2N4903

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The 2N4903 is a single NPN planar silicon transistor in a small plastic TO-92 package with 2.54 mm pin pitch. It is mainly used for general purpose switching applications. This article will cover the application area and working principle of 2N4903 transistors.

Application Area of 2N4903 Transistor

2N4903 transistor is an NPN planar silicon transistor in small plastic TO-92 package mainly used for general purpose switching applications. It is often used in audio amplifier circuits, small power supplies, low noise amplifiers, audio amplifiers, and so on. The 2N4903 typically features a low current gain of around 20-120 and is capable of operating at high collector currents up to 500mA for consumer electronics. It has also been used in radio frequency amplifiers, as it has a reasonably high frequency response to meet the demands of modern consumer electronics.

Working Principle of 2N4903 Transistor

The 2N4903 is a general purpose NPN transistor and the working principle is similar to other NPN transistors. There are three leads which are the collector (C), base (B), and emitter (E) leads. When a small base current (IB) is applied to the base terminal, it controls a large emitter current (IE) flowing from the emitter terminal. This means that the current flow from the collector to the emitter is controlled by the base terminal. The base current flows through the semiconductor crystal and the electron-hole pairs that are produced turn the transistor “on”.

From the collector terminal, the voltage between collector and emitter is controlled by turning the transistor on or off. When the transistor is on, it acts as a current amplifier and allows a large current to flow from collector to emitter. When it is off, the voltage between collector and emitter will be high. Thus, the base-emitter junction acts as a switch between the collector and emitter of the transistor.

The working of 2N4903 transistor is explained through the construction, operation and characteristics. TO-92 transistor is a three-terminal transistor constructed in a low cost plastic package. It contains three layers of semiconductor material enclosed in an epoxide mold. This three-layer transistor contains emitter, base and collector region. These layers are protected by a polyester (plastic) enclosure. Collector layer is heavily doped to take more current, base layer is lightly doped and emitter layer is moderately doped.

When the base terminal is forward biased and the collector terminal is reverse biased, electrons at the emitter and holes at the collector start to move. This results in avalanche breakdown, in which electrons and holes flow across the base region generating an amplified current. This amplified current flows from collector to emitter terminal resulting in an increase in collector-emitter voltage and current. As the collector is reverse biased, the collector-emitter voltage will drop when the transistor is turned off. This transistor can operate at collector current up to 500mA.

Conclusion

The 2N4903 is a general purpose NPN planar silicon transistor in a small plastic TO-92 package. It is mainly used for general purpose switching applications with a low current gain of around 20-120, and is capable of operating at high collector currents up to 500mA for consumer electronics. The transistor works on the principle of avalanche breakdown in which electrons and holes flow across the base region generating an amplified current with the help of reverse biasing.

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