What is the difference between the triode and the MOS tube when doing the switch in circuit design?
  1. Transistor with current control, MOS tube belongs to voltage control.
  2, cost problem: transistor cheap, MOS tube expensive.
  3, power consumption problem: triode loss.

  4, driving capacity: MOS tube is commonly used for power switch, and large current local switching circuit.

In fact, the transistor is relatively cheap, easy to use, commonly used in digital circuit switch control.
MOS tubes are used in high frequency high-speed circuits, high current situations, and where base or drain control current is more sensitive.
In general, low cost occasions, common applications should first consider using triode, if not consider MOS tube
    In fact, it is not correct to say that current control is slow and voltage control is fast. You really need to understand how bipolar and MOS transistors work. The transistor works by the movement of the carrier. Take the npn tube emitter follower as an example, when the base is not voltage added, the pn composed of the base region and the emission region will prevent the diffusion movement of the multiple sons (the base region is a hole, the emission region is an electron), and the electrostatic field (that is, the built-in electric field) will be induced at the pn junction from the emission region to the base region. When the direction of the applied positive voltage of the base is the direction of the base region to the emission region, when the electric field generated by the applied voltage of the base region is greater than the built-in electric field, the carrier (electron) of the base region may flow from the base region to the emission region, and the minimum value of this voltage is the positive conduction voltage of the pn junction (generally considered 0.7v in engineering). However, at this time, there will be charges on both sides of each pn junction. At this time, if a positive voltage is added between the collector and emitter, under the action of the electric field, the electrons in the emission region will move towards the base region (in fact, the electrons will move in the opposite direction). Due to the small width of the base region, the electrons will easily cross the base region to the collector region and recombine with the holes of PN here (near the collector). In order to maintain the equilibrium, the electrons in the collector region accelerate the movement of the outer collector under the action of positive electric field, while the holes move at the pn junction, which is similar to an avalanche process. Electrons from the collector pass through the power supply back to the emitter, which is how transistors work. When the transistor is working, the two pn junctions will induce charge, when the switching tube is in the on-state, the transistor is in a saturated state, if the transistor is intercepted at this time, the charge induced by the pn junction should be restored to the equilibrium state, this process takes time. The MOS triode works differently and does not have this recovery time, so it can be used as a high-speed switching tube.
  (1) The field effect tube is a voltage control element, and the transistor is a current control element. When only a small amount of current is allowed from the signal source, the effect tube should be selected; When the signal voltage is low and more current is allowed from the signal source, the transistor should be selected.
  (2) The field effect tube uses a majority of carriers to conduct electricity, so it is called a unipolar device, and the transistor has a majority of carriers and also uses a minority of carriers to conduct electricity. It is called a bipolar device.
  (3) The source and drain of some Fets can be used interchangeably, and the gate voltage can also be positive or negative, which is better flexibility than the transistor.
  (4) Fets can work under very small current and very low voltage conditions, and its manufacturing process can easily integrate many fets on a silicon chip, so fets have been widely used in large-scale integrated circuits.
  (5) FET has the advantages of high input impedance and low noise, so it is also widely used in various electronic devices. In particular, the efficiency tube is used as the input stage of the entire electronic device, which can obtain performance that is difficult to achieve with ordinary transistors.
  (6) Fets are divided into two categories: junction type and insulated gate type, and their control principles are the same.