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LED Questions

Terryz_

By Terryz_,
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Jameshong Newbie

Jameshong

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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.

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Knowing is not enough; we must apply. Willing is not enough; we must do. - Goethe

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sherman Enthusiast

sherman

Posted
Posted

Confirm have problem. LED need constant current . Using a 5 v power , your current will change when the temperature of your LED change.

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 

 nLekOfpYts.jpg
[/quote]


 

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SunkistC Enthusiast

SunkistC

Posted
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Posted

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. :)

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sherman Enthusiast

sherman

Posted
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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

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 

 nLekOfpYts.jpg
[/quote]


 

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