produce less bluish-green and blue-side-mid-green and less deep red and deeper mid-red, and more yellow and greenish-yellow. Another is that the "blue peak" wavelength has been shifted shorter in highest-efficiency white LEDs, from around 467 nm in the late 1990's to closer to 450 nm now. Shifting the "blue peak" towards 450 or upper 440's of nm makes that spectral feature hit the "blue peak" of human vision better, and that means less blue light has to escape the LED in question to make white light, and more of the blue light can be converted to yellowish light that human vision is more sensitive to in photometric terms. However, this shift does deepen the "blue-green valley" and also decreases s/p ratio. For examples of white LEDs: Older style spectrum: Nichia NSPW500S, NSPW500CS. Especially NSPW500S, some of which may still be available from some nationally-selling-to- hobbyists electronic surplus outfits. That LED is often noted as a 5600 MCD white LED. These have nominal color temperature of 6500 K, but appear to me more like 6000 K. I determined a Nichia NSPWF50DS to have s/p ratio of 2.3, which is only slightly short of the 2.36 of a 6000K blackbody or the 2.45 of 6500K. An extreme newer style spectrum: Nichia NSPWR70CSS-K1, which Nichia claims to achieve 150 lumens out per watt in at 20 mA. I have personally tested these to achieve 140-145 lumens/watt at 20 mA by a method prone to erring on the conservative side. The nominal color temperature is 5000 K. I have determined s/p ratio to be 1.7, while a 5000K blackbody achieves 2.15. I have also determined *some* red object color/brightness rendering properties and a few other color rendering properties that I can determine numerically to be like those of a common fluorescent lamp whose CRI is 62, so I "guesstimate" that this LED's CRI (specifically the Ra8 CRI) is 62-65. I can name two other nominally 5000K LEDs stated by their manufacturer to have CRI of 65, at least IIRC: Citizen / Cecol CL-L233-C13N and CL-654-C1N. One was on and the other was hardly behind the bleeding cutting edge of overall luminous efficacy for LEDs of their power class when they became available, with convenient higher voltage drops (muti-chip), considering competition that was actually available then, even at ~3.2-3.5V voltage drop. The lower efficiency of those two even has its 8 chips isolated from each other (16 contact package) and IIRC rated to be paralleled with each other, allowing choice of 3 options for voltage drop. -- - Don Klipstein (don(a)misty.com) |