什么是光电二极管？工作，V-I特征，应用程序

什么是光电二极管？

它是一种光传感器的形式，可将光能转换为电能（电压或电流）。Photodiode是一种具有PN连接的半导电设备。在P（正）和N（负）层之间，存在一个固有的层。照片二极管接受轻能作为产生电流的输入。

它也称为光电探测器，光传感器或光检测器。光电二极管在反向偏置条件下运行，即光电二极管的P - 侧与电池的负端子（或电源）和N - 侧与电池正端子连接。

典型的光电二极管材料是硅，锗，砷酰胺磷化物和砷化镁。

Internally, a photodiode has optical filters, built in lens and a surface area. When surface area of photodiode increases, it results in less response time. Few photo diodes will look like Light Emitting Diode (LED). It has two terminals as shown below. The smaller terminal acts as cathode and longer terminal acts as anode.

The symbol of the photodiode is similar to that of an LED but the arrows point inwards as opposed to outwards in the LED. The following image shows the symbol of a photodiode.

光电二极管的工作

通常，当发出照明PN连接点时，共价键将被电离。这会产生孔和电子对。由于电子孔对的产生而产生光电流。当能量超过1.1EV命中二极管时，会形成电子孔对。当光子进入二极管的耗竭区域时，它会以高能量击中原子。这导致电子从原子结构释放。电子释放后，会产生游离电子和孔。

In general, an electron will have a negative charge and holes will have a positive charge. The depletion energy will have built-inelectric field。由于电场，电子孔对远离了连接点。因此，孔移至阳极，电子移动到阴极以产生光电流。

The photon absorption intensity and photon energy are directly proportional to each other. When energy of photos is less, the absorption will be more. This entire process is known as Inner Photoelectric Effect.

内在激发和外在激发是光子激发发生的两种方法。当光条中的电子被光子激发到导带上时，内在激发的过程发生。

也请阅读“Different Types of Sensors“

Modes of operation of a Photodiode

Photodiode operates in three different modes. They are:

• Photovoltaic Mode
• 光电传入模式
• Avalanche Diode Mode

让我们简要介绍一下这些模式。

Photovoltaic Mode

否则这被称为零偏置模式。当光电二极管在低频应用和超级光应用中运行时，首选此模式。当光电二极管被光闪光照射时，会产生电压。产生的电压将具有很小的动态范围，并且具有非线性特性。当Photodiode在此模式下配置使用Op-Amp时，温度的变化将大大降低。

光电传入模式

在这种模式下，光电二极管将在反向偏置条件下起作用。阴极将是阳性的，阳极将为负。当反向电压增加时，耗尽层的宽度也会增加。因此，响应时间和连接电容将减少。相比之下，这种操作模式是快速的，并产生电子噪声。

变性放大器用作光二极管的前置放大器。这种放大器的模式保持电压保持恒定，以使照片二极管在光电传导模式下运行。

Avalanche Diode Mode

在这种模式下,雪崩二极管工作在高reverse bias condition. It allows multiplication of an Avalanche Breakdown to each photo-produced electron-hole pair. Hence, this produces internal gain within photodiode. The internal gain increases the device response.

连接外部电路中的光电二极管

A Photodiode operates in a circuit in reverse bias. Anode is connected to circuit ground and cathode to positive supply voltage of the circuit. When illuminated by light, current flows from cathode to anode.

当光电二极管与外部电路一起使用时，它们会连接到电路中的电源。光电二极管产生的电流量将很小。电流值不足以驱动电子设备。因此，当它们连接到外部电源时，它将为电路提供更多的电流。因此，电池用作电源。电池源有助于增加当前价值，这有助于外部设备具有更好的性能

V-I Characteristics of Photodiode

Photodiode operates in reverse bias condition. Reverse voltages are plotted along X axis in volts and reverse current are plotted along Y-axis in microampere. Reverse current does not depend on reverse voltage. When there is no light illumination, reverse current will be almost zero. The minimum amount of current present is called as Dark Current. Once when the light illumination increases, reverse current also increases linearly.

光电二极管的应用

• Photodiodes are used in many simple day to day applications. The reason for their use is the linear response of photodiode to a light illumination. When more amount of light falls on the sensor, it produces high amount of current. The increase in current will be displayed on a galvanometer connected to the circuit.
• 光电二极管有助于借助光耦合器提供电隔离。当两个孤立的电路被光照射时，光相耦合器将使用光学上的回路。但是电路将被电隔离。与常规设备相比，光耦合器很快。
• Photodiodes are also used in safety electronics like fire and smoke detectors. It is also used in TV units.
• When utilized in cameras, they act as photo sensors. It is used in scintillators charge-coupled devices, photoconductors, and photomultiplier tubes.
• 光电二极管也广泛用于众多医疗应用中，例如分析样品，计算机断层扫描的检测器，还用于血液气体监测器中。