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Transistors and Rectifiers

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The transistor is a three terminal device and consists of three distinct layers.

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Two of them are doped to give one type of semiconductor and the there is the opposite type, i.e. two may be n-type and one p-type, or two may be p-type and one may be n-type.

They are designated either P-N-P (PNP) types of N-P-N (NPN).

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When discussing NPN transistors the N-Type semiconductor material on one side of the wafer is designated an emitter and it is most often connected to a negative electrical current.

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The P-Type material in the middle is the base.

The N-Type material on the other side of the base is called the collector.

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Transistors consist of three terminals: the source, the gate, and the drain.

In the n-type transistor, both the source and the drain are negatively charged and sit on a positively charged well of p-silicon.
When positive voltage is applied to the gate, electrons in the p-silicon are attracted to the area under the gate, forming an electron channel between the source and the drain.
When positive voltage is applied to the gate, electrons in the p-silicon are attracted to the area under the gate, forming an electron channel between the source and the drain.
When positive voltage is applied to the drain, the electrons are pulled from the source to the drain. In this state the transistor is on.
If the voltage at the gate is removed, electrons aren't attracted to the area between the source and drain. The pathway is broken and the transistor is turned off.

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Transistor Advantages

Highly automated manufacturing processes, resulting in low per-unit cost.

Extremely long life.

Higher reliability and greater physical ruggedness.

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Small size and minimal weight, allowing the development of miniaturized electronic devices.

Lower possible operating voltages, making transistors suitable for small, battery-powered applications.

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Looking at the common emitter circuit in the figure: while measuring the voltage and the current, one starts to apply a voltage to the base of the transistor through the base resistor. As the voltage increases from, zero there is no current flowing. At 0.1 volt, no current; 0.2 volt, no current; 0.5 volt, still no current; as the voltage at the base approaches 0.6 volts--where there was no current--all of a sudden a small current starts to be drawn by the base, and the voltage at the base slows its rate of increase--and remains at ~ 0.6 volts. As the voltage from the source increases, the voltage at the base remains ~ 0.6 volts, and the current increases--as well as the corresponding collector current. At some point, as the currents increase, the increase in the collector current starts to slow, until it stops increasing altogether, at this point it is said to be in Saturation (if this transistor was being used as a switch or as part of a logic element, then it would be considered to be switched on).

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Rectifiers

The most popular application of the diode.

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Most electronics need a direct current to function, but the standard form of electricity that is transmitted to homes is alternating current.

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Rectifiers are needed to change the alternating current

into direct current inside the electronics so that they can function correctly.

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Rectification

is the conversion of alternating current (AC) to direct current (DC).

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Rectifiers

This involves a device that only allows one-way flow of electrons, which is exactly what a semiconductor diode does.

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Half-Wave Rectifiers

The simplest kind of rectifier circuit is the half-wave rectifier.

It only allows one half of an AC waveform to pass through to the load.

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Half-wave rectification is a very simple way to reduce power to a resistive load.

Some two-position lamp dimmer switches apply full AC power to the lamp filament for “full” brightness and then half-wave rectify it for a lesser light output.

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Bridge Rectifiers

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The invention of the transistor or semiconductor was probably the most important development that lead to the personal computers amazing growth and what we know of as modern day computers.

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1959

The First I.C.

Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Camera, came up with a solution to the problem of large numbers of components, and the integrated circuit was developed.

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Instead of making transistors one-by-one, several transistors could be made at the same time, on the same piece of semiconductor( a silicon wafer).

Not only transistors, but other electric components such as resistors, capacitors and diodes could be made by the same process with the same materials.

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1970

8080

8–bit processor

4004

4–bit unit

First microprocessor invented at Intel.

First commercial MPU in 1975.

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1981

The IBM PC model 5150 was announced at a press conference in New York on August 12, 1981 and became available for purchase in early Fall 1981.

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The base model retailed for $2880!

This included 64 kilobytes of RAM and a single-sided 160K 5.25" floppy drive.

The IBM PC was powered by a 4.77 MHz Intel 8088 processor.

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Thanks