LED's

[WildCard6909]

How many LED's can be ran in series or parallel? How much power or volts would be required to run 60 LED's at once? Is there a way to run all 60 at once or would they have to be split up into 3 or 4 groups? What kind of resistors would be required to make them all run at the same brightness? Could capacitors be used to run all 60 at once or would this just blow out the circuit? Would solid state relays be a good way to good or would they serve no purpose?

Moved to General Hardware
Anandtech Moderator
Gillbot

 

[Gillbot]

You can run as many as you want, assuming your circuit can handle it.

Google will find you a calculator for the resistor(s)
http://ourworld.compuserve.com...es/Bill_Bowden/led.htm

 

[Harvey]

The two specs you need are the voltage drop across each LED and the current required to light it to the brightness you want it to show.

Typical red, orange, amberm yellow and green LED's drop around 2.5 - 2.8 volts. Blue LED's are closer to 4 volts, each. Your power supply must provide voltage equal to the voltage drop across each LED times the number of LED's in the string plus the drop across the circuitry used to set the current in the string, which can be a resistor or more complex transistor circuit.

For example, if you have red LED's with a typical voltage drop and a 12 volt supply, you could string 4 LED's in series.

12 volts / 2.5 volts per LED = 4 LED's leaving 2 volts available for the current setting circuit.

If each of these LED's requires 5 mA (.005 A) for the brightness you want to show, you can calculate the resistor value by dividing the 2 volt drop across it by the current through it.

2 volts / .005 mA = 400 ohms.

There are limits to the ways you can do this. For example, LED's of different colors, or even different models of the same colored LED from the same manufacturer, may have different voltage drops or different efficiencies (light output / at a given current). This means, for even color and light output, you should use the same type of LED for each string.

If your power supply isn't regulated to provide constant voltage at any current load, you can make a simple current setting circuit from as few parts as a 50 cent transistor, two resistors and a diode. This circuit would give you constant light output over a wide range of supply voltage, as long as the total voltage doesn't exceed the ratings of the components.

See this article for more info about current sources.

 

[imported_wired247]

LEDs are by definition DIODES which by definition do not obey Ohm's Law of V=IR. Diodes exhibit non-linear "resistance."

A lot of people run them in series for makeshift projects or just stringing a few LEDs together, because LEDs are fairly forgiving as long as you are over the threshold (turn-on) voltage and below the "make stuff break" voltage.

But really the best way to do LEDs (especially large numbers of LEDs) is in parallel, with the proper amount of voltage behind them (parallel means the voltages will be the same for all of them). As Harvey mentioned they hardly take up any current, but you should just do your research to see how much current one LED takes up, and then multiply that number by 60. For volts, 3 or 4 volts is usually sufficient. They can usually take quite a few more volts than that without blowing up, but 12V is starting to get pretty high.

 

[pcgeek11]

As stated above parallel is the way to do it properly

 

[JackMDS]

WSelcome to AnandTech forums.

WildCard6909 As you see there are many solutions/iterations to such question, if you would state you functional goal it would be easy to give you a good answer.

 

[corkyg]

OK - this is all good info - but, . . . how do they array LEDs in commercial light bulbs such as floodlights with a dozen or more LEDs? BTW - they are very "green," but horribly expensive.

 

[mpilchfamily]

That all depends on the AC to DC converter used in the bulb. They are expensive because of the number of LEDs used as well as the electronic involved. In a flood light there are allot more then a dozen LEDs in them. The average reading lamp LED bulb may have 12 LEDs but the lager bulbs use more. Basically though it comes down to what the converter outputs voltage and amperage wise. I you assume its converting the 110VAC to 12VDC then you can have a max of 4 3V LEDs in series. Then depending on the max amperage it can handle will determine the number of Series strings you can wire together in parallel. But the bulbs use a series parallel curicut to wire the LEDs together.

 

[Modelworks]

While the LED can just connect to AC the majority use a driver and transformer designed for the purpose.
Luxeon makes the brightest LED I have ever seen and they have them in all color mixes. Even one that is pure white by mixing various color LED.
http://www.luxeonstar.com/


They also have the drivers needed for low voltage where you can run multiple LED off one driver with the ability to dim, strobe, etc.
http://www.luxeonstar.com/low-...-drivers-c-41_18_4.php