Led constant current driver lm317

This IC is primarily intended as an adjustable voltage regulator, but can easily be adapted for use in regulating current. The LM is very easy to use in a constant current mode. It will always strive to keep its output voltage at exactly 1. It has an I f forward current of mA and a V f forward voltage of 3. The formula for calculating the right value for R for use with the LM is:. A half-watt resistor will, therefore, be fine.

The LM also needs its input to be about 3V higher than its output to guarantee 1. This means that a 6V battery would not be quite high enough because the forward voltage is 3. However, we could drive the circuit using a 9V battery or even a 12V power supply without modification, since whatever the input voltage, the current will always be limited to about mA.

A quick calculation of the power consumed by the LM will reassure us that we are not going to come near exceeding its maximum power rating. For a 9V battery, the voltage between In and Out will be. The current is mA, so the power is:. According to its datasheet, the maximum power handling capability of the LM is 20W, and it can cope with a current of up to 2. So we are fine.

The automatic light controller offers energy saving and convenience in the areas with a photosensor…. When using an LM regulator, less wattage will be lost in the resistor and more heat will be generated via the regulator, when compared with a a however the total wattage lost will b the same in both cases. Driving a single 1watt LED from 12v is very inefficient. The voltage across the LED will be about 3. The remaining 8. The 4R2 must have 1. The minimum voltage across a LM is about 3v and this voltage is required to operate the circuitry inside the regulator.

This means two 1watt LEDs can be placed on a 12v supply and the regulator will run cooler while the circuit will produce twice the light-output for no additional current.

More on LED drivers on my next post. This site uses Akismet to reduce spam. Learn how your comment data is processed. Here I'll concentrate on the use of a constant current source for lighting light emitting diodes or LEDs. Understanding series circuits and voltage drops will help with this subject.

Briefly in a series circuit the current through all series components is the same, while the sum of the voltage drops across each series component will add back to the source voltage. In Fig. The value of R3 divided into 1.