Blue LED at 3.3V
in [Design]
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From: whit3rd on 26 May 2010 14:33 On May 25, 10:18 am, rich <rsoennich...(a)gmail.com> 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. Wherever you got your 3.3V from, there's probably OTHER power available. Use that. Regulated 3.3V power is unsuitable for this task. If that's blocking you, re-engineer it so it doesn't.
From: John Larkin on 26 May 2010 14:48 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? I have a day job. An idea isn't a design. > >Besides, that circuit won't work as drawn. Why not? The schmitt needs to be an inverter to oscillate of course, but that should be obvious to anyone who posts to s.e.d. The point is that a clock, a cap, and a diode will boost 3.3 volts nicely, to drive a 3 volt LED. One could even eliminate the resistor! Better than any ideas you or JT posted. C'mon, do us a 555 thing. Or something with 85 transistors. John
From: Jim Thompson on 26 May 2010 17:09 On Wed, 26 May 2010 11:48:28 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >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? > >I have a day job. An idea isn't a design. > >> >>Besides, that circuit won't work as drawn. > >Why not? The schmitt needs to be an inverter to oscillate of course, >but that should be obvious to anyone who posts to s.e.d. The point is >that a clock, a cap, and a diode will boost 3.3 volts nicely, to drive >a 3 volt LED. One could even eliminate the resistor! > >Better than any ideas you or JT posted. C'mon, do us a 555 thing. Or >something with 85 transistors. > >John > Excuses! Excuses! Excuses! Inverter or buffer, it can't work as drawn. Your day job certainly isn't circuit design :-) ...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: David Eather on 26 May 2010 17:56 On 27/05/2010 12:31 AM, George Herold 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. > > > > > Thanks.
From: Jim Thompson on 26 May 2010 17:59
On Thu, 27 May 2010 07:56:08 +1000, David Eather <eather(a)tpg.com.au> wrote: >On 27/05/2010 12:31 AM, George Herold 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. >> >> >> >> >> >Thanks. Theory of "operation" is left as an exercise for the student :-) ...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 |