LEDs are widely used in modern electronic equipment. Among their undoubted advantages are their small size and bright glow. But in order for the LED to work properly, it is necessary to correctly set its operating current.
Necessary
tester (multimeter)
Instructions
Step 1
LEDs can work properly for many years, one of them quickly fail if they work at increased current strength. To correctly calculate the current strength, you need to know the voltage for which a particular LED is designed.
Step 2
The supply voltage of most LEDs can be determined by the color of their light. So, for white, blue and green LEDs, the supply voltage is usually 3 V (up to 3.5 V is acceptable). The red and yellow LEDs are designed for a supply voltage of 2 V (1, 8 - 2, 4 V). Most conventional LEDs are rated for 20mA, although there are LEDs that can exceed 150mA.
Step 3
It is rather difficult to estimate the nominal current of an unknown LED in the absence of reference materials. Look at the bulb - the larger it is, the higher the normally rated current. One of the signs that the set current is higher than the allowable current may be a change in the spectrum of the emitted light. For example, if the emission of a white LED turns blue, then the current strength is clearly exceeded.
Step 4
Remember that LEDs are very sensitive to overvoltage. For example, plugging a 2V LED into a circuit with two 1.5V batteries in series (3V total) can burn it.
Step 5
If a supply voltage higher than the recommended one is used, the excess volts must be extinguished with an additional (damping) resistor. You can calculate the resistance of the resistor using the formula R = U / I. For example, you need to power a 3 V LED from the vehicle's 12 V on-board network. You have an extra 9 V. With a rated LED current of 20 mA (0.02 A), you will get the desired value by dividing 9 by 0.02 - this will be 450 Ohm.
Step 6
Having assembled the circuit with the LED, be sure to measure the current consumed by it by connecting the tester to the open circuit. If the current exceeds 20 mA, it must be reduced by increasing the resistor value. A slightly lower current - for example, 18 mA, will only benefit the LED, increasing its lifespan.
Step 7
Make sure the LED is connected correctly. The anode is connected to the plus of the power supply, the cathode is connected to the minus. The cathode has a shorter lead; a cut is made on the side of the flask (flat area).
