Blue LED at 3.3V
in [Design]
|
From: Phil Hobbs on 26 May 2010 21:36 Jim Thompson wrote: > 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 Might need a cap at the input, but otherwise OK, I think. If you make the resistor big enough, the input capacitance of the inverter should make it work fine. Nice low parts count. 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 net http://electrooptical.net
From: Jim Thompson on 26 May 2010 21:52 On Wed, 26 May 2010 21:36:02 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >Jim Thompson wrote: >> 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 > >Might need a cap at the input, but otherwise OK, I think. If you make >the resistor big enough, the input capacitance of the inverter should >make it work fine. Nice low parts count. > >Cheers > >Phil Hobbs I think you'd need to tailor the rate to accommodate the source/sink capability of the inverter (not shown, bubble to be imagined :-) ...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: Phil Hobbs on 26 May 2010 21:55 Jim Thompson wrote: > On Wed, 26 May 2010 21:36:02 -0400, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> Jim Thompson wrote: >>> 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 >> Might need a cap at the input, but otherwise OK, I think. If you make >> the resistor big enough, the input capacitance of the inverter should >> make it work fine. Nice low parts count. >> >> Cheers >> >> Phil Hobbs > > I think you'd need to tailor the rate to accommodate the source/sink > capability of the inverter (not shown, bubble to be imagined :-) > > ...Jim Thompson Urinating contests aren't my cup of tea. ;) 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 net http://electrooptical.net
From: Spehro Pefhany on 26 May 2010 22:01 On Wed, 26 May 2010 21:36:02 -0400, the renowned Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >Might need a cap at the input, but otherwise OK, I think. If you make >the resistor big enough, the input capacitance of the inverter should >make it work fine. Nice low parts count. > >Cheers > >Phil Hobbs A typical blue LED won't actually be off with a Si diode in series and 3.3V, even without considering temperature and tolerance on the 3.3V. Can be fixed with two Si diodes in series the way I drew it (but even that might be a bit marginal) or use a red LED for the diode. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Jim Thompson on 26 May 2010 22:24
On Wed, 26 May 2010 21:55:56 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >Jim Thompson wrote: >> On Wed, 26 May 2010 21:36:02 -0400, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> Jim Thompson wrote: >>>> 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 >>> Might need a cap at the input, but otherwise OK, I think. If you make >>> the resistor big enough, the input capacitance of the inverter should >>> make it work fine. Nice low parts count. >>> >>> Cheers >>> >>> Phil Hobbs >> >> I think you'd need to tailor the rate to accommodate the source/sink >> capability of the inverter (not shown, bubble to be imagined :-) >> >> ...Jim Thompson > >Urinating contests aren't my cup of tea. ;) > >Cheers > >Phil Hobbs But John "I left out the bubble" Larkin makes it so-o-o-o easy ;-) I think he's the one going senile. He claims it's me, but I feel (and think) like an 18 year old :-) ...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 |