LED and heat

Discussion in 'General Electronics Chat' started by Zanac-X, Sep 8, 2012.

Dec 23, 2011
51
1
hey guys

i have a regular LED (30 mA, 3.6 v) and im trying to get the max bright and of course with max efficiency (less heat) so i connected it with a 4.5 volt (3 AA battery) and got the best of it but when i used the 9v battery i got the same glow but the much more heat in the LED so that got me thinking how much can the LED live on a 9v battery and a 4.5 net battery and is it ok to use the 9v keeping in mind that the whole circuit is just the LED

thanks

2. stanman11 Member

Nov 23, 2010
230
4
as long as you have a resistor it should be ok but you really dont need all that power so you need to figure out the max rating with what resistor you need

3. panic mode Senior Member

Oct 10, 2011
1,330
305
limit current to whatever LED is rated for and you can use any voltage...

Apr 5, 2008
15,806
2,389
Hello,

Always use a resistor to limit the current.
You can calculate it using the following formula:
Rlimit = (Vsupply - (number of leds * Voltage of leds))/wanted current
For example:
Vsupply: 9 Volts
Number of leds: 2 (in series)
Voltage of leds: 3.6 Volts
Wanted current: 20 mA
Rlimit = (9 - (2 * 3.6)) / 0.02 = (9 - 7.2) / 0.02 = 1.8 /0.02 = 90 Ohms.
Choose the next higher value to have a safe (lower) current.
The next higher value in E24 is 91 Ohms.
The next higher value in E12 is 100 Ohms.

Bertus

Zanac-X likes this.

Dec 23, 2011
51
1
thanks very much that was more than helpful but one thing left :

you said "wanted current" so dose that mean i can supply any current below the max forward current (in my case 30 mA) ?

and if i do would it effect the brightness of the LED

thanks

Last edited: Sep 9, 2012

Apr 5, 2008
15,806
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Zanac-X likes this.
7. stanman11 Member

Nov 23, 2010
230
4
didfferent LED's have different micro candls MCD. 1000mcd is 1candle.
correct me if im wrong

Apr 5, 2008
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9. ScottWang Moderator

Aug 23, 2012
4,934
777
When we using a LED, always focus on the current, because the voltage is almost constant, but the current is adjustable from 0 to Imax, as your LED current is 30mA.

When I using the LED, always set the current around or below 80% of LED, but almost use it below 80%, when we add about 70% of the Imax current to the LED, almost reach to the high brightness, if we using it over 70% of Imax, it won't increase much brightness, but if we add it over 80% to 100%, it will reduce the LED life, it will also reduce the Luminous efficacy of LED.

For example :