LED Lighting - 4th version


How often happened that you or someone in your family, by mistake, to overthrow the desk lamp? If you are like me, maybe this has happened many times...
If when I had installed in the desk lamp an incandescent bulb which costs 30 cents, the event was just unpleasant, now when I have a CFL bulb which costs over 6 USD, the event is "expensive". For this reason, the last time my offspring slammed my desk lamp with an innocent "UUPS!", I exclaimed Enough!


I decided that I have to replace the classic bulb or CFL from the desk lamp, with something more shock resistant...

But that could withstand the treatment of a 10 years child and at the same time to make enough light to work at desk in good condition, to be reliable in operation and decently priced? If only a few years ago, there was no a solution to this question, the answer is now clear: a power LED. As I already had some Cree MX6 Q5 LEDs with 3W power and maximum light output of 278 lumens used in LED Lighting - first version I decided to use them for this project too.


If the LED selection was the simplest part, powering him will be much more complicated ... or maybe not :)

For simplicity, I decided to use a switching power supply of a mobile phone, perhaps together with an electronic adapter that would give me the necessary voltage and current to power the LED.

For this purpose I have chosen the power supply of a defective mobile phone Siemens A52 having, according to the manufacturer, an output voltage of 5V and a current of 420mA.

According to manufacturer specifications, MX6 Cree Q5 LED can be powered at maximum current of 1A at a voltage of 4.1V, and I expected I'll need a 1 ohm resistor to lower the voltage by about 1V from the 5V (given by the power supply) to the 4.1V accepted by the LED, and that only if the power supply would handle the maximum current of 1A.

To check the maximum current supported by the power supply I connected to his terminals various resistors, measuring in each case the voltage and then calculating the current. Here are the obtained values:

Load Voltage Current
-NA- 5.8V 0A
8.2 ohm 4.9V 0.6A
5.1 ohm 3.1V 0.6A
3.3 ohm 1.75V 0.53A

EVRIKA!