Name: diode current in forward bias
Uploaded: 2024-07-08T13:20:19.000Z
Duration: 1 min 20 s
Channel: JoVE

当二极管的 p 型区域连接到电源电压的正极端子，并且其 n 型区域连接到负极端子时，二极管是正向偏置的。 
正向电流-电压特性显示偏置电压低于 0.7 V 的电流可以忽略不计，称为切入电压。然而，当偏置电压略微超过 0.7 V 时，二极管中的电流急剧上升。
因此，具有不同额定电流的全导通二极管在不同电流下将出现 0.7 伏的压降。
二极管的电流-电压关系涉及饱和电流，饱和电流取决于温度和横截面积。
涉及玻尔兹曼常数和电子电荷大小的热电压以温度表示。
对于有效的正向电流，二极管方程简化为指数形式，并以热电压表示为对数。
比较两个二极管电压的电流，该方程使用以 10 为基数的对数，表明电流变化 10 倍对应于二极管两端约 60 毫伏的压降。

二极管：正向偏置

在半导体器件中，二极管在引导电流流动方面发挥着至关重要的作用，其工作原理主要分为正向偏置和反向偏置。当二极管的 p 型区域连接到电池的正极、n 型区域连接到负极时，那么该二极管就会被称为正向偏置。这种配置降低了二极管内的势垒，从而使电流能够轻松地从 p 型区域流向 n 型区域。
二极管在正向偏置下的行为是由其 I-V 特性所决定的，而 I-V 特性会受到二极管的材料、温度和物理尺寸所产生的影响。在正向偏置时，二极管的电流 (I_D) 可以用二极管方程来进行描述：
<img alt="Equation 1" src="/files/ftp_upload/15713/15713_Equation_1.svg" style="text-align: center; height: 26px;">
其中，I_S 为饱和电流，q 为电子电荷，V_D 为施加在二极管上的电压，n 为发射系数，k 为玻尔兹曼常数，T 为结温。热电压 V_T （kT/q）能够测量电荷载流子穿过二极管所需的能量，在室温下的值大约为 26 mV。
<img alt="Figure 1" src="/files/ftp_upload/15713/15713_Figure_1.svg" style="text-align: center; height: 200px;">
当电压低于切入电压（硅二极管的切入电压通常为 0.7 V）时，二极管中的电流便可以忽略不计。在正向偏置的状态下，正向电流每变化十倍，二极管电压就会发生大约 60 mV 的变化。饱和电流（I_S）会随着温度和二极管的横截面积而发生变化，其中的温度每增加 10°C 就会增加一倍。由于 I_S 和 V_T 都与温度有关，因此在恒定电流下，温度每升高 1°C，那么二极管的压降就会下降大约 2 mV，这一特性在电子温度计等温度传感电路中得到了利用。对于整流器、信号混频器和稳压器等以二极管为核心元件的电子产品来说，了解以上这些特性是至关重要的。

当二极管的 p 型区域连接到电源电压的正极端子并且其 n 型区域连接到电源电压的正极端子时，二极管是正向偏置的。

Education

教育

JoVE Core

Electrical Engineering

电气工程

Unit 1

第一单元

Diodes

二极管

KEY TERMS AND CONCEPTS

关键术语与概念

Diode: Forward bias

diode current in forward bias

Diode current in forward bias depends on how the p-type and n-type regions are connected to a battery. When the p-type region is tied to the positive terminal and the n-type region to the negative terminal, the diode is forward-biased. This setup lowers the potential barrier inside the diode and lets current move easily from the p-type side to the n-type side.

The current-voltage behavior of a forward-biased diode is described by its I-V characteristics. These characteristics depend on the diode material, temperature, and physical size. The diode current can also be written using the diode equation, which includes saturation current, electron charge, applied diode voltage, emission coefficient, Boltzmann's constant, and junction temperature.

Thermal voltage, written as kT/q, shows the energy needed to move charge carriers across the diode. At room temperature, it is about 26 mV. A silicon diode also shows very little current below its cut-in voltage, which is typically 0.7 V.

In forward bias, the diode voltage changes by about 60 mV for every decade change in forward current. The saturation current changes with temperature and with the diode's cross-sectional area. It doubles for every 10°C increase. Because of the temperature effect on saturation current and thermal voltage, the diode voltage drop falls by about 2 mV for each 1°C rise in temperature at a constant current.

This temperature behavior is useful in circuits that measure heat, such as electronic thermometers. Diodes are also important in rectifiers, signal mixers, and voltage regulators. Understanding forward bias helps explain why diodes are key parts of many electronics.

Diode Current in Forward Bias

the ideal diode

Ideal Diode I-V Curve and Rectification

An ideal diode is a simple model of a semiconductor diode used to show how current moves through circuits. A diode has two terminals. The anode is positive, and the cathode is negative. In this model, current can flow only in one direction. When a positive voltage is applied to the anode relative to the cathode, the diode is forward-biased. In that state, it conducts current. When the cathode is at a higher potential than the anode, the diode is reverse-biased. It then blocks current and acts...

diode: forward bias

Diode current in forward bias depends on how the p-type and n-type regions are connected to a battery. When the p-type region is tied to the positive terminal and the n-type region to the negative terminal, the diode is forward-biased. This setup lowers the potential barrier inside the diode and lets current move easily from the p-type side to the n-type side. The current-voltage behavior of a forward-biased diode is described by its I-V characteristics. These characteristics depend on the...

