Electrical – 10 Watt LED and LED Driver related question

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I got a 10watt LED from Ebay but never thought that the driver and heat sinks are must-haves for this little master. When googled, I found several circuits of LED driver. But none of them are precisely a 'simple' circuit with takes 12v 0.5mA ~ 1.5A DC input and lit the LED to full brightness. So here are my questions folks:

  1. I got few 220V to 12v transformers (with 500mA, 1A, 2A current ratings). Can you please give me a simple circuit diagram (preferably with a linear regulator or NE555 or any other easy-to-find IC/Transistor) to lit the 10 watt LED?

  2. Just saw a video, where the maker claims, even though the forward voltage rating of the LED is 9-12v, it will burn itself if connected to 12v and furnished a meaningful explanation. Whereas, we has shown that the LED glows ok with a simple 9v NiMH battery. I knew these LEDs need 2-3AMP current at 12 volts. What's the real fact of voltage and current for these LEDs?

Many thanks in advance. Please help.

Best Answer

Yet another simple LED driver request and yet another application for the LM317 as constant current source to be a simple (if somewhat inefficient) LED driver, but, being in current source mode, at least a good one for LEDs.

schematic

simulate this circuit – Schematic created using CircuitLab

You can get brave and figure a value for the resistor, or you can sneak up on it with adding resistors in parallel as shown at an early stage, given you have sketchy parts.

1.25 volts is maintained between Adj and Out (the principle of the LM317's operation) - so each 10 ohm in parallel will add 125mA to the output in this configuration; or if you think the thing should take 900 ma, you could put together some combination that would get you close to 1.38 Ohms. Note that you'll burn over a watt in that resistor as well as the dissipation in the LM317 itself (which is best regarded as a "smart resistor" at least for power use.) Other driver toplogies can be more efficient - this one is mostly simple, and involves just a few components.

As commented above "2-3A at 12V" would be 24-36 watts. 10 watts at 12V would be 833 mA, 10 watts at 9V would be 1111 mA. It is important to note that LEDs are primarily current driven devices - that is, the current, and especially the maximum current, is what you need to control.

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