# Power supply for 5*10 watt SMD LED?

I am new to electronics, I want to connect 10 watt leds like below diagram. What power supply should I connect, and how to calculate the required power supply for any number of LED of any Watt.

LED Specifications:

List item

• Item Type:LED Light (10 Watt)
• Intensity: Typical 800~900 Lumen
• Voltage: 9 to 12 Volt
• Forward Current:1000mA
• Beam Angle(°):120°
• Average Life (hrs):Greater than 50000 HRS
• Color:White Color
• Temperature:Cool White(5500-7000K)

• Is there a ".pdf" data sheet for the LED you can link? – Andy aka Dec 24 '15 at 8:56
• No man, I bought these form a local seller, but I have mentioned the data I have with me. – Amitabh Sarkar Dec 24 '15 at 9:17
• No datasheet = no good. A forward voltage range of 9V to 12V is either nonsense, or the LEDs are a load of crap or they are quoting a blue-sky 0mA to 1000mA Vf range, in all cases, you do not know, neither do we, no answer to be given. Buy an equally cheap constant current supply and hope things don't catch fire. – Asmyldof Dec 24 '15 at 9:20
• Maybe they have resistors built in to do current limiting. Maybe they have a little regulator? Who knows - don't buy any electrical components you've never used before unless you are sure you can get a data sheet (golden rule). Try them out - I can't advise. – Andy aka Dec 24 '15 at 9:26
• Ok @Asmyldof I agree with you, if we assume that forward v=12V and Forward current is 1000mA. Now is it possible to get the answer or some more things is needed? – Amitabh Sarkar Dec 24 '15 at 10:53

Here's a way of learning about the LEDs and improving your electronics knowledge.

LEDs are diodes and they exhibit a non-linear relationship between the voltage applied to them and the current through them. See the graph below. What this means is that as the voltage increases the current increase exponentially and we are in danger of smoking the LEDs.

To get around this problem we limit the current through the LEDs either with a resistor or a constant current power supply. Either way the current is limited to a safe value.

The next problem to address is that if the LEDs are paralleled as in your diagram uneven current distribution will occur. Due to manufacturing variation some will pass more current at a given voltage (and they all share the same voltage in your circuit). The one that's passing most current will heat up more than the other, allowing even more current through it, etc., until it fails. The pattern will repeat and you may blow all the LEDs.

If you wish to pursue this the best thing would be to get your hands on a bench power supply - borrow or go somewhere where you can use one for an hour and proceed as follows:

• Solder wires to the lugs of the LED.
• Mount the LED on a heatsink. 10 W is huge power for such a small die and you need to carry the heat away. You'll need thermal paste.
• Set the power supply voltage to 12 V. Set the current to zero.
• Connect the LED observing polarity.
• Switch on the power supply output. The voltage should drop to zero since you have set a zero current.
• Turn up the current slowly. You should get plenty of light by 100 mA and the voltage should have risen. Make a note of V and I.
• Repeat in 100 mA steps up to 1000 mA checking your heatsink temperature.
• If you have time, repeat the procedure for one or two more of the LEDs.
• Draw a graph and post it here (as an update to your original question).

You should get help then.

LED tutorial

• I liked your answer this explains a lot, But I cant get my handson this device. If we assume that forward v=12V and Forward current is 1000mA. Now is it possible to get the answer or some more things are needed? – Amitabh Sarkar Dec 24 '15 at 10:56

The lamp appears to have 9 LEDs in it, and white LEDs generally have a forward voltage drop of about 3.5 volts, so it appears they've arranged the LEDs as 3 paralleled strings of 3 LEDs connected in series, which would account for the 9-12 volt range in forward voltage.

If they're rated for a forward current of 1 ampere, then the best thing to do would be to connect the 5 lamps in series and drive them with a 1 ampere constant current source with a compliance greater than 60 volts, like this:

That'll allow the voltage drop across each lamp to become unimportant since the supply will only allow 1 ampere through the lamps.

One caveat is that if one (or more) of the lamps has a forward voltage of 12 volts and there's 1 ampere through it, it'll be dissipating 12 watts, not 10, so to stay within the 10 watt limit your power supply should be adjusted to 830 milliamperes.

Most important: You'll need to provide some heavy-duty heatsinking for the lamps.