Name: pnp bjt current flow in active mode
Uploaded: 2024-07-08T13:20:31.000Z
Duration: 1 min 15 s
Channel: JoVE

Consider a PNP transistor in a common-base configuration, operating in active mode.
Forward biasing reduces the emitter-base potential, enabling the diffusion of holes from the emitter to the base and electrons from the base to the emitter. At the same time, the leakage current flows into the emitter.
The injected holes diffuse towards the collector, with a few undergoing recombination with electrons in the base region.
Additionally, the thermally generated electrons drift from the collector to the base, further contributing to the collector current.
The difference between the emitter and collector currents forms part of the base current, which helps maintain charge neutrality in the base region.
By utilizing the terminal currents, the common-base current gain for the BJT is determined.
Here, the first term signifies emitter efficiency, while the second term represents the base transport factor. For a well-designed transistor, both terms should approach unity.
When expressing the collector current in terms of current gain, the second term corresponds to the leakage current between the collector and the base.

werkingsprincipe van bjt

Een bipolaire junctie transistor (BJT), specifiek een PNP-transistor in een gemeenschappelijke basisconfiguratie, versterkt of schakelt effectief elektronische signalen door de stroom van ladingsdragers te regelen. Deze discussie concentreert zich op de werking ervan in de actieve modus.


In de PNP-configuratie is de emitter zwaar gedoteerd met positieve ladingsdragers (gaten), terwijl de basis licht gedoteerd is met negatieve ladingsdragers (elektronen). Deze opstelling maakt een voorwaartse bias over de emitter-basisovergang mogelijk, waardoor de potentiële barrière wordt verminderd en gaten van de emitter naar de basis kunnen diffunderen. Deze gaten proberen vervolgens in de richting van de collector te lopen. Tijdens deze reis recombineren sommige gaten met elektronen in de basis, waardoor het aantal dragers dat de collector bereikt, afneemt en bijdraagt ​​aan de basisstroom. Tegelijkertijd bewegen de thermisch gegenereerde elektronen van de collector naar de basis, waardoor de collectorstroom toeneemt.


De primaire component van de emitterstroom zijn deze diffunderende gaten. De basisstroom komt voort uit het verschil tussen de emitterstroom en de collectorstroom, wat cruciaal is voor het handhaven van de ladingsneutraliteit in de basis. De efficiëntie van de transistor wordt gemeten aan de hand van de stroomversterking, die twee kritische factoren omvat: de emitterefficiëntie en de basistransportfactor. Het emitterrendement geeft het deel van de door de emitter geïnjecteerde dragers aan die bijdragen aan de uitgangsstroom. De basistransportfactor weerspiegelt daarentegen het aandeel van deze vervoerders dat de verzamelaar bereikt. Idealiter zouden beide waarden de eenheid moeten benaderen, wat een efficiënt dragertransport en minimale recombinatie betekent.


Bovendien wordt elke lekstroom tussen de collector en de basis wanneer de emitter-basisovergang open is, meegenomen in de berekening van de collectorstroom in termen van stroomversterking. Deze lekkage duidt op een operationele inefficiëntie, die de prestaties van de transistor in elektronische circuits beïnvloedt.

Werkingsprincipe van BJT

Consider a PNP transistor in a common-base configuration, operating in active mode.
Forward biasing reduces the emitter-base potential, enabling the ...

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Working Principle of BJT

pnp bjt current flow in active mode

PNP bipolar junction transistors control current flow by moving charge carriers between the emitter, base, and collector. In a common-base setup, the transistor can amplify or switch electronic signals when it operates in active mode.

In a PNP transistor, the emitter is heavily doped with holes, which are positive charge carriers. The base is lightly doped with electrons, which are negative carriers. A forward bias across the emitter-base junction lowers the potential barrier and lets holes diffuse from the emitter into the base.

After entering the base, some holes recombine with electrons there. That recombination reduces the number of carriers that reach the collector and creates part of the base current. At the same time, thermally generated electrons from the collector move toward the base, which adds to the collector current.

The emitter current is mainly made up of the holes that diffuse from the emitter. The base current is the difference between the emitter current and the collector current. This difference helps maintain charge neutrality in the base.

The current gain of the transistor depends on emitter efficiency and the base transport factor. Emitter efficiency describes how many injected carriers from the emitter contribute to the output current. The base transport factor shows how many of those carriers reach the collector, and both values should ideally be close to unity for efficient transport and low recombination.

Any leakage current between the collector and base when the emitter-base junction is open is also included in the collector current used for current gain. This leakage shows some loss in efficiency and affects transistor performance in electronic circuits.

PNP BJT Current Flow in Active Mode

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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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Bipolar Junction Transistor (BJT) configurations are defined by which terminal is shared by the input and output circuits. The shared terminal can be the base, emitter, or collector. Each setup has different electrical behavior and fits different circuit needs. In the common base configuration, the base is the common terminal. This setup has high voltage gain, so it can work well in single-stage amplifier circuits such as microphone pre-amplifiers. It also reduces the input current signal...

working principle of bjt

PNP bipolar junction transistors control current flow by moving charge carriers between the emitter, base, and collector. In a common-base setup, the transistor can amplify or switch electronic signals when it operates in active mode. In a PNP transistor, the emitter is heavily doped with holes, which are positive charge carriers. The base is lightly doped with electrons, which are negative carriers. A forward bias across the emitter-base junction lowers the potential barrier and lets holes...

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The Bipolar Junction Transistor (BJT) in a common-emitter setup is studied by measuring its current-voltage curves. These measurements show how the transistor responds when voltage and current are changed in a controlled way. They are key to understanding how a BJT works in electronic circuits. The input characteristics are found by varying the base-emitter voltage while keeping the collector-emitter voltage constant. This test shows a Shockley-type relationship between the collector current...

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key terms and concepts

Learn how a PNP BJT in common-base active mode moves holes and electrons, forms emitter and base current, and uses current gain.

PNP BJT Current Flow in Active Mode | 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

PNP BJT Current Flow in Active Mode

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