Name: depletion mosfet channel control
Uploaded: 2024-07-08T13:20:42.000Z
Duration: 1 min 20 s
Channel: JoVE

I MOSFET in modalità di svuotamento sono già attivi senza polarizzazione del gate, ma necessitano di una tensione gate-source per essere disattivati.
Funzionano come i JFET, in cui il canale drain-source è intrinsecamente conduttivo a causa del drogaggio del canale. In questo modo si crea un percorso a bassa resistenza tra lo scarico e la sorgente, consentendo alla corrente di fluire senza alcuna polarizzazione del gate.
Per i MOSFET a deplezione a canale n, le caratteristiche di drain mostrano che una tensione di gate positiva crescente allarga il canale, aumentando così la corrente di drain.
Man mano che la tensione di gate diventa più negativa, la corrente di drain diminuisce. Questo comportamento è inverso per i MOSFET a deplezione del canale p.
La tensione di soglia del gate è la tensione gate-source alla quale il canale si chiude completamente, interrompendo il flusso di corrente.
La corrente di saturazione è la corrente massima che può fluire attraverso il dispositivo a una tensione gate-to-source pari a zero.
I MOSFET di svuotamento funzionano come un normale interruttore acceso, il che li rende utili nei circuiti logici digitali come resistori di carico.
Sono ampiamente utilizzati nei circuiti di alimentazione ausiliaria di avviamento, nei circuiti di spazzamento della tensione, nei circuiti di monitoraggio della corrente e nei relè a stato solido, tra le altre applicazioni.

mosfet: modalità impoverimento

I MOSFET in modalità impoverimento rappresentano un sottoinsieme unico della tecnologia MOSFET, funzionando in modo fondamentalmente diverso dalle loro controparti in modalità potenziata. A differenza dei MOSFET di potenziamento, che richiedono una tensione gate-source (V_gs) positiva per l'accensione, i MOSFET in modalità impoverimento sono dispositivi intrinsecamente conduttivi e "normalmente accesi".


La caratteristica principale dei MOSFET a impoverimento è la loro capacità di condurre corrente tra i terminali di drain e source, senza polarizzazione del gate. Questa conduttività intrinseca è dovuta al drogaggio del canale, che crea un percorso a bassa resistenza per il flusso di corrente. Il dispositivo funziona in modo simile ai transistor a effetto di campo a giunzione (JFET), dove la conduttività del canale è predeterminata dalle proprietà del materiale.


Nei MOSFET in modalità impoverimento a canale n, l'applicazione di una V_gs positiva aumenta la larghezza del canale, aumentando così la corrente di drain (i_d). Al contrario, applicando una V_gs negativa si restringe il canale, riducendo l'i_d. Questo comportamento è l'opposto per i MOSFET a impoverimento a canale p, dove un V_gs positivo diminuisce l'i_d e un V_gs negativo lo aumenta.


Un parametro critico per questi MOSFET è la tensione di soglia di gate (V_TH), la V_gs specifica alla quale il canale si chiude completamente, interrompendo il flusso di corrente. Un'altra caratteristica fondamentale è la corrente di saturazione, la corrente massima che scorre attraverso il MOSFET a zero V_gs.


A causa del loro stato "on" predefinito, i MOSFET in modalità di esaurimento sono particolarmente utili in applicazioni come amplificatori di potenza per trasmettitori radio. In questo caso consentono la trasmissione continua del segnale, mantenendo la presenza del segnale, finché una tensione di controllo non spegne esplicitamente il dispositivo. Questa capacità di rimanere continuamente attivi, rende i MOSFET in modalità di esaurimento parte integrante delle applicazioni che richiedono un funzionamento affidabile e ininterrotto.

MOSFET: Modalità Impoverimento

I MOSFET in modalità di svuotamento sono già attivi senza polarizzazione del gate, ma necessitano di una tensione gate-source per essere disattivati.
Funzionano come i JFET, dove la sorgente di scarico ...

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MOSFET: Depletion Mode

depletion mosfet channel control

Depletion-mode MOSFETs are normally on transistors with a built-in channel that conducts current without gate bias. They work differently from enhancement-mode MOSFETs, which need a positive gate-source voltage, or V gs, to turn on. In a depletion device, the channel is already open because the channel doping creates a low-resistance path between the drain and source.

These devices behave much like junction field-effect transistors, or JFETs. The channel conductivity is set by the material itself. For an n-channel depletion MOSFET, a positive V gs makes the channel wider and increases drain current, or i d. A negative V gs narrows the channel and reduces i d.

A p-channel depletion MOSFET responds in the opposite way. A positive V gs lowers i d, while a negative V gs raises it. The gate threshold voltage, or V TH, is the V gs value that closes the channel completely and stops current flow. Another important value is the saturation current, which is the maximum current at zero V gs.

Because they stay on by default, depletion-mode MOSFETs are useful in circuits that need continuous operation. One example is a power amplifier in a radio transmitter, where the signal keeps flowing until a control voltage turns the device off. This makes depletion-mode MOSFETs a strong choice for reliable, uninterrupted signal control.

Depletion MOSFET Channel Control

bipolar junction transistor

BJT Structure and Carrier Flow

Bipolar junction transistors are important parts of electronic circuits. They help make amplifiers, memories, and microprocessors work. A BJT can be built as either NPN or PNP, depending on its doping pattern, which means the type of impurities added to the material. A BJT has three layers: the emitter, base, and collector. It also has two p-n junctions, so the device has a sandwich-like structure. The emitter is heavily doped so it can inject charge carriers into the base. The base is very...

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BJT Frequency Limits and Gain Drop

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BJT as a Digital On-Off Switch

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BJT Amplifier Gain and Input Resistance

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JFET Output Regions and Current Control

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MOSFET Structure and Operating Regions

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MOSFET Switching in Enhancement Mode

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mosfet: depletion mode

Depletion-mode MOSFETs are normally on transistors with a built-in channel that conducts current without gate bias. They work differently from enhancement-mode MOSFETs, which need a positive gate-source voltage, or V gs, to turn on. In a depletion device, the channel is already open because the channel doping creates a low-resistance path between the drain and source. These devices behave much like junction field-effect transistors, or JFETs. The channel conductivity is set by the material...

mosfet amplifiers

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small-signal analysis of mosfet amplifiers

small-signal-analysis-of-mosfet-amplifiers

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key terms and concepts

Learn how depletion-mode MOSFETs control channel width, drain current, and threshold voltage, and why their normally on design suits radio transmitters.

Depletion MOSFET Channel Control | 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

Depletion MOSFET Channel Control

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