Power regulator board to connect to 7 CREE LEDs? / LED flashing board?

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Nitrixflare

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Okay information first:
CREE green LEDs,
3W each, 4.5V
I'm going to run seven of them using 3 D-sized 1.5v batteries so it's direct current. I've heard of circuit boards designed to work as power regulators to prevent them from sucking up the power from the batteries too fast, but these boards are usually designed for normal or superbright LEDs, not CREE. Also these boards usually can only handle about 3 or 4 LEDs, but I need to wire 7 of them. Can anyone provide a schematic with parts list for a more "heavy-duty" version of the power regulator board? Or does anyone have a link to a webpage with more information on that "heavy-duty" model?

Next I need a circuit board that allows LEDs to flash. Same thing again, some of these boards do not accept up to 7 LEDs. Also due to the LEDs being CREE I worry if the normal boards can operate them. A little advice please?

Thanks!
Nitrixflare
 
First advice is that LEDs need a resistor to limit their current. You can't get them to work by starting with the same voltage they need and just letting them take what they need...unless CREE LEDs are designed with their own resistors. The schematic for a resistor is very simple. I think you can do that for your self. For instance, 4 batteries, 1.5 volts extra, 2/3 of an amp, 2.25 ohms. Buy 2.2 ohms, 2 watts.

as for the rest of your request, you can usually get some help on this site, but getting somebody to just design the whole thing for you is not likely to get results.
 

Thats a good way to either disappoint him or destroy his expensive LEDs
 
Adding current limiting resistors destroys LED's?
Apparently I have a lot to learn.
 

An LED is an LED, being from CREE does not make a difference. Also this sounds a lot like a flashlight sort of thing... not going to happen... you need to get the heat away from the LEDs and with 7 of them that is a MAJOR thermal issue.

https://www.electro-tech-online.com/custompdfs/2010/07/D_Ind_Bat_Data_Sheet.pdf you are talking about a 6A drain on batteries that might last 1 hour at 2A. At 6A you will be lucky to get 10 minutes out of them and that is assuming you are only losing 20% in your driver circuit.

Dan
 
I think by CREE he means the high power (3W) type of LEDs, rather than the 20mA version. his just happen to be from CREE.

dont think its possible to run 7 x 3W leds from D cells, unless you are limiting the current to them, essentially making them... not high power LEDs any more. You should be expecting to pull 4.66A for JUST the LEDs

furthermore, each LED needs 4.5V, but that doesnt mean your supply voltage can be 4.5V (which i assume is how you got to 3 D-cell batteries - 3 x 1.5V = 4.5V). The voltage will sag after a little while, and you will need a little overhead voltage for a current limiting circuit. 4 D cells in series would be a minimum, but, as Ubergeek already said, it only last 10 minutes at best.
 
I haven't looked at Cree but most other high power LED manufacturers recommend using a constant current source circuit instead of resistors to regulate the current instead of simply limiting the current which is not safe. The reason is that each LED has a different forward voltage (I guess 4.5V is the typical voltage) that could be 4.2V then with a resistor the current will be too high and could be 4.8V then the current will be too low. The constant current source needs some additional voltage to keeep working then it holds the current (and brightness) constant as the battery voltage runs down.
 
Dx3 said:
Adding current limiting resistors destroys LED's?
Apparently I have a lot to learn.
Click to expand...

adding insufficient current limiting to LEDs with an unstable voltage does ... though it is not the current limit it is the varying voltage that kills them.

Think about it, 3 LEDs in series in a car a "12V" system. (12V-3.5V*3)/1A=1.5 ohms ... then the alternator starts up to charge the battery ... (14V-3.5V*3)/1.5 ohms = 2.3A

your problem on dry cells would be the opposite, assuming you had enough capacity to bother: (1.5V*3-3.5V)/1A=1 ohm but at end of life you get (0.9*3-3.5)/1 ohm ... well that is a negative number so you get zero... the only saving grace is that the LEDs voltage goes down as you drop the current as well so it might light still .... a little.

Dan
 
A manufactured LED does not have a certain voltage, it has a range of voltages. The manufacturer states the "typical" voltage that could be much lower or much higher for each LED. You could use a resistor to limit the current if you measure the actual voltage of each LED then calculate the resistor value but you also must keep the LED cool somehow because its voltage and resulting current changes when its temperature changes.

A resistor for current-limiting allows the LED to dim as the battery voltage runs down. The current might be too high and burn out the LED when the battery is brand new.
A contant current source has none of these problems.
 
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