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Topic: LEDs without the use of current limiting resistors (Read 5 times) previous topic - next topic

Boffin1

Quote
Because both statements ("you have to use a resistor" and "you cannot use resistors") are wrong. Whether you should use a resistor or not is application specific and needs to be evaluated specifically.

Just common sense.


exactly,  you dont need a resistor with a constant current driver for example, but something should limit the current to the manufacturers recommendations, common sense.
With my mobile phone I can call people and talk to them -  how smart can you get ?

Headroom

Interesting thread and a very good example why accidental success does not result in true knowledge.

An LED needs a constant current supply, there is no way around that. Thats based on not too complicated and widely published physics. Perhaps that currnt limit can be achieved by some implicit resistance of the components involves, e.g the internal resistance of a battery etc.

However, the question is whether one would want to base a sound design on something that is more a byproduct of a statistically distributed manufacturing process thats only monitored within rlatively wide limits or a design goal kept within close tolerance. A battery for example is a supplier of electrical energy with the usual design goals  being a stable voltage over time and mAh etc. The internel resiststance is what you get with it and it may not even be stated on a data sheet.

A resistors design goal, however, is to have a specified resistance and can be bought at different tolerance ratings. Using components for their intended purpose is obviously more a sound approach. That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.

retrolefty


Interesting thread and a very good example why accidental success does not result in true knowledge.

An LED needs a constant current supply, there is no way around that. Thats based on not too complicated and widely published physics. Perhaps that currnt limit can be achieved by some implicit resistance of the components involves, e.g the internal resistance of a battery etc.

However, the question is whether one would want to base a sound design on something that is more a byproduct of a statistically distributed manufacturing process thats only monitored within rlatively wide limits or a design goal kept within close tolerance. A battery for example is a supplier of electrical energy with the usual design goals  being a stable voltage over time and mAh etc. The internel resiststance is what you get with it and it may not even be stated on a data sheet.

A resistors design goal, however, is to have a specified resistance and can be bought at different tolerance ratings. Using components for their intended purpose is obviously more a sound approach. That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Yes Sir, you state the case well, no further explanation required.

Lefty

Boffin1

Quote
That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Right, and the whole point of Arduino is to simplfy things for beginners, no direct port manipulation for example, so lets stick to the basics on the hardware side when newbies are asking if a resistor is required  for an LED.
With my mobile phone I can call people and talk to them -  how smart can you get ?

Hippynerd


Quote
That does not mean that you can't get away with not using that approach occasionally. Using that approach, however for a reliable solution is dangerous.


Right, and the whole point of Arduino is to simplfy things for beginners, no direct port manipulation for example, so lets stick to the basics on the hardware side when newbies are asking if a resistor is required  for an LED.


Now I know what the ugly stepchild feels like.  Lets hide him in the closet when company comes to visit. sigh.

So, the next time someone specifically asks:
"LEDs without the use of current limiting resistors"
And gives a very specific example, we are supposed to tell them that its impossible to do that, and they should never think such dangerous thoughts?

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