LEDs are everywhere – in our phones, in our cars, and even in our homes. Whenever an electronic device lights up, there is a good chance that an LED is behind it.

LEDs are like tiny lightbulbs. Low energy consumption, small size, rapid switching and long lifespan makes them ideal for mobile devices and other low-power applications.

LED stands for Light Emitting Diode. They are a special type of diode that convert electrical energy into light. They have very similar electrical characteristics to a normal PN junction diode. That’s why the symbol of LED is similar to the normal PN junction diode except that it contains arrows pointing away from the diode indicating that light is being emitted by the diode.

[!NOTE]

LED 无处不在——在我们的手机、汽车、甚至我们的家中。每当电子设备亮起时，很可能就有一个 LED。

LED 就像微型灯泡。低能耗、小尺寸、快速切换和长寿命使它们成为移动设备和其他低功耗应用的理想选择。

LED 即发光二极管。它们是一种将电能转化为光的特殊二极管。它们的电气特性与普通的 PN 结二极管非常相似。这就是为什么 LED 的符号与普通的 PN 结二极管相似，只是它多了朝向二极管外部的箭头，表示二极管正在发光。

LED Construction（LED 的结构）

LEDs are so common, they come in a huge variety of shapes, sizes and colors. The LEDs you are most likely to use are the standard through hole LEDs with two legs. Following figure shows the parts of it.

[!NOTE]

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LED 非常普遍，它们有各种各样的形状、尺寸和颜色。你使用的最多的可能是两个引脚的标准通孔 LED。如下图所示。

The construction of an LED is very different from an ordinary diode. The PN junction of an LED is surrounded by a transparent, rigid plastic epoxy resin shell.

The shell is constructed in such a way that photons of light emitted by the junction are focused upward through the domed top of the LED, which itself acts like a lens. This is why the emitted light appears brightest on top of the LED.

[!NOTE]

LED 的结构与普通二极管非常不同。LED 的 PN 结被透明的刚性塑料环氧树脂外壳包围。

外壳的构造使得 PN 结发射的光子通过 LED 的圆顶向上聚焦，而圆顶本身就像一个透镜，这就是为什么发射的光在 LED 顶部看起来最亮的原因。

Just as in an ordinary diode, the positive side of the LED is called the Anode, while the negative side of the LED is called the Cathode. The cathode is usually indicated by having a shorter lead than the anode. Not only this, the outside of the plastic case typically has a flat spot or notch which can also indicate the cathode side of the LED.

Not all LEDs are hemispherical in shape, some are rectangular while some are cylindrical, but they are mostly constructed in the same way.

[!NOTE]

就像普通二极管一样，LED 的正极称为阳极，而 LED 的负极称为阴极。阴极通常通过比阳极更短的引脚来表示。不仅如此，塑料外壳的外部通常有一个平坦的点或凹口，也可以表示 LED 的阴极侧。

并非所有 LED 都是半球形的，有些是矩形的，有些是圆柱形的，但它们的构造大多相同。

LED Working（LED 的工作原理）

Like an ordinary diode, the LED operates only in forward bias condition. When the LED is forward biased, the free electrons cross the PN junction and recombine with holes. Since these electrons fall from a higher to a lower energy level, they radiate energy in the form of photons (light).

In ordinary diodes, this energy is radiated as heat while in an LED, energy is radiated as light. This effect is called Electroluminescence.

[!NOTE]

与普通二极管一样，LED 仅在正向偏置条件下工作。当 LED 正向偏置时，自由电子穿过 PN 结并与空穴重新结合。由于这些电子从较高能级下降到较低能级，它们以光子（光）的形式辐射能量。

在普通二极管中，这种能量以热量的形式辐射，而在 LED 中，能量以光的形式辐射。这种效应称为电致发光。

LED Colors（LED 的颜色）

Light emitting diodes are available in a wide range of colors with the most common being red, green, yellow, blue, orange, white and infrared (invisible) light.

Unlike ordinary diodes that are made of germanium or silicon, LEDs are made of elements such as gallium, arsenic, and phosphorus. By mixing these elements together in different proportions, a manufacturer can produce LEDs that radiate different colors as shown in the table below.

