1. Working nature: The triode is controlled by current, and the MOS tube is controlled by voltage.

2. Cost issue: triodes are cheap and mos tubes are expensive.

3. Power consumption problem: the triode loss is large.

4. Driving ability: mos tubes are often used for power switches and high-current local switch circuits.

The triode is relatively cheap and easy to use, and is often used in digital circuit switch control.

MOS tubes are used in high-frequency high-speed circuits, high-current occasions, and places that are sensitive to base or drain control currents.

The MOS tube can not only be used as a switching circuit, but also can be used for analog amplification, because the change of the gate voltage within a certain range will cause the change of the on-resistance between the source and the drain.

The main difference between the two is that the bipolar tube is a current-controlled device (a larger collector current is controlled by a smaller current in the base), and the MOS tube is a voltage-controlled device (the on-resistance between the source and the drain is controlled by the gate voltage. ).

The on-voltage drop of the MOS tube (field effect tube) is low, the on-resistance is small, the gate drive does not need current, the loss is small, the driving circuit is simple, it has its own protection diode, and the thermal resistance characteristics are good, suitable for high-power parallel connection, shortcoming switching The speed is not high and it is more expensive.

The switching speed of the triode is high, and the Ic of the large triode can be made very large, but the disadvantage is that the loss is large, the base drive current is large, and the drive is complicated.

Generally speaking, in low-cost occasions, triodes are first considered for ordinary applications, and MOS tubes are considered if not possible.

In fact, it is wrong to say that the current control is slow and the voltage control is fast. To really understand it, 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 voltage-applied or not, the pn junction composed of the base region and the emitter region is to prevent multiples (the base region is the hole). , the emission region is the diffusion movement of electrons), at this pn junction, an electrostatic field (ie built-in electric field) from the emission region to the base region will be induced. When the positive voltage applied to the base is directed to the base region to the emission region, when When the electric field generated by the applied voltage to the base is greater than the built-in electric field, the carriers (electrons) in the base region may flow from the base region to the emitter region. The minimum value of this voltage is the forward conduction voltage of the pn junction (generally considered in engineering). 0.7v). But at this time, there will be charges on both sides of each pn junction. At this time, if a positive voltage is applied to the collector-emitter, under the action of the electric field, the electrons in the emitter region move to the base region (actually, the electrons move in the opposite direction). ), due to the small width of the base region, electrons can easily cross the base region to the collector region and recombine with the PN holes here (close to the collector). The electrons 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 go back to the emitter through the power supply, which is how a transistor works. When the triode is working, both pn junctions will induce charges. When the switch is in an on state, the triode is in a saturated state. If the triode is turned off at this time, the charge induced by the pn junction will return to a balanced state, which takes time. The mos triode works differently and does not have this recovery time, so it can be used as a high-speed switch.

(1) FETs are voltage-controlled elements, while transistors are current-controlled elements. In the case that only less current is allowed to be taken from the signal source, the FET should be selected; and in the condition that the signal voltage is low and more current is allowed to be taken from the signal source, the transistor should be selected.

(2) Field effect transistors use majority carriers for conduction, so they are called unipolar devices, while transistors have both majority carriers and minority carriers for conduction. are called bipolar devices.

(3) The source and drain of some FETs can be used interchangeably, and the gate voltage can also be positive or negative, which is more flexible than transistors.

(4) The field effect transistor can work under the condition of very small current and very low voltage, and its manufacturing process can easily integrate many field effect transistors on a silicon wafer, so the field effect transistor is widely used in large-scale integrated circuits. has been widely used.

(5) Field effect transistors have the advantages of high input impedance and low noise, so they are also widely used in various electronic devices. In particular, the use of field effect transistors as the input stage of the entire electronic device can achieve performance that is difficult to achieve with ordinary transistors.

(6) Field effect transistors are divided into two categories: junction type and insulated gate type, and their control principles are the same

Other comparisons:

1. The triode is a bipolar tube, that is, when the tube is working, two carriers, namely holes and free electrons, are involved.

 The field effect tube is a unipolar tube, that is, when the tube works, it either only has holes or only free electrons participate in conduction, and there is only one

 carrier

2. The triode is a current control device, and there is an input current to have an output current

  The field effect transistor is a voltage control device, and there is no input current and there will be an output current

3. The input impedance of the triode is small, and the input impedance of the FET is large.

4. The source and drain of some FETs can be interchanged, but the collector and emitter of triodes cannot be interchanged.

5. The frequency characteristics of the FET is not as good as that of the triode

6. The noise figure of the FET is small, which is suitable for the pre-stage of the low-noise amplifier

7. If you want the signal source current to be small, you should use a field effect transistor, otherwise it is more appropriate to use a triode