The voltage as well as current gain of the CE amplifier is high (gain is the factor by which the voltage of current increases from input to output). If the Q point is maintained to be at the center of the load very less or no waveform distortion will take place. Thus voltage across R 3 is coupled to the load and amplification has taken place. Voltage across R 3 is the amplified one and is 180 o apart from the input signal. Therefore voltage across R 3 varies as the collector current is passing through it. When input is applied as shown below the base current starts to vary up and down, hence collector current also varies as I C = β × I B. The Q point is made stable in the active region of the transistor. The BJT is biased in the active region using the necessary biasing components. C 2 is the bypass capacitor which increases the voltage gain and bypasses the R 4 resistor for AC signals.
C 1 and C 3 are coupling capacitors, they are used for blocking the DC component and passing only ac part they also ensure that the DC basing conditions of the BJT remains unchanged even after input is applied. The figure shows a single stage CE amplifier. BJT as Amplifier Single Stage RC Coupled CE Amplifier A very small voltage drop takes place across the BJT and it can be said to be equivalent to a closed switch. There is a small voltage drop across the collector emitter junction of the order of 0.05 to 0.2 V and collector current is very large. The value of base resistance is adjusted such that a large base current flows. In saturation (both junctions are forward biased) a high input voltage is applied to the base. The input voltage is zero so both base and collector currents are zero, hence the resistance offered by the BJT us very high (ideally infinite). In the cutoff region (both junctions are reversed biased) the voltage across the CE junction is very high. Transistor in cutoff region will act as an open switching whereas in saturation will act as a closed switch. Transistor as a Switchįor switching applications transistor is biased to operate in the saturation or cutoff region. There are two types of applications of bipolar junction transistor, switching and amplification. Applications of Bipolar Junction Transistor This is just one portion of an endless history of BJT. For many years transistors were manufactured as individual components until late 1950’s, after which integrated circuits (IC’s) came into existence which placed all components on one single chip. Bardeen and Brattain together with William Shockley were horned by the Nobel Prize in Physics in 1956 for the invention of the transistor effect. The transistors replaced the vacuum tubes and made a dramatic change in the world of electronics. Than Shockley developed the junction transistor (BJT) by pressing together thin slices of different semiconductor materials. Thus the first point contact transistor was made by using germanium, paper clip and razor blades.įigure below shows a replica of the same. In 1947, two physicists John Bardeen and Walter Brattain working at the Bell laboratories found that by making two point contacts very close to one another, they could actually make a three terminal device.
So instead of controlling an electron in vacuum they begin to think of ways to control it in solid materials. Hence, scientists and engineers started thinking of ways to make some other kind of three terminal devices. Size was not the only problem, the tubes consumed large power and sometimes would leak hence were less reliable. In those days a large computer would have many racks filled with tubes which almost occupied a large room. But the major problem was, as the complication of the circuits increased more and more triodes were required to be integrated. The vacuum tube triodes were used in various computer designs till early 1950’s. The light bulb invented by Thomas Edison in the early 1880’s was one of the first uses of vacuum tubes for any electrical applications. In electronics, vacuum tube triodes were used almost for half a century before the BJT’s. Before transistors came into existence vacuum tubes were used. The transistor (BJT) was not the first three terminal devices.
0 kommentar(er)
