Advice 1: How to determine led current

LEDs are widely used in modern electronic equipment. Among their advantages are small size and bright light. But in order to make the led work properly, you need to correctly set its operating current.
How to determine led current
You will need
  • tester (multimeter);
Instruction
1
LEDs can serve for many years, one quickly fail if you are working at high current. To correctly calculate the amperage you need to know the voltage, which are designed for a specific led.
2
Voltage of most LEDs can be identified by the color of their glow. So, for white, blue and green led supply voltage is usually 3 V (valid up to 3.5 In). Red and yellow LEDs are on power supply voltage 2 (1,8 – 2,4 In). Most ordinary LEDs are rated at 20 mA, although there are LEDs in which the current can exceed 150 mA.
3
To estimate the rated current of the unknown led in the absence of reference materials is difficult. Look at the bulb - the bigger it is, the higher is usually the rated current. One of the signs that the prescribed current is higher than acceptable, can be a change in the spectrum of emitted light. For example, if the emission of the white led becomes blue, the current is clearly exceeded.
4
Don't forget that LEDs are very sensitive to excess voltage. For example, including led, designed for 2, in a circuit with two series-connected a 1.5-volt batteries (total 3 V), you can burn it.
5
If you use a supply voltage higher than recommended, the extra volts you need to pay additional (damping) resistor. Calculate resistance of resistor by the formula R=U/I. for Example, you need to power the led at 3 V on-Board vehicle network 12 V. you Have the extra 9 V. At a nominal led current of 20mA (0,02 A) you have the right value, dividing 9 by 0.02 – it will be 450 Ohms.
6
Gathering a scheme with led, be sure to measure the current consumed by it, to include the tester in the open circuit. If the current exceeds 20 mA, it should be reduced by increasing the value of the resistor. A little less talk – for example, 18 mA, just go led on the favor, increasing its service life.
7
Follow the correct connection of the led. To positive of power supply connected anode to minus and cathode. The cathode has a shorter output on the bulb with his hand made the cut (flat platform).

Advice 2: How to connect the led to the battery

Simplest led flashlight consists of led, resistor and battery. In some cases, is not required and a resistor. Such a lamp is less effective than more complicated, equipped with a transducer, but low price and speed of Assembly pay for this deficiency.
How to connect the led to the battery
Instruction
1
Find the voltage drop across an led depending on its colour according to the following table:- red: 1.9 In;
- yellow or green - 2.1 V;
blue or white - 3-4 V.
2
If you do not know the color of the led, briefly connect it to the lithium battery size 2016, 2025 or 2032. At the same time you will learn the polarity of the conclusions of the led, trying to connect it both ways. The element marking is applied on the positive electrode with a larger size. LEDs having a body (that is not implemented in the SMD version), this battery can be connected without any resistor. In any case do not short circuit the element.
3
If LEDs having a body, you are going to use a lithium cell, size 2016, 2025 or 2032 or three series-connected miniature zinc-manganese cells, size LR41 (L736, AG3), the resistor can not be used. To power from the same power sources SMD-diode it is recommended that a resistor of about 30 Ohms. When using three elements of the brand AG13 (LR44) is the same resistor will have to deliver consistently and with a corps led.
4
Sometimes the lights of industrial production to power blue or white LEDs include sequentially two 2016 batteries without a resistor. To do so is impossible, because it will lead to a rapid deterioration of the diode and the discharge element.
5
When you connect the LEDs to the power source, consisting of batteries of size AA or AAA, resistor use mandatory. If the led is red, yellow or green, you will need two cells in series, if the blue or white three.
6
The resistor initially take a resistance of 100 Ohms. Measure the current through the diode, and if it is more nominal, increase the resistance, if less, decrease. For diodes, rated current of which is unknown, choose it equal to 10 mA (for lighting LEDs with a diameter of 3 mm), 20 mA (for lighting larger diameter) and 3 mA (for SMD or any indicator).
7
Then measure the voltage drop across the resistor, multiply it by the current consumption, and get released on it power. If necessary, increase the nominal power of the resistor, pre-rounding it to the nearest value of the standard series.
8
Be sure to equip the lamp with a switch, adding it in series.
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