Name: diode reverse current and breakdown
Uploaded: 2024-07-08T13:20:19.000Z
Duration: 1 min 14 s
Channel: JoVE

当二极管的n型区连接到电源电压的正极，而p型区连接到负极时，该二极管处于反向偏置状态。
在较低的反向偏置电压下，通过二极管的微小漏电流主要由少数载流子引起，该区域的电流-电压曲线几乎平坦。
当反向偏置电压超过某个阈值电压（称为击穿电压或拐点电压）时，电压发生微小变化即可观察到电流急剧上升。
在高掺杂二极管中，当施加高反向电压时，耗尽区内的电场足够强，使得价电子能够挣脱化学键的束缚。这会生成电子-空穴对，导致电流显著增加。
在轻掺杂二极管中，高反向电压会加速少数载流子穿过耗尽区。这些载流子与原子碰撞，产生额外的电子-空穴对。该过程发生级联效应，导致电流迅速增加。
在轻掺杂二极管中，电流的增长比在重掺杂二极管中更为缓慢。

二极管：反向偏置

Diode: Reverse bias

当外部电压源的正极连接到 n 型材料、负极连接到 p 型材料时，二极管便会被反向偏置。这种配置与电流流过二极管的自然方向是相反的，从而有效地增加了耗尽区的宽度和势垒电位。在反向偏置条件下能够产生最小的漏电流，这主要是由于少数电荷载流子造成的。当反向电压超过标准室温条件下的热电压时，漏电流将会变得很大，从而导致电流-电压（I-V）的响应曲线趋于平缓。与正向偏置中观察到呈指数增加的电流不同，反向偏置中增加的电流可以忽略不计。
然而，在实际应用中，二极管中的反向电流往往会超过预测的饱和电流。例如，为小信号设计的二极管中具有飞安级的反向饱和电流，但可能会表现出纳安级的反向电流。虽然这种反向电流会随着反向电压的增加而略有增加，但这些变化太小，不足以对 I-V 曲线产生显著的影响。这种反向电流源于结内的热载流子的产生，这具体取决于二极管结的物理尺寸。
当施加的反向电压达到每个二极管特有的临界阈值（称为击穿电压）时，反向电流就会急剧增加。这种现象通常会由 I-V 曲线上的拐点来进行表示，这标志着电流会大幅上升，而电压却增加较少。
<img alt="Figure 1" src="/files/ftp_upload/15714/15714_Figure_1.svg" style="text-align: center; height: 200px;">
必须清晰的认识到，只要电流保持在其安全工作区内（通常由数据表中的最大功率耗散的能力来进行定义的），二极管击穿本身并不会造成损害。为防止出现潜在的损坏，则有必要设计用于将反向电流限制在安全水平的外部电路。齐纳二极管是在这些条件下安全工作的二极管的典范，其中的设计使其能够在电压调节的击穿区域内工作。

当二极管的n型区连接到电源电压的正极，而其p型区连接到……时，该二极管处于反向偏置状态。

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 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 diode’s I-V curve becomes nearly flat, unlike the steep rise seen in forward bias.

Real diodes often show more reverse current than the ideal saturation current predicts. Small-signal diodes with femtoampere-level reverse saturation current may still measure nanoampere-level reverse current. This current can rise a little as reverse voltage increases, but the change is usually too small to affect the I-V curve much. It comes from thermal carrier generation in the junction and depends on the junction’s physical size.

A sharp increase in reverse current begins at the breakdown voltage. This is the critical reverse voltage where the I-V curve shows a knee and current rises quickly with little extra voltage. Breakdown is not always damaging if the current stays within the diode’s safe operating area, which is usually tied to the maximum power dissipation listed in the datasheet. External circuitry is used to keep reverse current safe, and Zener diodes are designed to work in the breakdown region for voltage regulation.

Diode Reverse Current and Breakdown

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

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

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 reverse bias creates leakage current, why the diode I-V curve flattens, and what happens at breakdown voltage, including safe use in Zener diodes.

Diode Reverse Current and Breakdown | 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 Reverse Current and Breakdown

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