USB to power special LED's

[roltex_rohit123]

hi guys i've got LED lights used in LED torch now a days. these lights lit up very brightly on my 4.1 volts Li-ion battery. but i doubt whether 5 volts from USB would blow it off. so i wanted to give it a bit protection to prevent this. Is there a need for adding resistance in series to the lights? moreover these lights cannot be connected in series. I was actually surprised to see this. could aby one help?

 

[Hero999]

Yes, you should always add a resistor.

It's also possible that the current was exceeding the maximum rating when they were powered from the Li cell which would cause them to overheat if they were left connected for too long.

 

[roltex_rohit123]

Yes, you should always add a resistor.

It's also possible that the current was exceeding the maximum rating when they were powered from the Li cell which would cause them to overheat if they were left connected for too long.

but i didnt add resistor to the light when they were connected in parallel (3) to a single Li-ion cell. here in laptop usb i am trying to use them for lighting in the dark to see keys. i shall be connecting about 10 led's in parallel. this will give me a very bright light. in just 2 LED's i was able to recognize colours in my room. in three LED's it was like a 8 watt CFL. hope it doesnt exceed the USB current Limit. what resistor cn i use? i think 50 ohm to 100 ohm would be enough

 

[Reloadron]

hope it doesnt exceed the USB current Limit. what resistor cn i use? i think 50 ohm to 100 ohm would be enough

I think you should read the USB specification before you try using the USB ports as a voltage/current source. Before you even begin to worry about what resistor to use you just might want to get an understanding of how much 5 volt current is available from a USB port before really bad things happen.

Ron

 

[roltex_rohit123]

i surfed the net for it and found that the normal current is 100ma. i dont know how much does each LED draw, but they give much light!! i dont want to draw more than 100ma fro the LED's. i would reduce the number of lights if current requirement is more.

 

[Reloadron]

It was just a word to the wise as I have seen USB ports destroyed in the past. They actually do make small USB lamps for use with laptops.

Ron