Constant Current Source Circuit For Led

Constant current circuit using led.

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. U led u be r. And since the temperature coefficient of transistor and led fully offset. Or to put in another way.

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. Each led has a slightly differing voltage drop which is normal and why we want to use a ccs. In this case current is 1 25 4 7 266ma. Thus temperature occurs it does not affect the current flowing yet.

It s more consistent more efficient and more flexible. 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 term led power supply actually describes a constant voltage source and is used here rather colloquially. 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.

This controls the leds integrated in the lamp. An led driver is an electronic circuit that generates a constant output current from the supply voltage. 1 we use a lm317 in its constant current mode. From in the figure current i flowing through the value.

This is a very simple led constant current design using only 2 transistors 2 resistors and an led. We use also a 7805 regulator to build a constant current circuit. Its also known as led driver because many leds need 20 ma to light up. In electrical engineering this circuit is often referred to as a constant current source.

This is better than using a resistor.