10 Watt LED and LED Driver related question

Question

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.

Answer 1

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.

^{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.

Answer 2

I actually built myself a small lamp from one of these 10W "12V" datasheetless LEDs like this:

• buy half a dozen 1W 0.5ohm resistors
• bolt LED to aluminium heatsink (this is essential)
• put LED in series with resistors and power supply
• remove resistors until measured power in LED is about 9W (not 10W: derating it improves life and I don't trust the manufacturer)

(If the LED is the type built on an aluminium PCB, it will be a tremendous hassle to solder to it...)

Answer 3

You are going to have to measure, at the very least, the forward voltage of the LED when driven with perhaps 100mA.

When you know the approximate forward voltage, you can then calculate the required current. From those characteristics, you can either build or purchase a suitable power supply / driver circuit.

You know that the rated power is 10 Watts. The rest is easy, once you know the forward voltage of the LED.

Answer 4

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?

If you want to utilize the POWER LED to full potential then you should measure the thermal response of the LED in Current-Time domain. And it is related to your second question:

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?

Production of LEDs(particularly POWER LEDs) has some scattering within the process so the their Typical forward voltages are spreading between a voltage level(9 - 12 V in your case). When dealing with 10W power LED, you should aim a test method based on constant current rather than constant voltage. You can have the LED tested with this simple configuration:

^{simulate this circuit – Schematic created using CircuitLab}

Start From drawing 100 mA and go up to 2-3 A. See the forward voltage for a wide current sink. Then draw 0.5 A and check the temperature of the LED after a few hours. And then, you will have a countable data about your LED. If for 0.5A your LED does not produce Heat much, draw more current and repeat the test. Then you have a reliable data on your hand.