My son is very interested in the LED. He wants to create the simple LED flasher circuit. But we should learn the principles of the LED before. There are many LEDs to use in the electronics circuits.
The LED is a light emitting diode. It is an electronic component that more complex than a lamp or an incandescent bulb. The LEDs have many colors to use. The important, they use a very small current,10mA.
There are many types of LEDs in the general Electronic stores. But now I like to use a standard LED 3mm and 5 mm in diameter in my electronic circuits projects. Because they are so cheap.
Pinout of the LED
This image is close up of 3 mm LED and is its pinout. It has the polarity like a diode. So, we must connect it in the right way or forward biased. It will not light up if connecting is wrong or reverse biased.
When we found a close-up of an LED. Firstly, the longer lead is positive(+) or anode(A). The other lead is shorter, is negative(-) or a cathode(K).
But sometimes it is the same lead. We need to look at a flat side on the LED. It always indicates the cathode(K) or negative(-). So the other is positive(+) or anode(A).
Then, look at the symbol of LED compared with a normal diode.
Why use symbols? If you draw the circuit, if the actual shape, it wastes so much time, symbols should be used.
It looks similar to the diode. The bigger triangle arrow will point the direction of flowing current. The smaller arrows on the diagram tell the emitting light.
The general, it does not show “+” or “-” on a diagram. It only shows the letter “K” to tell the cathode and A for the anode.
And, we often use the LED with a limiting current resistor.
Note: I think we do not need to understand the structure of the LED. At our level, just needing to use is enough.
How to test LED
To begin with, how much voltage does LED use?
Parts you will need
- A 3 mm red LED
- A power supply
- Voltmeter in a multimeter
My son gets a 3 mm red LED on the breadboard. Because it does not require an electric soldering iron. Perfect for him.
Then, he tries to use the adjustable DC power supply,1.25V to 25V 1A. To power to the LED. Caution! To start with 1.25V only.
- Now, The LED goes out.
- Then, adjust the voltage up to 1.5V. But LED still goes out(no light).
- The LED glows up when the voltage is 1.7V.
- When he adds voltage up to 2.2V it is too much hot.
- At 1.8V, LEDs are Best lighting and normal temperature
The LED voltage
In normally, all LEDs require current via resistor about 10mA for a small size(3mm), and 20mA for 5mm. But each of its colors requires a different voltage.
- Red LED: 1.7V
- Green LED: 2.3V
- Yellow LED: 2.3V
- Orange LED: 2.1V
- Blue LED: 3.3V
- White LED: 3.6V
This is a good character voltage drop. Because it is a constant voltage.
In the block diagram below. I will show you how to use the LED with 3V battery via the limiting current resistor in four colors, Red, Green, Yellow, and Orange. They use different resistance.
Note: Here is how to find the limiting current resistor.
Why LED does not glow?
If you connect the LED in a circuit. But it does not work. Why it does not glow?
For example the two circuits below.
- First, the red LED is connected in a reverse biased or wrong way.
- Second, the white LED requires 3.6V of a power supply. But now it has 3 battery only.
How to use a white LED
We add other one 1.5V battery to a circuit. Now we have a 4.5V battery. So we can use them to the white and blue LEDs.
This is just a basic how of using LED. When you make real projects. It may be good ideas for you.
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