But instead of one LED, it has 15 LEDS, and the Vcc is 5V, but the circuit is basically the same. I'll guide through my process of calculating the dc bias resistors: First i pick the transistor, for the first time i chose BC337, i took a look at it's datasheet and followed the same process i did last time when i was passing 100mA through it's collector and emitter from a last project. I first choose the typ value of LED forward voltage, 3.2v, so after the LED, 1.8v remains to be used, then i say that collector voltage will be 1v, so it's a 0.8 drop to there, applying ohm's law:

0.8 = R * 0.02

R = 40

Then after that i check the gate current that i need to pass 300mA(15 LEDS), using this datasheet:

http://pdf.datasheetcatalog.com/datasheet2/3/06i96k727i3oloo2gis1ozg0jlyy.pdf

The gate current is about 2.1mA when Vce is 1.0v, so i make the gate voltage about 0.7v, so that the drop from base to emitter can happen and still maintain a Vce of 1.0v. Using ohm's law: 4.3 = R * 0.0021 ; R = 2047

And the emitter is tied at 0v, so it doesn't need resistors.

Then i plug these values into PROTEUS 8.3 and simulate it, and got a perfect result with the BC337AP model of bc337, so i went to test it and for my surprise the maximum collector current that i managed to achieve with this values was 180mA, giving 12mA for each LED. That was really a surprise, because i used this method 3 times, in three different projects and it worked everytime, it maaaay be a really nice coincidence of values, but i want to know where is my mistake.

I thought at first that was my transistor, so i went and bought BC638, TIP31C and a mosfet IRF822. I tested with TIP31C using the same method and i got the same result. One thing that is also surprising, is that in PROTEUS there is a BC337 model that is different from the BC337AP and this model is working more closely with my results, but it's still different. Can anyone point my errors ? Thanks in advance.