Difference between triode and MOS transistor when used as switch

What is the difference between triodes and MOS switches in circuit design? Working properties:
1. Triode is controlled by current and MOS is controlled by voltage
2. Cost problem: triode is cheap, MOS tube is expensive.
3. Power consumption problem: large triode loss.
4. Driving capability: MOS tube is often used for power switch and high current local switch circuit.
In fact, triode is relatively cheap and easy to use. It is often used in digital circuit switch control.
MOS transistor is used in high-frequency and high-speed circuits, high current occasions, and places sensitive to base or drain control current.
Generally speaking, for low-cost occasions, triode shall be considered first for ordinary applications, and MOS transistor shall be considered if not
In fact, it is wrong to say that current control is slow and voltage control is fast. To really understand, you have to understand how bipolar transistors and MOS transistors work. The triode works by the movement of carriers. Taking the emitter follower of NPN tube as an example, when the base is applied with or without voltage, the PN junction composed of the base region and the emission region prevents the diffusion movement of multipons (the base region is holes and the emission region is electrons). At this PN junction, an electrostatic field (i.e. built-in electric field) from the emission region to the base region will be induced, When the direction of the base applied positive voltage is that the base region points to the emission region, when the electric field generated by the base applied voltage is greater than the built-in electric field, the carrier (electron) in the base region may flow from the base region to the emission region. The minimum value of this voltage is the forward conduction voltage of the PN junction (generally considered as 0.7V in Engineering). However, at this time, there will be charges on both sides of each PN junction. At this time, if the Collector Emitter adds a positive voltage, under the action of the electric field, the electrons in the emission region will move to the base region (in fact, they all move in the opposite direction). Due to the small width of the base region, the electrons can easily cross the base region to the collector region and compound with the holes of the PN here (close to the collector). In order to maintain balance, Under the action of positive electric field, the electrons in the collector region accelerate the movement of the outer collector, while the holes move at the PN junction, which is similar to an avalanche process. The electrons from the collector return to the emitter through the power supply, which is the working principle of the transistor. When the triode works, the two PN junctions will induce charges. When the switch is in the on state, the triode is in the saturated state. If the triode stops at this time, the charges induced by the PN junction will return to the equilibrium state. This process takes time. MOS triodes work in different ways and do not have this recovery time, so they can be used as high-speed switches.
(1) The FET is a voltage control element and the transistor is a current control element. When only less current is allowed to be taken from the signal source, FET shall be selected; Under the condition that the signal voltage is low and more current is allowed to be taken from the signal source, transistors should be selected.
(2) MOSFETs conduct electricity by using most carriers, so they are called unipolar devices, while transistors conduct electricity by using both most carriers and a few carriers. It is called bipolar device.
(3) The source and drain of some FET can be used interchangeably, the gate voltage can be positive or negative, and the flexibility is better than that of transistor.
(4) FET can work under the condition of very small current and low voltage, and its manufacturing process can easily integrate many FET on a silicon wafer. Therefore, FET has been widely used in large-scale integrated circuits.
(5) Field effect transistor has the advantages of high input impedance and low noise, so it is also widely used in various electronic devices. In particular, using FET as the input stage of the whole electronic equipment can obtain the performance that is difficult to achieve by ordinary transistors.
(6) FET is divided into junction type and insulated grid type, and its control principle is the same.

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