[!NOTE]

发光二极管有多种颜色可供选择，最常见的是红光、绿光、黄光、蓝光、橙光、白光和红外光（不可见光）。

与由锗或硅制成的普通二极管不同，LED 由镓、砷和磷等元素制成。通过以不同的比例混合这些元素，制造商可以生产出发出不同颜色的 LED，如下表所示。

Color	Wavelength   (nm)	Forward Voltage (V)	Material
Ultraviolet	<400	3.1-4.4	Aluminium nitride (AlN) Aluminium gallium nitride (InxGa1-xN)
Violet	400-450	2.8-4.0	Indium gallium nitride (InxGa1-xN)
Blue	450-500	2.5-3.7	Indium gallium nitride (InGaN) Silicon carbide (SiC)
Green	500-570	1.9-4.0	Gallium phosphide (GaP) Aluminium gallium phosphide (ALGaP)
Yellow	570-590	2.1-2.2	Gallium arsenide phosphide (GaAsP) gallium phosphide (GaP)
Orange	590-610	2.0-2.1	Gallium arsenide phosphide (GaAsP) gallium phosphide (GaP)
Red	610-760	1.6-2.0	Aluminium gallium arsenide (AIGaAs) Gallium arsenide phosphide (GaAsP) Gallium phosphide (GaP)
Infrared	>760	>1.9	Gallium arsenide (GaAs) Aluminium gallium arsenide (AlGaAs)

[!NOTE]

颜色	波长   (nm)	正向电压 (V)	材质
紫外线	<400	3.1-4.4	氮化铝（AlN） 氮化铝镓（AlGaN）
紫色	400-450	2.8-4.0	氮化铟镓（InxGa1-xN）
蓝色	450-500	2.5-3.7	氮化铟镓（InxGa1-xN） 碳化硅（SiC）
绿色	500-570	1.9-4.0	磷化镓（GaP） 磷化铝镓（AlGaP）
黄色	570-590	2.1-2.2	磷砷化镓（GaAsP） 磷化镓（GaP）
橙色	590-610	2.0-2.1	磷砷化镓（GaAsP） 磷化镓（GaP）
红色	610-760	1.6-2.0	砷化镓铝（AlGaAs） 磷砷化镓（GaAsP） 磷化镓（GaP）
红外线	>760	>1.9	砷化镓铝（GaAs） 砷化镓铝（AlGaAs）

The actual color of an LED is determined by the wavelength of light emitted, which in turn is determined by the actual semiconductor material used to make the diode.

Therefore the color of the light emitted by an LED is NOT determined by the color of the body of the LED. It just enhances the light output and indicates its color when it is not illuminated.

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LED 的实际颜色由发射光的波长决定，而波长又由制造二极管所用的实际半导体材料决定。

因此，LED 发射光的颜色并非由 LED 主体的颜色决定。它只是增强了光输出，并在不发光时显示其颜色。

LED Voltage and Current（LED 的电压和电流）

For most low-power LEDs, the typical voltage drop is from 1.2V to 3.6V for currents between 10mA to 30mA. The exact voltage drop will of course depend upon the semiconductor material used, color, tolerance, along with other factors.

As the LED is basically a diode, its IV characteristics curves can be plotted for each color as shown below.

[!NOTE]

对于大多数低功率 LED，电流在 10mA 至 30mA 之间时，典型压降为 1.2V 至 3.6V。确切的电压取决于所使用的半导体材料、颜色、容差以及其他因素。

由于 LED 基本上是二极管，因此可以为每种颜色有其对应的伏安特性曲线，如下图所示。

[!NOTE]

Unless otherwise specified, you should consider a nominal drop of 2V and forward current 20mA.

除非另有说明，否则应考虑 2V 的标称压降和 20mA 的正向电流。

LED Brightness（LED 的亮度）

The brightness of an LED depends directly on how much current it draws. The more current it draws, the brighter the LED will be.

You can control the brightness of an LED by controlling the amount of current through it.

[!NOTE]

LED 的亮度直接取决于其消耗的电流量。消耗的电流越多，LED 就会越亮。

可以通过控制流过 LED 的电流来控制其亮度。

The Current Limiting resistor（限流电阻）

If you connect an LED directly to a battery or power supply it will try to dissipate as much power as possible, and, it will destroy itself almost instantly.

Therefore it is important to limit the amount of current flowing through the LED. For this, we use resistors. The resistor limits the flow of electrons in the circuit and prevents the LED from trying to draw too much current.

The current-limiting resistor is placed between LED and voltage source in this way:

[!NOTE]

如果将 LED 直接连接到电池或电源，它会试图消耗尽可能多的电量，并且几乎会立即烧毁。

因此，限制流过 LED 的电流非常重要。为此，我们使用电阻。该电阻限制电路中的电子流动，并防止 LED 试图吸取过多的电流。

限流电阻放置在 LED 和电压源之间，如下图：

In above circuit, the resistor has a node voltage of $V_S$ on the left and a node voltage of $V_F$ on the right, the voltage across the resistor is the difference between the two voltages.

