Info in the link (LED related)

[rajaram04]

Hello sir

here is a link i got

https://www.instructables.com/id/Choosing-The-Resistor-To-Use-With-LEDs/


Is the information all correct here ? please check

 

[betwixt]

Looks correct but it's really a lot simpler than that. The resistor formula is:

Resistor value = (Source voltage - LED voltage) / LED current.

Voltage measured in Volts, current measured in Amps and resistance measured in Ohms. So for example, with a 12V adapter, a 1.6V LED and current of 15mA (0.015A): R = (12 - 1.6) / 0.015 = 693 Ohms.
As that isn't a standard value, you can either make it up for combinations of resistors or just pick the nearest value of 680 Ohms.

Brian.

 

[Audioguru]

The Instructable must be old. Modern very bright green LEDs have been available for at least 12 years and are made exactly the same as blue and white (he called then while) LEDs and are also 2.8V to 3.8V.

The very cheap looking power supply says 12VDC but it is not regulated. Then when it has a low current load it might be 18V or more.

 

[rajaram04]

The Instructable must be old. Modern very bright green LEDs have been available for at least 12 years and are made exactly the same as blue and white (he called then while) LEDs and are also 2.8V to 3.8V.

The very cheap looking power supply says 12VDC but it is not regulated. Then when it has a low current load it might be 18V or more.

ya ya i had a doubt with that 12 volts supply which is much much better that i designed as per your directions

So for modern bright LEDs is it a better idea (as per suggestion in the link) to choose 25mA as avg.value for an unknown LED ? ? ?

- - - Updated - - -

Looks correct but it's really a lot simpler than that. The resistor formula is:

Resistor value = (Source voltage - LED voltage) / LED current.

Voltage measured in Volts, current measured in Amps and resistance measured in Ohms. So for example, with a 12V adapter, a 1.6V LED and current of 15mA (0.015A): R = (12 - 1.6) / 0.015 = 693 Ohms.
As that isn't a standard value, you can either make it up for combinations of resistors or just pick the nearest value of 680 Ohms.

Brian.

hmm i applied same formula & got similiar results like you told above

ok sir thanks for the info once again

 

[Audioguru]

When the supply voltage is very high (12V) and the LED voltage is very low (1.6V) then the current does not reduce much when the red LED is actually 2.2V.

 

[rajaram04]

When the supply voltage is very high (12V) and the LED voltage is very low (1.6V) then the current does not reduce much when the red LED is actually 2.2V.

hmm means these red LEDs have issues with power patameters & thats the reason i blewed too much of them in my experimental carrier

 

[Audioguru]

12V supply:
When the red LED is 1.6V then the resistor to limit the current to 20mA is (12V - 1.6V)/20mA= 520 ohms. If you use a standard 510 ohms then the current is (12V -1.6V)/510 ohms= 20.4mA.

But if the LED or another red LED is actually 2.2V then with the 510 ohms resistor its current is (12V - 2.2V)/510 ohms= 19.2mA.

20.4mA and 19.2mA will look like the same brightness. The current is low enough to allow the LEDs to last for a long time.
If you blew up many LEDs then either the current was too high or they were cheap and low quality.

 

[rajaram04]

12V supply:
When the red LED is 1.6V then the resistor to limit the current to 20mA is (12V - 1.6V)/20mA= 520 ohms. If you use a standard 510 ohms then the current is (12V -1.6V)/510 ohms= 20.4mA.

But if the LED or another red LED is actually 2.2V then with the 510 ohms resistor its current is (12V - 2.2V)/510 ohms= 19.2mA.

20.4mA and 19.2mA will look like the same brightness. The current is low enough to allow the LEDs to last for a long time.
If you blew up many LEDs then either the current was too high or they were cheap and low quality.

12V supply:
When the red LED is 1.6V then the resistor to limit the current to 20mA is (12V - 1.6V)/20mA= 520 ohms. If you use a standard 510 ohms then the current is (12V -1.6V)/510 ohms= 20.4mA.

But if the LED or another red LED is actually 2.2V then with the 510 ohms resistor its current is (12V - 2.2V)/510 ohms= 19.2mA.

20.4mA and 19.2mA will look like the same brightness. The current is low enough to allow the LEDs to last for a long time.
If you blew up many LEDs then either the current was too high or they were cheap and low quality.

naaa i guess current was high as i was unable to choose proper resistor with power supply parameters

LEDs were ok as many of them are commonly used for bog projects work here & all are working fine for last 10 years

 

[Audioguru]

Of course your LEDs will burn out if you did not MEASURE the power supply voltage and you used the wrong resistor values.

 

[rajaram04]

hmm ya as you explained all earlier now i'd take precautions at every moment . . thanks