white led

[audioguru2]

Hi Pier,
I think a transformer is designed to allow a 10% mains over-voltage.

 

[pier1]

Hi AG
        In my previous LED project 2 LED's blew off from in between the string , I think that the quality of the LED is poor . What do u think ? . I just replaced them .

 

[audioguru2]

Are your LEDs manufactured by a major semiconductor manufacturer?

 

[pier1]

No AG, its a chineese make.

 

[audioguru2]

No AG, its a chineese make.

Hee, hee, hee. ;D ;D ;D

I bought a bag of 100 LEDs made by Fairchild. Every one is absolutely perfect and they were a pretty good price.

 

[pier1]

Do you have the part number to order for the led's made by fairchild . What price you bought it for ?

 

[audioguru2]

Fairchild and all the other major semiconductor manufacturers make hundreds of excellent LEDs at a good price. I recently got an e-mail from the distributor where I bought mine that mine are now discontinued and I could have bought the last ones they had. I didn't buy any more because better ones are available now.

I bought some white and blue LEDs made by Hewlett-Packard who changed to Agilent who changed to another name. They are made for pixel screens at stadiums and are also excellent.

I bought some LEDs made in your country and half of them were bad. The store replaced them all with better ones.

I bought some LEDs made in the same country as ypurs. Most were good but some  failed.

 

[ante1]

Hi AG
        In my previous LED project 2 LED's blew off from in between the string , I think that the quality of the LED is poor . What do u think ? . I just replaced them .

As with transistors in parallel you can

 

[pier1]

will i be able to get LED's which are similar to each other, i mean from big branded manufacturers ? something like led's from a batch ?

 

[audioguru2]

Hi Pier,
Aren't your LEDs connected in series? Then the current through each one is exactly the same and the LEDs don't need to be the same. They just need to live up to their current rating.

I bought my factory-sealed bag of 100 Fairchild LEDs online from Digikey. They were probably from the same batch.

 

[pier1]

Hello AG
            What was the part number you gave ?

 

[audioguru2]

My bright red wide-angle LEDs are these ones:

MV8191.pdf

 

[pier1]

In one of their page (pdf) i found white with the part number : 'MV8W0O'
http://www.fairchildsemi.com/collateral/psg04_opto.pdf#page=28

 

[audioguru2]

Fairchild's MV8W00 white LED is narrow angle and is not as bright as modern LEDs.
Digikey don't have any in stock so maybe it is not made anymore.

Fairchild's website has old catalogs like the one you found.
I don't think Fairchild makes LEDs anymore.

 

[pier1]

Hi AG
        Which manufacturer would be your next choice ?

 

[audioguru2]

I used Hewlett-Packard's LEDs for many years. Then their opto business was sold to Agilent who sold it to Avago. Digikey sell these excellent Avago LEDs at a pretty good price.

There are forums for guys who eat and breath LEDs. They talk about the good and new brands of LEDs better than me.

 

[pier1]

While testing the board (old project with 52 led's) i applied just about +50 volts and found all the LED's start to work with a very dim light but around 4 of them were very very dim than the other 48 ones which were uniform in brightness. Is this because of the forward voltage rating or will those 4 of them fail fast ?

 

[audioguru2]

If the LEDs are in series and are the same make then they should all be the same brightness because in series the all have the same current. I guess your dim ones are not good.

 

[pier1]

I fixed them with good ones, but the capacitors are still charged even after the led's are off . They give small shocks . I took the pcb in my hand after the led's were off, thinking they would be discharged .

 

[audioguru2]

Shocking!
A white LED can have about 2.5V across it and not pass any current.
You have 70 LEDs in series? Then the capacitor will be charged to at least 175V which will bite you.