By applying Ohm’s law, the current-limiting resistor is calculated as:

[!NOTE]

在上面的电路中，电阻左侧的电势为 $V_S$，右侧的电势为 $V_F$，电阻两端的电压为两个电势之差。

根据欧姆定律，限流电阻的计算公式为：

$$R_S=\frac{V_S-V_F}{I_F}$$

Basic Example（基本示例）

Consider a red LED with a forward voltage drop of 1.8V is connected to a 5V DC power supply. Calculate the value of the current-limiting resistor required to limit the forward current to approximately 10mA.

[!NOTE]

假设一个正向压降为 1.8V 的红色 LED 连接到 5V 直流电源。计算出正向电流约为 10mA 的限流电阻值。

Solution:（解决方案）

Using the formula above, the current-limiting resistor is:

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由上述公式可得限流电阻为：

$$\begin{gathered} R_S=\frac{V_S-V_F}{I_F} \\ =\frac{5V-1.8V}{10mA} \\ =\frac{3.2}{10\times 10^3}\Omega \\ =320\Omega \end{gathered}$$

This suggests that we will need a 320Ω resistor to limit the current to 10mA. But 320Ω is not a standard preferred value, so we will need to choose the next highest value, which is 330Ω.

Let’s recalculate the forward current for the 330Ω current-limiting resistor:

[!NOTE]

这表明我们需要一个 320Ω 电阻来将电流限制在 10mA。但 320Ω 不是标准的首选值，因此我们需要选择下一个最高值，即 330Ω。

让我们重新计算 330Ω 限流电阻的正向电流：

$$\begin{gathered} I_F=\frac{V_S-V_F}{R_S} \\ =\frac{5V-1.8V}{330\Omega } \\ =\frac{3.2}{330}A \\ =0.0096A \\ =9.6mA \end{gathered}$$

We got a new forward current value of 9.6mA which is fine.

[!NOTE]

我们得到了一个更好的正向电流值 9.6mA。

Multi-color LEDs（多彩 LED）

Most LEDs produce only one output of colored light. However, multi-color LEDs are now available that can produce a range of different colors from within a single device. These actually have several LEDs fabricated in a single package.

[!NOTE]

大多数 LED 只能输出一种颜色的光。但是，现在市面上有多色 LED，它们可以在单个设备中发出多种不同颜色的光。实际上，这些 LED 在单个封装中包含了多个 LED。

RGB LEDs（红绿蓝 LED¹）

At first glance, RGB (Red, Green, Blue) LEDs look just like regular LEDs, however, inside the usual LED package, there are actually three LEDs, one red, one green and yes, one blue. By controlling the intensity of each of the individual LEDs you can mix pretty much any color you want.

[!NOTE]

乍一看，RGB（红、绿、蓝）LED 看起来就像普通 LED，然而，在普通的 LED 封装结构内，实际上封装了三个 LED，一个红色，一个绿色，当然还有一个蓝色。通过控制每个 LED 的发光强度，几乎可以混合出任何颜色的光。

The RGB LED has four pins: one for each color, and a common pin. On some, the common pin is the anode, and on others, it’s the cathode.

[!NOTE]

RGB LED 有四个引脚：每个颜色一个，还有一个公共引脚。有些 LED 是共阳极，有些 LED 是共阴极。

Bi-Color LEDs（双色 LED）

Unlike RGB LED, Bi-color LED lacks blue LED inside the LED package. Typically, there are only two LEDs, one red and one green. By controlling the intensity of each of the individual LEDs you can mix only shades of Red and Green only.

[!NOTE]

与 RGB LED 不同，双色 LED 封装内没有蓝色 LED。通常，只有两个 LED，一个红色，一个绿色。通过控制每个 LED 的强度，只能混合红色和绿色的色调。

The Bi-color LED has three pins: one for each color, and a common pin. Similar to RGB LED, On some, the common pin is the anode, and on others, it’s the cathode.

[!NOTE]

双色 LED 有三个引脚：每种颜色一个，还有一个公共引脚。与 RGB LED 类似，有些 LED 是共阳极，有些 LED 是共阴极。

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1. 通常是不翻译的，因为 RGB LED 也是常用的口语词汇 ↩︎