Timeline for How can I efficiently drive an LED?
Current License: CC BY-SA 3.0
38 events
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| Dec 13, 2017 at 19:23 | comment | added | e-motiv | Great answer. Would be even greater if the total cost of each solution would be stated. Not really asked, but why not? It would fit the wonderful answer. ;) PS what would the efficiency be for the given current source for only 1 led? Probably much less.Then what would be a more efficient design for 1 led withoutswitching? | |
| Dec 6, 2017 at 14:10 | comment | added | Phil Frost | @LongLog Sounds like a good question: electronics.stackexchange.com/questions/ask | |
| Dec 5, 2017 at 16:38 | comment | added | LongLog | (regarding SMCS, sorry) | |
| Dec 5, 2017 at 14:50 | comment | added | LongLog | Can this also be done with a (polarized or not) capacitor? | |
| Apr 13, 2017 at 12:32 | history | edited | CommunityBot |
replaced http://electronics.stackexchange.com/ with https://electronics.stackexchange.com/
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| Jan 17, 2017 at 13:32 | comment | added | Phil Frost | @JulienFr I doubt it: the internal resistance of an AA battery is too high for it to provide 10W. Maybe ask a new question if you want more information? | |
| Jan 14, 2017 at 18:16 | comment | added | julienfr112 | Is it possible to do a "straight accross the battery" with a 10W rated led, like this one fr.aliexpress.com/item/… and a AA battery ? | |
| Sep 7, 2016 at 12:46 | comment | added | Phil Frost | @Barleyman I don't see why. The LED current is limited by the duty cycle and the inductance, even if you model this circuit with an ideal inductor with no ESR. It is not possible to attain unlimited current with any inductor, even an ideal one, in a finite time. | |
| Sep 6, 2016 at 21:05 | comment | added | Barleyman | The downside of that SMPS circuit is that the LED current is not actually limited by anything except the inductor resistance. Granted, 1mH probably has big enough ESR that you're not cooking the LED right away but something to keep in mind. A more elegant solution is to use an actual SMPS controller and an opamp feedback to create a true constant current source. Also a fair few switch mode LED controllers exist but what's the challenge in those? And finally, it's non-trivial to adjust the current limit directly so most people use PWM to vary the brightness and keep the current at 100% value. | |
| Sep 6, 2016 at 20:43 | history | edited | Phil Frost | CC BY-SA 3.0 |
fix a few minor typographical and factual errors
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| Oct 28, 2014 at 15:17 | comment | added | Adam Lee | @PhilFrost Thanks, I posted a question - electronics.stackexchange.com/questions/136208/… | |
| Oct 27, 2014 at 19:39 | comment | added | Phil Frost | @b1gtuna, that's a good enough question I think you should ask it as a question of its own so the entire site can participate. You can link to this question or copy the schematics for context. | |
| Oct 27, 2014 at 15:41 | comment | added | Adam Lee | Thx for a thorough answer. In your linear current source example, will the LED turn off once Q1 steals the base current of Q2? | |
| Jun 6, 2014 at 19:32 | comment | added | Phil Frost | @sherrellbc the circuit alternates between those two states very rapidly, and the current shown on the graph is an average. If the current ripple is problematic the addition of a rectifier and filter gets rid of it, and the LED sees only the average current. | |
| Jun 6, 2014 at 19:08 | comment | added | sherrellbc | I don't quite understand the charts you have shown.For example, when Q1 is off the inductor will generate a sufficiently negative voltage at the transistor/inductor node. This will effectively forward bias the diode and consequentially current will flow through the device. When Q1 is on, the current flow through the inductor and shorts the collector of the transistor to ground (thereby 0V exist across the diode). However, your graphs show that at 0V across the diode there exists a 15mA current through the device? | |
| Jun 16, 2013 at 9:16 | comment | added | RedGrittyBrick | See also Joule thief for efficiently driving LEDs from very low voltage sources such as nearly exhausted single-cell batteries. | |
| Apr 17, 2013 at 12:13 | comment | added | Phil Frost | @clabacchio graphs by gnuplot | |
| Apr 16, 2013 at 19:50 | comment | added | clabacchio | @PhilFrost and what did you use for the graphs? | |
| Feb 1, 2013 at 21:21 | history | edited | Phil Frost | CC BY-SA 3.0 |
add links
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| Jan 29, 2013 at 16:51 | history | edited | Phil Frost | CC BY-SA 3.0 |
state the efficiency of switched mode current sources less superlatively
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| Jan 29, 2013 at 15:20 | history | edited | Phil Frost | CC BY-SA 3.0 |
correct language
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| Jan 29, 2013 at 12:59 | history | edited | Phil Frost | CC BY-SA 3.0 |
add links, tweak language
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| Jan 29, 2013 at 2:42 | history | edited | Phil Frost | CC BY-SA 3.0 |
update images
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| Jan 26, 2013 at 18:08 | vote | accept | Phil Frost | ||
| Jan 24, 2013 at 13:35 | history | edited | Phil Frost | CC BY-SA 3.0 |
add illustrations
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| Jan 23, 2013 at 18:59 | history | edited | Phil Frost | CC BY-SA 3.0 |
Link to question on parallel LEDs
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| Jan 23, 2013 at 12:08 | comment | added | Phil Frost | @m.Alin schematics by gschem. | |
| Jan 23, 2013 at 9:31 | history | edited | m.Alin | CC BY-SA 3.0 |
fixed typo
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| Jan 23, 2013 at 9:17 | comment | added | John U | +1 - this post should be sticky or hung in a gallery or something for everyone who ever asks about "how to light an LED" or all the thousands of variations on the same question. | |
| Jan 23, 2013 at 8:34 | comment | added | m.Alin | What's the schematic editor you're using? | |
| Jan 23, 2013 at 8:18 | comment | added | Rev | Nice answer. Maybe the "series resistor" section should also point out, that it is a bad idea to drive multiple parallel LEDs this way. Real world diodes don't have same characteristics and what then happens is that the diode with lowest forward voltage will conduct most of the current and it will wear out the fastest. | |
| S Jan 23, 2013 at 4:26 | history | suggested | Shamtam | CC BY-SA 3.0 |
fixed a typo (current increases exponentially with voltage, not current)
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| Jan 23, 2013 at 4:16 | review | Suggested edits | |||
| S Jan 23, 2013 at 4:26 | |||||
| Jan 23, 2013 at 3:05 | history | edited | Phil Frost | CC BY-SA 3.0 |
minor fixes
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| Jan 23, 2013 at 3:01 | comment | added | Phil Frost | @HikeOnPast that's been covered | |
| Jan 23, 2013 at 2:57 | comment | added | HikeOnPast | There's also inductor-less PWM to limit the thermal load to within the package spec even while driving at a higher peak current than the device continuous rating. Higher perceived brightness for less average power has been claimed by some using this technique. Some sort of current limiting is still required in this case, whether it be battery impedance, series resistor, or current source. | |
| Jan 23, 2013 at 2:33 | history | edited | Phil Frost | CC BY-SA 3.0 |
throwies!
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| Jan 23, 2013 at 2:18 | history | answered | Phil Frost | CC BY-SA 3.0 |