1n4001

[fkuk]

i need to light up 9 LEDs

the forward voltage is between 3.4V and 3.6V

and they are all wired up in parralel



i have a 12V power supply connected to a LM323T (5V 3A voltage regulator)

and to reduce the voltage from 5V to 3.6V i have used 2 1N4001 diodes in series to do this (.7V x2)

the total current i have mesured is .88A and .99A

this setup works on the bench and nothing seems to get hot

but i want to know how stable the diodes are doing this job, as these leds will be mounted at the front of a car

 

[Reloadron]

Actually placing all the LEDs in parallel isn't the best way to go about this. You would do better to run off the 5 volt regulator but skip the voltage dropping diodes. The suggested method would be to place a series resistor on each LED then parallel them. The problem with just placing the LEDs in parallel, even though they are the same is in reality some will tend to conduct harder than others. Thus when LEDs are in parallel a series resistor with each is the preferred method. That will ensure a longer better LED life.

Ron

 

[MikeMl]

Your alternator/voltage regulator/battery keeps the car's system voltage at 14.2V +-0.2V when the engine is running. Why screw around with a secondary voltage regulator?

The proper way to run LEDs is in series; never in parallel! If your LED's max forward drop is 3.6V, wire three in series, then the current regulator can drop 14.2-3*3.6 = 3.2V. Make three sets of three, with one current regulator for each set.

 

[audioguru]

Haven't you seen instructables designed by people who know nothing about electronics and have a few LEDs in parallel?
One or two LEDs are very bright and the rest are dim. The bright ones have a lower forward voltage than the dim ones and hog the current. The bright ones with the low voltage and high current will burn out soon.
But LEDs in series all have exactly the same current regardless of their forward voltage.

If each "parallel" LED has its own series current-limiting resistor then there is a lot of wasted power in all the resistors but each LED can have any forward voltage.

Cheap Chinese flashlights have many LEDs in parallel but the LEDs are all tested and sorted so their forward voltages are all exactly the same. Maybe you can buy a few thousand LEDs and test them and sort them all. Then you can connect a few in parallel and they will all use the same current.

 

[bryan1]

Last year I bought a batch of 10 packs of 50 white led's for $5 each. They did say there could be 30% defunct, anyway out of each pack the best I found was 5-8 led's that were gone. In order to work out the forward voltage for each led all I did was use my fluke 865 on diode test to find each one. Surprisingly the group ended up in 4 groups using a 0.2 volt setting. To run them I used what a few resistors,a fet and a transistor and feed all of them off my free nife battery bank I got 7 years ago. Oneday I'll get a successful pic done of my shed in full led lighting. The shed is only 12x11 metres and although the led's aren't as bright as cfl lights they do provide a readable light in certain parts of the shed.

I will see if I can find the circuit as it has worked for me with those cheap led's now for over 5 years.

Cheers Bryan

Edit found the circuit


https://www.electro-tech-online.com/members/bryan1-albums-pic+dump-picture47511-led-cct-4.html