BC638,126

The BC638/126 are a pair of complementary NPN/PNP transistors whose applications and working range from each other to form a complete set of digital switching devices. In this article, we will provide a comprehensive overview of their field application and working principles.

General Outline

The BC638/126 are part of a family of discrete bipolar junction transistors (BJT\'s) that are typically applied in digital systems. The BC638 is an NPN transistor, while the BC126 is its complementary PNP transistor. Both BJT’s offer internal protection against excessive currents and voltages. They are usually bought as a pair, since their internals and external functionality are symmetrical and thus compatible with one another.

Field of Application

The main application areas of these transistors are in circuit (electronic) design, microprocessors and computer systems, analog-to-digital converters, memory and communication. They find significant applications in voltage and power control, as well as for noise and interference filtering and for digital switching.

Due to their low cost and operation, these transistors are extensively used for general purpose switching in digital applications. They can easily handle low current (less than 1A) digital control signals and provide high noise immunity. They are often used in place of small-scale relays and can perform high speed switching in a reliable manner.

Working Principles

The working principle of the BC638/126 transistors is based on the properties of BJT\'s. A BJT is made of three junctions: the emitter, base, and collector. When a voltage is applied between the emitter and collector, a current begins to flow. The amount of current flow is determined by the voltage applied to the base junction, which essentially controls the amount of current flowing through the transistor.

In the case of the BC638/126 transistors, the emitter-base junction is forward biased, which allows current to flow from the emitter to the base. This current is then amplified by the collector-base junction and the amplified current is then output at the collector. The amount of amplification depends on the current gain (beta) of the transistor and the current flowing from the emitter to the base.

In terms of digital switching, the BC638/126 transistors can be used to control the current flow of a digital signal. When a voltage is applied to the base, the transistor will pass the current through the collector and the current will flow through the device, thus allowing for digital switching.

Conclusion

The BC638/126 transistors can be used for a range of applications, from memory and communications to digital switching, voltage and power control. These transistors offer high noise immunity, low cost and can provide reliable, high-speed switching. The working principle is based on the BJT, wherein the emitter-base junction is forward biased, allowing current to flow from the emitter to the base, which is then amplified and output at the collector.