LED light circuit design (high power)

1. LED light circuit design (high power)

Hello every body,
I'm making LED lights (120 Watts) by using LED 1 watt.
I wonder if you answer me these questions?

Do LED lights circuit require current limiting circuit?
What ways do you suggest for designing LED lights circuit?(What is the best number of LED in series and parallel?)

Could you Please recommend resources about this subject?
tanx

2. Re: LED light circuit design (high power)

LED's definitely require current limiting - you need to use a controlled current supply.

You can wire as many LED's in series as you want/can supply voltage for (each LED forward voltage, added up) / can supply safely with enough voltage (don't want people being fried with 400 volts!). If one LED wants 500mA at 4V, then ten in series will need 500mA at 40V.

Don't wire LED's in parallel without serious thought. Each one will vary slightly in the forward voltage with a given current - the effect being that they will share current unequally. That can cause the harder-driven one to eventually overheat (as the LED warms up, its forward voltage drops, get more current, gets hotter...) You might get away with it, or you might not. With a lot of expensive LED's, I would not risk it. Drive each series LED string with its own regulated current, or use a current mirror. See here: http://www.ledsmagazine.com/features/6/2/2

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3. Re: LED light circuit design (high power)

Agree w/ FoxyRick on not connecting LEDs in parallel (directly). The simplest method to wire up lots of LEDs is to build multiple "modules". Each module consists of several LEDs, in series with a current-controlling element (series resistor or constant-current control circuit). Then you can connect multiple "modules" in parallel at your voltage source to get the overall quantity of LEDs you need.

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4. Re: LED light circuit design (high power)

thank you because of mentioning important points.

I want to make a 120W LED street light.I searched several ICs that are suitable for this purpose (LM3402HV).
let me know, is there any other way to make a 120W LED street light with below properties?
* low power dissipation (high efficiency)
*current limiter

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5. Re: LED light circuit design (high power)

What is the LED light product's input voltage?
Which circuit topology do you use?

6. Re: LED light circuit design (high power)

I think it's better to use 48VDC as power supply.
according to my searches ,buck topology is the best topology.
see attached file

7. Re: LED light circuit design (high power)

Hello again

I have several question.I was wondering if you help me.
1) Has a 84 watt led light enough brightness(to compare with 250W halogen) ?
2) Is it practical to use a transformer(220v to 110v) and rectifier then use TL783 and drive 14 LED in series?(see attach) [do you have another idea?]
Thank you

8. Re: LED light circuit design (high power)

i slao want to make a 120w led aquarium lights

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9. Re: LED light circuit design (high power)

1W led typically has VF about 3.5-4V and current of 350mA. To get 120W you need to wire let's say 20 series connections of 6 leds each (or 10 time 12 each). So you need 10 current sources that can provide 300-350mA about 50V. This is not very cheap circuit, especially multiplied times 10. Additionally you have to provide decent heatsinking, because 120W worth of powerleds will produce MASSIVE amounts of heat.

I've made some experiments with 3 leds on aluminum core pcb glued with thermodonductive paste to PC motherboard chipset heatsink (square ~40x40mm). At 250mA I couldn't touch it after about 10 minutes and surface temperature was above 60*C. Multiply that by 40 and you'll get a feeling how much heat you have to disperse at such power and what size of heatsink you'll have to use.

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