4.5v to 3.8v led help

[oram]

Hi folks. I'm new here.

I am use U.V Led's a lot and would like some help optimizing their performance and limiting how much i seem to blow them.

I usually only have them on intermittently but sometimes they are on for a few minutes or so.

I've been running them at 4.5v based on this as they do blow but not as often, bad practice i know. 3volts just doesn't give me the brightness i would like.

I would like to be able to use a 4.5 volt power supply but reduce the volts to 3.8 volts. As this is the forward current voltage of the led, absolute max is 5v (they blow quick here).

Here is the led's data.

Electrical optical characteristics:

Dc forward ... min 2.8 max 3.8
Dc Reverse ...max 10

Absolute max rating

Dc forward current 30mA
Pulse forward current 100mA

Thanks for any help, I did try to do some googling but didn't know exactly what kind of circuit i need.

Darren

[Pauldf]

A bog standard silicon diode drops somewhere around 0.7v forward biased

[piratepaul]

Confused, these are LEDs, a silicone diode is not ( don't know what LEDs are made of I must admit). Is this a trick question?
LEDs tend to drop about 2v, different types different drop.
Need more spec, don't understand spec stated, where did you get them give me a component number or link.
Do you understand the need for a resistor in series with the LED...( or a junction transistor... or... etc)?
What level of electronics knowledge do you have, may be I don't know, maybe you have a PhD,maybe, maybe etc.

Maybe pass, maybe not, watch your eyes, wear protective eye wear, welding goggles...

Tar&stuff.

[piratepaul]

Possible radiation caution.

Tar&stuff.

[Pauldf]

Sorry for not being clear,
If you have a 4.5v supply and want to drop it to 3.8v then I don't see why you can't connect a silicon diode in series with the circuit after the supply, this ought to drop the voltage to around 3.8v without getting technical.

[oram]

Hi folks.

I can be clear. I have very limited knowledge, i can read schems, have a basic knowledge of how components work. I tend to to plug things into a bread board and see what works and doesn't. I know this is bad practice but I really struggle with theory. I mainly focus on audio electronics for artwork, i use u.v leds to highlight certain inks and at the same time manipulate audio circuits.


I don't understand the need for a resistor in series, i would like to know, I will google search.

here is the link to the component from rapid. http://www.rapidonline.com/Electronic-C ... ed-55-1835

Radiation Caution?

Pauldf.... would i put the silicon diode after the + input then onto the circuit? Is there a specific diode I should use? No apology neccessary, just took me a while to get back on here.

Thanks everyone for your help.

[David]

The important thing with LEDs of any description is not to exceed the current rating - the supply voltage is not really critical as a series resistor is all that is needed to control the current through the LED. The 30 mA rating you quote will be the continuous figure, and the 100 mA is a pulse rating (i.e. not continuous), where there is time for the LED to dissipate the heat which it will generate. There is a very useful calculator on this site which will give you the values of the series resistor for any supply voltage (see under calculators).

[oram]

Thanks David. Just looking at the calculator now.

I'm a little confused though, could i then lets say have a 9volt power supply run the led's? and would a series resistor stop it from burning up?

Thank you

[oram]

Got hold of the correct diode, with the right forward voltage drop. Does exactly what i needed. Thanks. This forward voltage diode trick is gonna be useful.

[David]

Yes, with the correct series resistor you could run the LEDs from virtually any voltage