Basic LED Questions
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 17th December 2003, 06:21 PM #11 Magura   diyAudio Member     Join Date: Oct 2003 Location: Denmark, Viborg All this calculating resistor stuff is ok....but the easy way in most cases is to use a driver. A LED driver will cost you 0.2usd, and you can even run it with current feedback in order to maintain the correct intesity of the LED. Add an LDR to the circuit, and you got a LED array that compensates for the ambient light. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com
jean-paul
diyAudio Moderator Emeritus

Join Date: Sep 2002
Location: Germany
Quote:
 Originally posted by Magura All this calculating resistor stuff is ok....but the easy way in most cases is to use a driver. A LED driver will cost you 0.2usd, and you can even run it with current feedback in order to maintain the correct intesity of the LED. Add an LDR to the circuit, and you got a LED array that compensates for the ambient light. Magura

What's the use of a LED driver ( ? ) if a resistor is enough ?

BTW I made the mistake myself to think a resistor is *always* needed. I searched for the thread about blue LEDs directly wired to a newly wound winding on a toroid ( P.Daniel ) but I didn't find it. When the LED is operated in the right spot in its curve ( supply voltage just above turn-on voltage of the LED ) a resistor can be omitted but it is really wiser to use one in all cases for safety reasons. I would measure first if you have 2.4 V exactly. When it is higher you certainly need the resistor.

When you want to feed the LED from a low voltage AC winding as the suggested extra winding I would use a series resistor and a series diode like a BATxx type ( Uf of 0.2 V ). LED's don't like reverse voltages too much.

http://www.diyaudio.com/forums/showt...=&pagenumber=4
__________________
It's only audio. Member of the non modular PCB design committee

 17th December 2003, 09:37 PM #13 lgreen   diyAudio Member     Join Date: May 2003 Location: San Diego, USA What about Question#2? Thanks for the posts, but what about question #2? What is the best way to turn off the LED, open circuit or short both ends to ground?
millwood
Account Disabled

Join Date: Apr 2003
Location: US
Quote:
 Originally posted by jean-paul I would use a series resistor and a series diode like a BATxx type ( Uf of 0.2 V ). LED's don't like reverse voltages too much.
I would use a diode (any diode) in parrallel with the LED but in opposite directions. LEDs usually have a reverse voltage of 4-5v. so your method would also work as the overwhelming majority of the reverse voltage will be on the diode, not the LED. but I just feel safer knowing my LEDs aren't hugely reversely biased.

Richard C
diyAudio Member

Join Date: Jul 2003
Location: Nottingham, England

Quote:
 Originally posted by lgreen What is the best way to turn off the LED, open circuit or short both ends to ground?
Open-circuit.

Magura
diyAudio Member

Join Date: Oct 2003
Location: Denmark, Viborg
Quote:
 Originally posted by jean-paul What's the use of a LED driver ( ? ) if a resistor is enough ?

Since a LED dosnt maintain the same intensity over the years, a driver with current feedback will compensate for this. Just take a look at older LED signs, the intensity matching simply sucks.

Thats part of the point of using a driver, but especially if you run more than 1 LED, id say a driver is a must. You could buy intensity matched LED's, but at a fairly high price, and with a limited time horisont of the matching anyway.

Magura
__________________
Everything is possible....to do the impossible just takes a little while longer.
www.class-a-labs.com

 18th December 2003, 08:05 PM #17 Richard C   diyAudio Member   Join Date: Jul 2003 Location: Nottingham, England A constant current driver won't compenste for an LED dimming due to ageing unless the reduction in luminence is due only to increased forward-voltage.
 18th December 2003, 08:09 PM #18 Magura   diyAudio Member     Join Date: Oct 2003 Location: Denmark, Viborg Wich it is as far as i know....am i right on this one?? All i know for sure is that it works(keeping the intesity at level using a driver with current feedback). Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com
 18th December 2003, 08:23 PM #19 Richard C   diyAudio Member   Join Date: Jul 2003 Location: Nottingham, England Take an LED with Vf=2V powered from a 12V supply via a 500 Ohm resistor for a current of 20mA. If Vf were to increase by 25% to 2.5V (unlikely) the current would only decrease to 19mA, there would be no perceivable decrease in brightness.
 18th December 2003, 08:27 PM #20 Magura   diyAudio Member     Join Date: Oct 2003 Location: Denmark, Viborg Hmm...will have to investigate what actually happens when a LED grows old and looses intensity. I guess this could be done by over-powering a LED for a couple of hours. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post wigginjs Multi-Way 8 20th October 2004 08:22 PM jlh28 Everything Else 1 12th January 2004 01:49 AM DarkMage Multi-Way 2 5th November 2003 03:51 PM Ziller Everything Else 5 13th January 2002 03:49 PM wnichol Solid State 4 16th November 2001 05:59 AM

 New To Site? Need Help?

All times are GMT. The time now is 01:04 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.