Transistor as an amplifier
The common-emitter amplifier is designed so that a small change in voltage in (Vin) changes the small current through the base of the transistor and the transistor's current amplification combined with the properties of the circuit mean that small swings in Vin produce large changes in Vout.
Various configurations of single transistor amplifier are possible, with some providing current gain, some voltage gain, and some both.
From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. The first discrete transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.
Modern transistor audio amplifiers of up to a few hundred watts are common and relatively inexpensive.
Advantages
The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are
- Small size and minimal weight, allowing the development of miniaturized electronic devices.
- Highly automated manufacturing processes, resulting in low per-unit cost.
- Lower possible operating voltages, making transistors suitable for small, battery-powered applications.
- No warm-up period for cathode heaters required after power application.
- Lower power dissipation and generally greater energy efficiency.
- Higher reliability and greater physical ruggedness.
- Extremely long life. Some transistorized devices have been in service for more than 30 years.
- Complementary devices available, facilitating the design of complementary-symmetry circuits, something not possible with vacuum tubes.
- Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications.
Limitations
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Silicon transistors do not operate at voltages higher than about 1,000 volts (SiC devices can be operated as high as 3,000 volts). In contrast, electron tubes have been developed that can be operated at tens of thousands of volts. -
High power, high frequency operation, such as that used in over-the-air television broadcasting, is better achieved in electron tubes due to improved electron mobility in a vacuum. -
Silicon transistors are much more sensitive than electron tubes to an electromagnetic pulse, such as generated by an atmospheric nuclear explosion.
Rooselvet Ramirez EES
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