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Difference between Vacuum Tube and Transistor
Vacuum tube and Transistor are types electronic switching devices used a variety of electronic devices and circuits such as computers, communication systems, power supplies, TV, radios, amplifiers, etc. However, both are significantly different from each other based on their technology and operation.
In this article, we will highlight all the points that differentiate a vacuum tube from a transistor. Let's start with some basics of vacuum tubes and transistors.
What is a Vacuum Tube?
A vacuum tube is an electronic device used to control the current flowing in a circuit using a vacuum in a sealed glass tube. Basically, function wise the vacuum tube is an older version of modern transistor.
The practical example of a vacuum is the cathode ray tube (CRT) that was used in early television and computer monitors. An English physicist John Ambrose Fleming was invented the vacuum tube in 1904 which was a basic switching component of all electronic devices at that age.
A vacuum tube consists of two electrodes namely a cathode and an anode, which are enclosed in a sealed glass tube with all the air removed, i.e., there is vacuum inside the tube. The cathode produces electrons and the anode collects these electrons when a potential difference is applied to it. One major disadvantage of the vacuum tube is that it requires a heating element to produce electrons, due to which it consumes much amount of power and burns out quickly.
Although, the vacuum tubes are not completely obsolete, they are still being used in radio stations, UHF TV stations, sound amplifiers, etc.
What is a Transistor?
A transistor is a three terminal semiconductor electronic device that is used for switching purposes in various electronic circuits.
The transistor is the key component of major modern electronic systems. It mainly functions as an electronic switch and an amplifier. The transistor was invented by three American physicists John Bardeen, Walter Brattain and Willian Shockley in 1947.
A typical transistor consists of three layers of semiconductors, when one layer of either P-type or N-type semiconductor is sandwiched between three layers of N-type or P-type semiconductor respectively. A metallic conductor is connected to each of three layers to form the terminal of the transistor. Thus, a transistor has three terminals namely Emitter, Base and Collector.
Based on the construction or the order of sandwiching the layer, the transistors are two types namely NPN transistor and PNP transistor. The transistor is extensively used in many electronic devices such as computers, TVs, smartphones, power supplies, voltage regulators, different types of measuring devices, etc.
Difference between Vacuum Tube and Transistor
As we have already discussed that a vacuum tube and transistor perform same function of switching, i.e. controlling the current flow in a circuit. However, they are different in many aspects; the major differences between vacuum tube and transistor are listed in the following table −
| Basis of Difference | Vacuum Tube | Transistor |
|---|---|---|
| Definition | An electronic device that uses a sealed glass tube and vacuum inside it to control the flow of current in a circuit is called vacuum tube. | A three terminal semiconductor electronic device used for regulation of electronic signals is called a transistor. |
| Construction | A vacuum tube consists of a cathode, an anode, sealed in an air tight glass tube. Inside the tube, vacuum is created. | A transistor consists of three layers of semiconductor materials that are sandwiched to form two PN junctions. Each layer has a connection wire called terminal, hence there are three terminals namely emitter, base and collector. |
| Charge carriers | In vacuum tube, electrons are the only charge carriers that are responsible for conduction. | In transistor, two type of charge carriers exist namely electrons and holes. |
| Emission and flow of charge carriers | In vacuum tube, the electrons are emitted by the heating of cathode and flow towards the anode. | In transistor, the charge carrier are emitted by emitter and flows towards the collector. |
| Principle | Vacuum tube works on the principle of thermionic emission, i.e. a heated metal cathode produces the charge carriers, i.e. electrons. | Transistor works on the principle of solid state physics, i.e. charge carriers are produced by the semiconductor effects. |
| Power consumption | Vacuum tubes consume large amount power. | The power consumption for transistors is less. |
| Wastage of power | In vacuum tube, a lot power is wasted in the form of heat. | In transistors, the wastage of power in the form of heat is less. |
| Physical size | Vacuum tubes are large in size. | The size of transistors is comparatively smaller. |
| Portability | The devices that use vacuum tube are less portable. | The devices that use transistor are easily portable. |
| Voltage | Vacuum tubes require high voltage power supplies. | Transistors require low voltage power supplies. |
| Mechanical strength | As vacuum tubes use glass tube, hence their mechanical strength is less. | Transistors are mechanically stronger than vacuum tubes. |
| Efficiency | Vacuum tubes are comparatively less efficient. | Transistors have very high efficiency compared to vacuum tubes. |
| Voltage gain | For vacuum tubes, the voltage gain is low. | Transistors have high voltage gain. |
| Input impedance | Vacuum tubes have high input impedance. | Transistors have low input impedance. |
| Effect of temperature | The change in temperature slightly affects the performance of a vacuum tube. | The change in the temperature greatly affects the performance of the transistor. |
| Suitability for small signal circuits | Vacuum tubes are not much suitable for small signal circuits due to high power loss. | Transistors are greatly suitable for small signal circuit as they are highly efficient than vacuum tubes. |
| Life span | Vacuum tubes have shorter life span upto thousand hours. | Transistors have relatively longer life span, of many years. |
| Fabrication in ICs | Vacuum tubes cannot be integrated with other elements to form ICs. | Transistors can be integrated to form ICs. |
| Switching time | The switching time of vacuum tube is more, i.e. a vacuum tube does not work instantly when the switched ON because it requires some time for the cathode to get hot. | The switching time of transistor is less, it starts working instantly when switched ON. |
| Replacement | A user of the device can easily replace the vacuum tube. | The replacement of transistor is relatively more difficult as it is soldered at the circuit board. |
| Cost | The cost of vacuum tube is high | Transistors are low cost device. |
Conclusion
Both vacuum tubes and transistors perform almost the same function. The most significant difference between a vacuum tube and a transistor is that a vacuum tube is used in high-power applications while a transistor is used in low-power applications.
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