Volt voltage Ub

Volt LED voltage Uf

mA LED current If

N number of ( serial ) leds
°C temperature Tamb
°C/mW resistor Rth r-a

 


LED resistor

Ohm
    
E24 R

LED resistor

Ohm
     E24 R

LED resistor

mW
     E24 R
LED resistor
°C
     E24 R
LED resistor
°C+
     E24 R

LED current

mA
     E24 R

LED dissipation

mW
     E24 R

LED total dissipation

mW
     E24 R
Total dissipation
mW
    
E24 R
recommended
N max
     6A !
theoretically
N min
     6B !


E24 series :

10 11 12 13 15 16 18 20 22 24 27 30
33 36 39 43 47 51 56 62 68 75 82 91.
 
resistor colour code
 


This script calculates the value of the LED resistor ( and the E24 equivalent, colour code included ) : the required serial resistor with one LED or more LEDS in a chain

1 - Type the available voltage Ub.

2 - Type the characteristic LED voltage Uled, Uf : according to the datasheet.

3 - Idem for the LED current Iled, If.

4 - ( A ) Give in the number of LEDS.
     ( B ) Give in ( if you want ) the temperature Tamb and the resistor Rth r-a ( Rth c-a ), the so called thermal resistance.

For example : Ub = 10 Volt, LED voltage = 2 Volt, LED current = 15 mA, 2 serial LEDS => you find the correct E24 value and the colour code. 430 Ohm yellow orange brown.

5 - ( A ) You find a value ( unrounded ) in Ohm : the calculated serial resistor.
     ( B ) You find a value in Ohm : the E24 version. It can be equal to the value of the first resistor. Or it will be rounded up.
     ( C ) You find the E24 resistor and LED diode values of current and dissipation. Also total dissipation ( concerning the resistor and all the LEDS ) is given. Of course this JS calculates via the E24 resistor value ( E24 R ) ..... if this is unwanted, see here Also you find the temperature increase and resulting temperature of the resistor body.

6 - ( A ) Exclusively intended for real experts : you find a recommended maximal number ( N max ) of LEDS. Unfortunately a lot of misunderstandings exist concerning. Here we have applied an average and rounded ( up ) value of 2/3 ( calculation level critical ). Of course, you can take still less LEDS in combination with a larger resistance. If you think that it will be more safe.
     ( B ) You also find a minimal number of LEDS ( N min ). Theoretically, now, a resistor is no longer necessary for the limitation of the current. Possibly, the number of LEDS can be extended a little bit to realize lower values of Uf ( and If ). However, in any case, pay attention well to the current If as long as you use a voltagesource ! Actually, in such cases a currentsourse is recommended, for example, see here

This is the simple basic formula, concerning the calculation of the serial resistor R = ( Ub - Uf ) / If

7 - The Reset System button clears the outputs and sets defaults again.