First of all, if you want to use this LED light, you must know its characteristics. This is a data manual about red in-line 3mm light-emitting diodes found on the Internet. We can see from the voltage-current transmission characteristic curve of the manual that the cut-off voltage is 1.6V, and when it is less than 1.6V, the light-emitting diode does not conduct. . When the turn-on voltage is 1.8V, the current is 10mA, and then as the turn-on voltage increases, the current also increases proportionally.
We know its features just now, and we will start using it now. In our weak current system, the power supply is mostly 5V or 3.3V. Here we take the 5V power supply as an example. It can be seen from the above parameters that when the 5V power supply is directly applied to the two ends of the LED light, a large forward continuous current will be generated. We also know that when the forward continuous current exceeds 25mA, the LED light will be damaged. At this time, a resistor needs to be connected in series to limit the current and share a part of the current to the resistor to ensure that the LED lamp is used normally without damage. This resistor is the legendary "current limiting resistor", so what we really want to say today Circuit.
This is the most classic and commonly used LED lamp circuit.
So now the problem comes again. In the above circuit, the power supply is determined to be 5V, and the LED light is also determined. Then, how big should I choose the current limiting resistor? At this time, you need to determine the resistance value according to the two parameters mentioned above: IF and UF. The calculation is as follows:
The voltage across the resistor: 5V-2.1V≤UR≤5V-1.6V;
Resistance size: (5V-2.1V)/25mA≤R≤(5V-1.6V)/0.01mA;
You can get: 116Ω≤R≤340kΩ.
Therefore, the resistance here can be selected as long as the resistance is within this range. It just means that the smaller the resistance value, the larger the current flowing through, the brighter the LED light; the larger the resistance value, the smaller the current flowing through it, and the darker the LED light will be. Usually in practical applications, the LED lamp conduction voltage is 1.7V, and the forward continuous current is 10mA. From this parameter, the value of the current-limiting resistance can be simply obtained.
This is the application of LED lights in power indicator lights. If LED lights are used for board-level operation indicators, how should they be done? it's actually really easy.
Here we only need to give high and low levels on the Control side. When the high level is applied, the LED light does not turn on, and the LED light does not turn on at this time. After a period of time, when the low level is applied, the LED light turns on, and the LED light is on at this time. Repeat this operation, you can see the status of the LED light: on-off-on-off. . .
The flashing frequency of the LED light depends on the duration of the high level and low level.
LED lights are actually light-emitting diodes. Now what we see is the circuit symbol of LED, which is not the true face of it. Please look at the picture below, is it a lot taller in one go? The colors and shapes are different and varied. For so many LED lights, it is necessary to classify them at this time, otherwise the brain is too difficult to remember.
LED lights can be divided into:
Red, green, blue, yellow, white, etc.
LED lights can be divided into:
In-line,
In-line LED lights can be divided into cylindrical, flat, and special-shaped according to their shape.
Straight-insertion cylindrical LED lamps can be divided into straight-insertion 3mm and straight-insertion 5mm according to the diameter of their lamp beads.
Patch,
SMD packages are 0603, 0805, 1206, 2835, etc.
According to its turn-on voltage and turn-on current, LED can be divided into:
High-power LED lights (usually used for lighting) and low-power LED lights (usually used for power indicator lights or running indicators on circuit boards)
PARAMETERS
