Blue LED at 3.3V
in [Design]
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From: Jan Panteltje on 26 May 2010 11:57 On a sunny day (Wed, 26 May 2010 08:07:44 -0400) it happened Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote in <pl3qv51sgc9qpu3gikgkttjov9n3e5e1v7(a)4ax.com>: >On Wed, 26 May 2010 10:10:52 GMT, the renowned Jan Panteltje ><pNaonStpealmtje(a)yahoo.com> wrote: > > >>I wanted to say: >>Just use resistor to heat up the LED. >>Perhaps a NTC could be used, not sure if it would be easy to fidn teh right one, >>and mount it next to the lED in parallel with the supply... >> >>Now somebody could invent a LED with all that build in, photo sensor too, >>to keep light output at a progammable (I2C perhaps) level. >>Little switcher inside? Current limiter... This is the age of integration, >>logic level I2C input. > >Maybe a TEC and controller to control the wavelength? > >Do you really want LEDs with 80 page manuals (and 5 pages of errata)? >;-) Oh well, one gets used to things :-)
From: John Larkin on 26 May 2010 12:09 On Wed, 26 May 2010 08:07:44 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Wed, 26 May 2010 10:10:52 GMT, the renowned Jan Panteltje ><pNaonStpealmtje(a)yahoo.com> wrote: > > >>I wanted to say: >>Just use resistor to heat up the LED. >>Perhaps a NTC could be used, not sure if it would be easy to fidn teh right one, >>and mount it next to the lED in parallel with the supply... >> >>Now somebody could invent a LED with all that build in, photo sensor too, >>to keep light output at a progammable (I2C perhaps) level. >>Little switcher inside? Current limiter... This is the age of integration, >>logic level I2C input. > >Maybe a TEC and controller to control the wavelength? > >Do you really want LEDs with 80 page manuals (and 5 pages of errata)? >;-) > > >Best regards, >Spehro Pefhany We don't yet use any parts with thousand-page datasheets, but we do have a couple over 800. And the longer the manual, the worse it seems to be. John
From: John Fields on 26 May 2010 12:19 On Wed, 26 May 2010 07:24:46 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: .. .. .. >Hmmm, neither C may matter. It might all cancel out. Somebody should >do the math. Who better than the designer? Besides, that circuit won't work as drawn.
From: Jim Thompson on 26 May 2010 12:23 On Wed, 26 May 2010 05:04:00 +0000 (UTC), don(a)manx.misty.com (Don Klipstein) wrote: >In article <ti4ov551ahdt2po32gjcie9km7gg4a1h8g(a)4ax.com>, John Larkin wrote: >>On 25 May 2010 10:22:59 -0700, Tim Wescott <tim(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. >>> >>>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 > > Dear John Larkin, > > I like that one! It's notably simple, as in being a DC-to-DC >converter having only 4 components (excluding the often-advised >capacitor across the power supply leads of the IC - .1 uF 25V cheapie >ceramic capacitor is an often-advised occaisionally-necessary item >that gets the component count up to 5, 6 if you also count the LED. > > Component count may get to 6 excluding the LED, 7 including it, if >this boost converter gets good enough to overpower the LED or deliver >more output power than desired, so as to necessitate adding a resistor in >series with the LED. > > I would like to add that efficiency is likely to improve if the non-LED >diode (a reaistor is offered as a workable alternative) is a Schottky one. >I would look into Schottky diodes with breakdown voltage 30V at most, >maybe 20V, and rated to handle 1 amp or less, maybe much less. Come to >think of it, much less to get improvement towards shorter switching times. > > It does appear to me that the shown capacitor and resistor are "left to >the student". I would like to make that capacitor .01 uF merely from >knowing that one is a common cheap part. I could gain desire to make it >smaller in consideration of likely oscillation frequency considering a >desired value for the shown resistor... > > I would want to make that resistor 100K max to "make this cleaner", and >I have a liking to get oscillation frequency into the 50 to >mildly-above-100 KHz ballpark, in order to make the oscillation frequency >ultrasonic to humans and most pets (even though dB acoustic pressure is >impressively low to negligible likely less than 30 1 meter away). > > Also I would want the oscillation frequency to be not-too-close to the >common ones for TV/VCR/DVD common consumer devices. But if the LED emits >at a shorter wavelength, as in/near blue, that is less-likely a problem. > If that problem comes up anyway, I would primarily put a longpass filter >in front of the consumer device sensor - as in Wratten preferably 92, >secondarily 29, tertiarily 25 or equivalents including Schott glass >longpass optical filters (regardless ofwho supplies longpass optical >filters based on Schott glass products), having part numbers starting with >RG and including afterwards 630 to 670. Copy of a scheme by Bob Hirschfeld, at National, 40 years ago... called "The Miser"... ran on a 1.5V cell. ...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: Jim Thompson on 26 May 2010 12:26
On Wed, 26 May 2010 11:19:43 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Wed, 26 May 2010 07:24:46 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >. >. >. > >>Hmmm, neither C may matter. It might all cancel out. Somebody should >>do the math. > >Who better than the designer? > >Besides, that circuit won't work as drawn. Wonder why? Wonder how Larkin will excuse that away ?:-) ...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 |