# Circuit of Lighting LED

[Key words]

・What is the LED

・Relationship with Voltage and Color of LED

The first posted on the “Blead board Circuit library” that “L-tika” is the first step in Electronics Work.　LEDs are used in all kinds of products that Light, such as about LED display. light bulbs and TV.　So, what should we do to make the LED lighting? Actually. It is not doing that connect the LED directly to the Battery.　In this article, I will explain how to use such LEDs from the basics. Let’s get started.

## ・What is the LED

So what are the characteristics of LED. LED means about “Light Emmiting Diode” It’s
can be made to Light by passing a current. Fig1 is schematic symbol. Down triangle and one horizontal bar, it is a symbol of diode. And two arrows outward. It is LED symbol.
Photo 2 shows the appearance of the LED. The LED is cylindrical and has a dome-shaped tip. The LED has two terminals, named anode (A) and cathode (K), respectively. It’s the same as a diode. Current can only flow from the anode to the cathode. Therefore, the voltage is made to shine by connecting a plus to the anode side and a minus to the cathode side and applying a voltage. However, if it glows when voltage is applied, everything can be solved by connecting a battery. Is not. In reality. You have to connect the current limiting resistor, which will be explained later. It is generally said that the longer lead wire is the anode and the shorter lead wire is the cathode. However, in that judgment, you will not know when you cut the lead wire. Therefore, as another way of distinguishing, if you look closely inside the LED, as shown in Fig. 2, there are lines with an inverted triangular base and lines without it. This triangle is the base on which the LED chip (semiconductor) is placed, and this is mostly the cathode.

## Circuit of Light one LED

Now let’s turn on the LED.
Figure 3 shows the circuit that illuminates one LED. If you look closely, you can see that the resistor (R1) is connected in series in addition to the LED and the dry battery. This is called the current limiting resistor. It will be a little difficult story, so I will explain it briefly, but the current and voltage that can be passed through the LED are fixed. For red LED, it is 10mA 2.1V. Then, since the voltage of one dry battery is 1.5V, one dry battery is not enough, and two dry batteries (3V) are too high voltage. If the voltage is too high, a large amount of current will flow, so insert a resistor between them to adjust the voltage and current. See the column below for more details. The resistance to illuminate a 2V, 20mA LED with respect to a dry battery of 3V is about 51Ω. Please remember it roughly. Let’s actually make it. Fig. 4 is a wiring diagram for illuminating one LED. First of all, let’s wire this way. The direction of the LED is + for the anode and-for the cathode, so point the longer leg to the positive pole side of the battery (the one that connects to the resistor in Fig. 4). Also, there is no direction for resistance.

## Circuit of Light two LEDs

Next, let’s add an LED. Adding an LED is easy. Just increase the same circuit as it is as shown in Fig. 5 and Fig. 6. However, please note that the resistance should be increased by the number of LEDs. When multiple LEDs are attached with one resistor, the currents for the number of LEDs are added up first, so the loss on the resistor increases and heat is likely to be generated. Therefore, it is necessary to attach a large resistance. In addition, there are individual differences in LEDs, and even if the same type of LED is connected, if an LED that easily flows current and an LED that does not easily flow are connected, a lot of current will be taken away by the LED that easily flows, and the other will have good light and unstable operation. Will be. Therefore, let’s add resistance to each.

## Light any LEDs that kinds of color

Next, Let’s connecting LED other Red color.
Now,add the Blue and Yellow LEDs. As shown in Fig. 7 and Fig. 8, the voltage and current of each color LED and the resistance value in the case of 3V and 6V are shown.

Red　2.0V 20mA [3V]51Ω　[6V] 330Ω
Yellow　2.1V 20mA [3V]51Ω　[6V] 330Ω
Blue　3.1V 30mA [3V]No Light [6V]100Ω

I’ll show you the details in a column, but it’s a good idea to keep this in mind. Two batteries are not enough for the blue LED because it has to apply a voltage of 3.2V. Therefore, I moved it at 6V and connected a limiting resistor of 100Ω. Since the voltage to be dropped is lower than that of red and the current is large, the resistance value is small.

### Used parts

The parts used this time are shown below. Please challenge yourself.

The breadboard is not included in the parts list, so please procure it separately.

## Collum(Calculated about Resistance of LED)

Now, let’s talk a little difficult. Here’s how the LED current limiting resistance is calculated. First, the calculated value of the current limiting resistance can be calculated by the following formula.

The resistance R [Ω] is the voltage applied to the resistance, which is the value obtained by subtracting the LED voltage (listed in Vf in the data sheet) from the battery voltage VBAT according to Kirchhoff’s voltage law. For example, in the case of Fig. 9, the voltage applied to the resistor is 1V when the battery voltage is 3V and the LED voltage is 2V. In order to apply a voltage of 1V to this resistor and allow 20mA to flow through the LED, according to Ohm’s law, 1V ÷ 20mA is 50Ω. There is no 50Ω resistance on the market, so we use 51Ω, which has the closest resistance value on the market.