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

Un diodo è polarizzato inversamente quando la sua regione di tipo n è collegata al terminale positivo della tensione di alimentazione e la sua regione di tipo p è collegata al terminale negativo.
A tensioni di polarizzazione inversa più basse, la piccola corrente di dispersione attraverso il diodo è principalmente dovuta a portatori di minoranza e la curva IV in questa regione è quasi piatta.
Quando la tensione di polarizzazione inversa aumenta oltre una tensione di soglia, nota come tensione di rottura o tensione di ginocchio, si osserva un forte aumento della corrente per una piccola variazione della tensione.
Nei diodi fortemente drogati ad alte tensioni inverse, il campo elettrico attraverso la regione di svuotamento è abbastanza forte da permettere agli elettroni di valenza di liberarsi dai loro legami. Questo crea coppie elettrone-lacuna, con conseguente aumento significativo della corrente.
Nei diodi leggermente drogati, alte tensioni inverse accelerano i portatori di minoranza attraverso la regione di svuotamento. Si scontrano con gli atomi, creando ulteriori coppie elettrone-lacuna. Questo processo si sviluppa a cascata, portando a un rapido aumento della corrente.
Nei diodi leggermente drogati, la corrente aumenta gradualmente rispetto ai diodi fortemente drogati.

diodo: polarizzazione inversa

Un diodo è polarizzato inversamente quando il terminale positivo di una sorgente di tensione esterna, è collegato al materiale di tipo n e il terminale negativo al materiale di tipo p. Questa configurazione si oppone alla direzione naturale del flusso di corrente attraverso il diodo, aumentando di fatto l'ampiezza della regione di svuotamento e il potenziale di barriera. La condizione di polarizzazione inversa produce una corrente di dispersione minima, dovuta principalmente ai portatori di carica minoritari. Questa perdita diventa significativa quando la tensione inversa supera la tensione termica in condizioni ambientali standard, portando a una curva di risposta corrente-tensione (I-V) appiattita. A differenza dell’aumento esponenziale della corrente osservato nella polarizzazione diretta, l’aumento nella polarizzazione inversa è trascurabile.


Tuttavia, in pratica, la corrente inversa nei diodi spesso supera la corrente di saturazione prevista. Ad esempio, i diodi progettati per piccoli segnali, con correnti di saturazione inversa a livello di femtoampere, possono mostrare correnti inverse a livello di nanoampere. Sebbene questa corrente inversa aumenti leggermente con la tensione inversa, questi cambiamenti sono troppo piccoli per influenzare sensibilmente la curva I-V. Questa corrente inversa ha origine dalla generazione di portatore termico all'interno della giunzione, a seconda delle dimensioni fisiche della giunzione del diodo.


Un forte aumento della corrente inversa si verifica quando la tensione inversa applicata, raggiunge una soglia critica nota come tensione di rottura, specifica per ciascun diodo. Questo fenomeno, rappresentato dal ginocchio sulla curva I-V, indica un aumento sostanziale della corrente con un aumento minimo della tensione.


<img alt="Figure 1" src="/files/ftp_upload/15714/15714_Figure_1.svg" style="height: 200px;">

È essenziale riconoscere che la rottura del diodo non è intrinsecamente dannosa, a condizione che la corrente rimanga all'interno della sua area operativa sicura, generalmente definita dalla sua massima capacità di dissipazione di potenza nella scheda tecnica. Per prevenire potenziali danni è necessario un circuito esterno, progettato per limitare la corrente inversa a livelli di sicurezza. I diodi Zener, progettati per funzionare nella regione di guasto per la regolazione della tensione, esemplificano i diodi che funzionano in sicurezza in queste condizioni.

Diodo: Polarizzazione Inversa

Un diodo è polarizzato inversamente quando la sua regione di tipo n è collegata al terminale positivo della tensione di alimentazione e la sua regione di tipo p è collegata ...

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

Diodes

Diodi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 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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