What do transistors do? What are the three working areas of transistors
What do transistors do
Transistor, formerly known as semiconductor triode, is a semiconductor device with two PN junctions inside and three lead-out electrodes outside. It has the function of amplifying and switching electrical signals, and is widely used. Both the input stage and the output stage adopt the transistor logic circuit, which is called transistor logic circuit. In books and practical applications, it is called TTL circuit for short. It belongs to one kind of semiconductor integrated circuit, among which TTL NAND gate is the most commonly used. TTL NAND gate is a circuit system composed of several transistors and resistance elements, which is manufactured on a very small silicon chip and packaged into an independent element. Transistor is one of the most widely used devices in semiconductor triode, which is represented by “V” or “VT” (the old characters are “Q”, “GB”, etc.).
Transistor is one of the most critical components of modern electrical appliances. The reason why transistors can be used on a large scale is that they can be produced on a large scale at a very low unit cost.
At present, millions of single transistors are still in use. Most of them are assembled on microchips (chips) together with diodes, resistors and capacitors to make complete circuits. Analog or digital or both are integrated on the same chip. The cost of designing and developing a complex chip is quite high, but when it is produced, the cost of designing and developing a chip is allocated to millions of chips, so the cost of each chip in the market is usually not very expensive. A logic gate contains 20 transistors, compared with 289 million transistors used by an advanced microprocessor in 2005.
Especially after the importance of transistors in military planning and space navigation is increasingly exposed, in order to compete for the dominant position in the field of electronics, countries around the world have launched a fierce competition. In order to realize the miniaturization of electronic equipment, people have given huge financial support to the electronic industry at any cost.
Since Fleming invented the vacuum diode in 1904 and de Forrest invented the vacuum triode in 1906, electronics has developed rapidly as a new discipline. But the real rapid progress of Electronics should start from the invention of transistors. In particular, the appearance of PN junction transistor has opened up a new era of electronic devices and caused a revolution in electronic technology. In a short period of more than ten years, the emerging transistor industry, with its invincible ambition and the reckless momentum of young people, has rapidly replaced the position that the electronic tube industry gained through many years of struggle, and has become the leader in the field of electronic technology.
What are the three working areas of transistors
The output characteristic curve of transistor refers to the relation curve ic = f (UCE) between collector current IC and Collector Emitter Voltage uce in output circuit (collector circuit) when base current IB is constant. Different curves can be obtained under different IB, so the output characteristic curve of transistor is a set of curves. The transistor has three working states, so the output characteristic curve is divided into three working areas
(1) Amplification area
The near horizontal part of the output characteristic curve is the amplification region. The amplification region is also called the linear region because IC is proportional to IB. For NPN type pipe, Ube 0, UBC 0, uce Ube shall be used.
(2) Cut off area
The area below the curve with IB = 0 is called the cut-off area. When IB = 0, ic = ICEO (very small). For NPN type silicon tube, when Ube is 0.5V, the cut-off is started, but in order to make the transistor reliable cut-off, Ube is often 0, and the collector junction is also in reverse bias at the cut-off (UBC 0).
(3) Saturation zone
When uce “Ube”, the collector is in a forward bias (UBC “0), and the transistor is in a saturated state.
In the saturation region, IC and IB are not proportional.
When the transistor is saturated, uce ≈ 0, the connection between emitter and collector is like a switch, and the resistance between them is very small; when the transistor is cut off, IC ≈ 0, the connection between emitter and collector is like a switch, and the resistance between them is very large. It can be seen that the transistor has the function of switch besides amplification.
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