Run a string of LEDs from the mains

[Ioannis]

How do i run the LEDs at 30mA instead of 50mA. Im lead to believe that if i use, for example, 5 LEDs on 12V instead of 4 then obviously the voltage drops but the current is supposed to drop too.

1. How do you run at 50mA ? The same way at 30mA.

2. What do you mean the voltage drops? Every LED needs a forward voltage of about 3.4 volts and the current should stay about 30mA. So if your source is 12 Volts then your resistor which should always considered there has to drop the rest of thevoltage that is 12-3.4=8.6 and its vaue would be 8.6/.03=286.6 ohms

Now if you want in series more leds, thats OK. put up to 3, and 3 x 3.4 = 10.2 volts. The rest should be dropped on the resistor in series. You cannot omit the resistor and put another LED. Chances are that they will not light.

Why? The answer is simple. Look at the characteristic curve of a diode (or LED, its the same). It conducts the forward voltage at a very specific point and increasing the voltage slightly, the current increases dramaticaly. I said that on my previous post but you did not give it attention.

Look at the attached photo.

Ioannis