Constant Current Source Circuit For Led

The value of r3 divided into 1 25 volts will determine load current through each led in the string.

Constant current source circuit for led.

The input of the constant current source can be between 5v and 15v dc what is realy usefull for variable voltage sources. This is a very simple led constant current design using only 2 transistors 2 resistors and an led. And since the temperature coefficient of transistor and led fully offset. This controls the leds integrated in the lamp.

U led u be r. The t2 transistor can be bc547 if you use only usual leds the 20ma versions but it is recommended to use bd135 bd137 or bd139 because they have a higher power dissipation. The circuit is a constant current source which means that it keeps the led brightness constant no matter what power supply you use or surrounding environmental conditions you subject the led s to. From in the figure current i flowing through the value.

Its also known as led driver because many leds need 20 ma to light up. 1 we use a lm317 in its constant current mode. In this case current is 1 25 4 7 266ma. Thus temperature occurs it does not affect the current flowing yet.

Or to put in another way. This is better than using a resistor. An led driver is an electronic circuit that generates a constant output current from the supply voltage. The unloaded output will be the same voltage as the input 0 7v for the circuid it will regulate itself when you burden it.

3 7805 current constant circuit. We use also a 7805 regulator to build a constant current circuit. Each led has a slightly differing voltage drop which is normal and why we want to use a ccs. This circuit allows you to use any voltage between 2v and 24v to drive almost any type of led with power consumption up to 5w.

It s more consistent more efficient and more flexible.