Ham Radio Store Choosing Transistor Replacements When repairing a circuit, or even building a new one it is often not possible to find the exact electronics component - we tell you how to choose a suitable replacement. Either the type of transistor may not be to hand, or it may not be available. Fortunately it is normally possible to use a replacement transistor type as there is often a considerable degree of overlap between the specifications of different types of transistor, and by looking at the basic specifications it is normally possible to choose the correct transistor replacements. This explanation is focussed on bipolar transistors, but it is possible to apply similar logic to other electronic components including field effect transistors to ensure that suitable replacements can be found.
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See Article History Transistor, semiconductor device for amplifying, controlling, and generating electrical signals.
Deeply embedded in almost everything electronic, transistors have become the nerve cells of the Information Age. There are typically three electrical leads in a transistor, called the emitter, the collector, and the base—or, in modern switching applications, the source, the drain, and the gate. A voltage source such as a battery drives the current, while the rate of current flow through the transistor at any given moment is governed by an input signal at the gate—much as a faucet valve is used to regulate the flow of water through a garden hose.
NMOS transistorNegative-channel metal-oxide semiconductors NMOS employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type.
For positive-channel metal-oxide semiconductors PMOS , all these polarities are reversed. Transistors also began to replace vacuum tubes in the oscillator circuits used to generate radio signals, especially after specialized structures were developed to handle the higher frequencies and power levels involved.
Low-frequency, high-power applications, such as power-supply inverters that convert alternating current AC into direct current DC , have also been transistorized. Some power transistors can now handle currents of hundreds of amperes at electric potentials over a thousand volts. By far the most common application of transistors today is for computer memory chips—including solid-state multimedia storage devices for electronic games , cameras , and MP3 players—and microprocessors , where millions of components are embedded in a single integrated circuit.
In this case the transistor operates as a switch: if a current flows, the circuit involved is on, and if not, it is off. These two distinct states, the only possibilities in such a circuit, correspond respectively to the binary 1s and 0s employed in digital computers. Similar applications of transistors occur in the complex switching circuits used throughout modern telecommunications systems.
The potential switching speeds of these transistors now are hundreds of gigahertz, or more than billion on-and-off cycles per second. Get exclusive access to content from our First Edition with your subscription. Subscribe today Development of transistors The transistor was invented in —48 by three American physicists, John Bardeen , Walter H.
Brattain , and William B. The transistor proved to be a viable alternative to the electron tube and, by the late s, supplanted the latter in many applications. Its small size, low heat generation, high reliability, and low power consumption made possible a breakthrough in the miniaturization of complex circuitry. Motivation and early radar research Electron tubes are bulky and fragile, and they consume large amounts of power to heat their cathode filaments and generate streams of electrons ; also, they often burn out after several thousand hours of operation.
Electromechanical switches, or relays, are slow and can become stuck in the on or off position. For applications requiring thousands of tubes or switches, such as the nationwide telephone systems developing around the world in the s and the first electronic digital computers , this meant constant vigilance was needed to minimize the inevitable breakdowns.
An alternative was found in semiconductors, materials such as silicon or germanium whose electrical conductivity lies midway between that of insulators such as glass and conductors such as aluminum. However, it was military funding for radar development in the s that opened the door to their realization. Electron tubes just did not suffice , and solid-state diodes based on existing copper -oxide semiconductors were also much too slow for this purpose.
Crystal rectifiers based on silicon and germanium came to the rescue. In these devices a tungsten wire was jabbed into the surface of the semiconductor material, which was doped with tiny amounts of impurities, such as boron or phosphorus.
Depending on the nature of the charge carriers and the applied voltage, a current could flow from the wire into the surface or vice-versa, but not in both directions. Thus, these devices served as the much-needed rectifiers operating at the gigahertz frequencies required for detecting rebounding microwave radiation in military radar systems. By the end of World War II , millions of crystal rectifiers were being produced annually by such American manufacturers as Sylvania and Western Electric.
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C4242 NTE Equivalent NTE2312 TRANSISTOR NPN SILIC...