L.E.D forward current measurment

[rajaram04]

Hello sir

If incase we don't have any idea about the forward current ratings for an L.E.D while purchasing or getting it from somebody then how to calculate the maximum required forward current rating ???

 

[tpetar]

I dont know my friend, I see you stuck with these LEDs. :smile:

Sometimes is easier to buy new from catalog with known manufacturer, model ID and good datasheet then to experiment and destroy LEDs on test.

LEDs what you show in previous thread 3mm 5mm or 8mm THT LEDs usually have current ratings 25mA 35mA, not more. Monitor heating of LEDs body and legs on short and long time.

If LEDs are white, supply 3,4V to LED and measure current.

 

[rajaram04]

I dont know my friend, I see you stuck with these LEDs. :smile:

Sometimes is easier to buy new from catalog with known manufacturer, model ID and good datasheet then to experiment and destroy LEDs on test.

LEDs what you show in previous thread 3mm 5mm or 8mm THT LEDs usually have current ratings 25mA 35mA, not more. Monitor heating of LEDs body and legs on short and long time.

If LEDs are white, supply 3,4V to LED and measure current.

hmm seems no other idea we can apply to get results easily . . ok as you say

Well as you told about 3.4 volts earlier so may i apply 3.6 v inplace of it ? or i ll hv to make 3.4 v exactly ???????

 

[tpetar]

You skip first step in electronics to get or make as first project nice small lab power supply. :smile:

If you dont have it, use 6V or 12V battery and voltage regulator LM317 or similar and adjust voltage to your needs.

For short you can try Li-Po or Li-Ion battery which is half empty and shows 3,4V - 3,6V. Even small battery from phone can help you.

 

[rajaram04]

You skip first step in electronics to get or make as first project nice small lab power supply. :smile:

If you dont have it, use 6V or 12V battery and voltage regulator LM317 or similar and adjust voltage to your needs.

For short you can try Li-Po or Li-Ion battery which is half empty and shows 3,4V - 3,6V. Even small battery from phone can help you.

okk what about it ???



i ve this one as a compact hand held

 

[tpetar]

You can try, but for testing current you need more current reserve. This small tiny battery maybe is old and weak to supply needed current and this can give wrong reading in your test.

 

[rajaram04]

You can try, but for testing current you need more current reserve. This small tiny battery maybe is old and weak to supply needed current and this can give wrong reading in your test.

okk sure

so for LM 317 i GOT R1 as 150 ohms & R2 as 258 ohms from the oline calculator

to get this required 3.4 volts as you said

so here is the diagram




so is it ok or any changes we need here ?

 

[tpetar]

Better use potentiometer that you can adjust various voltage.

Easy Adjustable Supply
https://www.ladyada.net/library/equipt/diypsupp.html

 

[rajaram04]

hmm ohh okk

thats a preety cool circuit for me

now let see then how much i can proceed to get all results . . well thanks

 

[tpetar]

Input voltage can be higher then 9V, such as 15V-20V.

If you use transformer with Graetz bridge use higher capacitor values, plus on output add 100nF.

 

[rajaram04]

Input voltage can be higher then 9V, such as 15V-20V.

If you use transformer with Graetz use higher capacitor values, plus on output add 100nF.

okk sure i ll take care of it

well sir a 9 volts battery is shown here so is it a rechargable high current rating one or simple one ??

is it possible to drive LM 317 with normal batteries ?

 

[pranam77]

As LED's are current sensitive devices, testing them with a direct variable power supply or 3.6 volt battery is never recomended. Try searching a constant current source to test led's. Connecting the X led to the tester and measuring the voltage across will give you the 99% perfect forward voltage of a unknown LED. make a small handly circuit shown below to test almost any through hole LED's

 

[tpetar]

okk sure i ll take care of it

well sir a 9 volts battery is shown here so is it a rechargable high current rating one or simple one ??

is it possible to drive LM 317 with normal batteries ?

Can be alkaline or standard, no problem.

 

[rajaram04]

As LED's are current sensitive devices, testing them with a direct variable power supply or 3.6 volt battery is never recomended. Try searching a constant current source to test led's. Connecting the X led to the tester and measuring the voltage across will give you the 99% perfect forward voltage of a unknown LED. make a small handly circuit shown below to test almost any through hole LED's

ohhhhhh i see gr8 work yaar :smile:

nice nice ok i ll proceed as per the diagram

so here X LED means ?

can we connect 5 LEDs parallely at a time as per figure ??????????

 

[rajaram04]

As LED's are current sensitive devices, testing them with a direct variable power supply or 3.6 volt battery is never recomended. Try searching a constant current source to test led's. Connecting the X led to the tester and measuring the voltage across will give you the 99% perfect forward voltage of a unknown LED. make a small handly circuit shown below to test almost any through hole LED's

this circuit is much better option thanks

do you have any kind of it for current measurement ???

please have me a diagram