Terryz_ Posted February 12, 2013 Share Posted February 12, 2013 I have a 5v power supply, can I use it to run a LED emitter that only require 3.5v? Does the Amp play a part powering the LED? Only 1 LED emitter.. Quote Member of: Link to comment Share on other sites More sharing options...
Jameshong Posted February 13, 2013 Share Posted February 13, 2013 I have a 5v power supply, can I use it to run a LED emitter that only require 3.5v? Does the Amp play a part powering the LED? Only 1 LED emitter.. Yes. less amp, less brighter...PAR affected. Insufficient amp to LED spec requirement, it will not turn on. Quote Knowing is not enough; we must apply. Willing is not enough; we must do. - Goethe Link to comment Share on other sites More sharing options...
Terryz_ Posted February 16, 2013 Author Share Posted February 16, 2013 Is there any problem with using a 5v power supply to run a 3.5v led emitter.. Will it shorten the life span of the led? Quote Member of: Link to comment Share on other sites More sharing options...
sherman Posted February 16, 2013 Share Posted February 16, 2013 Confirm have problem. LED need constant current . Using a 5 v power , your current will change when the temperature of your LED change. Quote 6.5 * 2 * 2 + 3.75 * 1.5 *1.5,(Decomn on 14/9/08) 4*2*2 + 2.5*1.25*1.25 (Decomn on 1/8/09) 5*2*2 (Fully LED light system, 140 3 watt SSC leds with 60 degree lens)(Decomm) 2.5*2*2(Fully LED Light System,96 3 watt SSC leds with 60 degree lens)(Decomm) 5*2.5*2(LED only) Eheim return 1 * pump 1 HP Daikin compressor with cooling coil 2 Jebao OW40, 1 ecotech MP40, 1X6085 Tunze wm, 1 CURVE 7 Skimmer 1 DIY 80 led control by Bluefish mini 1 radion XR30W G2, 2 Radion XR15G3 Sump area lite by 5 ft T5 , 6 * SSC 3 watt red LED for refugium 1 Full spectrum E27 led light 1 CR control by bubble count Start No Water Change since 1st Dec 2016 Add new 2.5x2x 1.5 ft [/quote] Link to comment Share on other sites More sharing options...
SRC Member SunkistC Posted February 17, 2013 SRC Member Share Posted February 17, 2013 LED rating of 3.5V means it requires a forward biasing voltage of at least 3.5V in order to turn it ON. Any voltage above 3.5V is OK as long as you put a proper current limiting resistor in series. The voltage drop across the LED is fixed at 3.5V so if you are using a 5V supply, the voltage across the series resistor will be 1.5V If the operating current of the LED is 20mA, the series resistor value should be 1.5V/20mA = 75 Ohm. If you use a series resistor value <75 Ohm, the current will be higher and the LED will be brighter but it will shorten the life span of the LED. If you use a series resistor value >75 Ohm, the current will be lower and the LED will be less bright but it may not shorten the life span of the LED. When LED manufacturer rate the LED at 3.5V, 20mA, life span 20000 hours, they are just stating that the Mean-time-to-failure is 20000 hours when you operate the LED at 3.5V, 20mA. Quote Link to comment Share on other sites More sharing options...
sherman Posted February 17, 2013 Share Posted February 17, 2013 Remember to take care of the relationship between temperature and resistance These are dymanic and not static. So you need a real good feedback circuit to keep your current constant Quote 6.5 * 2 * 2 + 3.75 * 1.5 *1.5,(Decomn on 14/9/08) 4*2*2 + 2.5*1.25*1.25 (Decomn on 1/8/09) 5*2*2 (Fully LED light system, 140 3 watt SSC leds with 60 degree lens)(Decomm) 2.5*2*2(Fully LED Light System,96 3 watt SSC leds with 60 degree lens)(Decomm) 5*2.5*2(LED only) Eheim return 1 * pump 1 HP Daikin compressor with cooling coil 2 Jebao OW40, 1 ecotech MP40, 1X6085 Tunze wm, 1 CURVE 7 Skimmer 1 DIY 80 led control by Bluefish mini 1 radion XR30W G2, 2 Radion XR15G3 Sump area lite by 5 ft T5 , 6 * SSC 3 watt red LED for refugium 1 Full spectrum E27 led light 1 CR control by bubble count Start No Water Change since 1st Dec 2016 Add new 2.5x2x 1.5 ft [/quote] Link to comment Share on other sites More sharing options...
Terryz_ Posted February 17, 2013 Author Share Posted February 17, 2013 Thanks all.. I kinda of get it already.. Quote Member of: Link to comment Share on other sites More sharing options...
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