diode: reverse bias

Diode Reverse Current and Breakdown

A diode in reverse bias blocks current flow and widens its depletion region. In this setup, the positive terminal of the power source connects to the n-type material, and the negative terminal connects to the p-type material. The reverse connection also raises the barrier potential, so current stays very small. The small reverse current is called leakage current. It comes mainly from minority charge carriers. At room temperature, once the reverse voltage is above the thermal voltage, the...

zener diodes

Zener Diode Voltage Regulation

Zener diodes are semiconductor devices used to hold voltage steady in reverse bias. In reverse breakdown, current flows into the cathode and makes it positive relative to the anode. This behavior is different from a conventional diode and is the reason Zener diodes are useful in voltage regulation. A Zener diode has a nearly vertical current-voltage, or I-V, curve above a threshold called the knee current. That shape lets it keep a fairly stable voltage over a wide range of currents.

modeling of diode forward characteristics

modeling-of-diode-forward-characteristics

Diode Forward Bias: I-V Curve and Models

Diode forward bias is analyzed with the current-voltage, or I-V, curve and two common circuit models. These models help describe how a diode behaves when current flows in the forward direction. They are useful for electronic circuit design and analysis. The exponential diode model is used when the source voltage rises above 0.5 volts. At that point, the diode current increases exponentially above the saturation current. The I-V curve shows this nonlinear response as the forward voltage...

small-signal diode model

Diode Bias and Small-Signal Response

Diode bias and small-signal response describe how a diode behaves when a steady DC voltage and a tiny changing signal act on the same circuit. The DC bias sets the diode’s operating point, or Q point. Around that point, the diode current and voltage follow an exponential I-V relationship. A small time-varying signal can be added on top of the DC bias to study how the diode responds to small changes. When the signal voltage is much smaller than the thermal voltage, the diode’s behavior can be...

modeling of diode reverse characteristics

modeling-of-diode-reverse-characteristics

Zener Diode Load-Line Modeling

Zener diode load-line modeling shows how a reverse-biased diode sets a steady voltage in a circuit. Zener diodes use reverse breakdown in a controlled way, so they can hold a fixed voltage across their terminals. This makes them useful for voltage regulation. When the reverse voltage rises above the Zener voltage, or VZ, the diode enters the breakdown region. In this region, the current-voltage, or I-V, curve becomes nearly vertical after the knee current, IZ, is reached. That means the...

half wave rectifier

Single-Diode AC to DC Conversion

Single-diode AC to DC conversion uses a half-wave rectifier to change alternating current into a unidirectional voltage. The circuit is simple. It uses one diode in series with a load resistor and an AC power source. The diode controls the current because it allows flow in only one direction. During the positive half-cycles of the AC input, the diode is forward-biased. When the input voltage is greater than the diode threshold, current flows and an output voltage appears across the load...

full wave rectifier

AC to DC Conversion with Full-Wave Rectifiers

A full-wave rectifier converts alternating current, or AC, into direct current, or DC. It is more efficient than a half-wave rectifier. The circuit usually uses a center-tapped transformer, two diodes, and a load resistor. The center-tapped transformer is the key part of the circuit. Its secondary winding is split into two equal voltages with opposite polarities. That split lets the rectifier use both halves of the AC input waveform. During the positive half-cycle of the AC signal, diode D1...

bridge rectifier

AC to DC Conversion with Bridge Diodes

A bridge rectifier converts alternating current (AC) into direct current (DC) using four diodes arranged in a bridge layout. It is used to turn both halves of the AC waveform into a single-direction output. That makes it an important part of many electronics circuits. During the positive half-cycle, diodes D1 and D2 conduct. Current then flows through the load resistor R. At the same time, D3 and D4 are reverse-biased, so they do not conduct. The action switches during the negative half-cycle.

clipper circuit

Dual Diode Wave Clipping

Dual diode wave clipping uses diodes and biasing batteries to reshape an AC signal. A clipper circuit is a wave-shaping device that changes waveform parts without changing the whole signal. It is commonly used in television and radar communication systems to improve waveform modulation in transmitters and receivers. A dual-clipper setup uses two ideal diodes, two biasing batteries, and a resistor connected in parallel. The circuit works by responding to the phase of the input AC signal. The...

clamper circuit

DC Restorer for Waveform Level Shifting

A clamper circuit, or DC restorer, shifts a waveform up or down by adding a DC level. It is a special form of rectifier circuit. In this setup, the output is taken across the diode instead of across the capacitor. The circuit works well with square wave inputs and other pulse signals. The diode direction lets the capacitor charge to the most negative peak of the input signal. After that, the diode stops conducting. The capacitor then holds that voltage at a steady value. As a result, the...

voltage doubler circuit

How a Voltage Doubler Raises AC Output

A voltage doubler circuit raises the output voltage by using a clamping section and a rectifier section. The clamping section includes a capacitor, C1, and a diode, D1. The rectifier section includes a second diode, D2, and a capacitor, C2. The circuit starts working when a sinusoidal input signal enters the clamping section. Under ideal conditions, this stage clamps the positive peaks at zero volts. It also lets the negative peak reach a magnitude that is twice the input amplitude. That...

schottky barrier diode

Fast Switching in Schottky Diodes

Schottky barrier diodes use a metal-semiconductor junction to control current flow. They are built by combining a metal layer with a moderately doped n-type semiconductor. This contact creates the Schottky barrier, which gives the diode its one-way current behavior. When the metal touches the semiconductor, charge transfer occurs. The Fermi levels of the two materials align, and a depletion region forms near the contact area. In an n-type semiconductor, this region contains uncompensated...

key terms and concepts

Learn how a forward-biased diode conducts current, how its voltage changes with current and temperature, and why these properties matter in circuits.

Diode Current in Forward Bias | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Diode Current in Forward Bias

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