Easy to understand: basic knowledge of MOS tube

1、 Determination of three poles

G extremely (gate)— Grid , Needless to say, it's easier to recognize  S extremely (source)— Source pole , Whether it's P The ditch is still N Ditch , Where two lines intersect is  D extremely (drain)— Drain electrode , Whether it's P The ditch is still N Ditch , It's the side with separate leads

2、N Channel and P Channel discrimination

The arrow points to G The extreme is N Ditch   Arrow back G The extreme is P Ditch

3、 Parasitic diode direction determination

Regardless of N The ditch is still P Ditch MOS tube , The arrow direction of the intermediate substrate is always the same as that of the parasitic diode ：  Or all by S Point to D, Or both D Point to S

4、MOS The functions realized by the switch

1. Signal switching  

2. Voltage on-off

5、MOS Connection method in circuit when tube is used as switch

Key points ：

1. Make sure that pole is connected to the input , That pole is connected to the output  

2. NMOS The control pole level is high when MOS The pipe is open  

3. PMOS The control pole level is low   when MOS Pipe cut off  

NMOS：D Polar input ,S Polar output  PMOS：S Polar input ,D Polar output

Counter evidence strengthens understanding  NMOS If ：S Connect input ,D Connect output

 

Because the parasitic diode is directly on , therefore S The pole voltage can be reached unconditionally D extremely ,MOS The tube loses its function as a switch .

NMOS Characteristics of ,Vgs Greater than a certain value will turn on , Suitable for source grounding ( Low end drive ), As long as the grid voltage reaches a certain voltage （ Such as 4V or 10V,  Other voltages , Read the manual ） That's all right. .

 

PMOS If ：D Connect input ,S Connect output  

Also lost the function of the switch

PMOS Characteristics of ,Vgs Less than a certain value will turn on , Suitable for source grounding VCC The case when ( High end drive ). however , although PMOS It can be easily used as a high-end driver , But due to the high on resistance , Expensive price , Reasons such as few replacement types , In the high-end drive , Usually it's still used NMOS.

 

6、MOS Switching conditions of the tube

Above

7、 Relevant concepts

BJT ：Bipolar Junction Transistor Bipolar transistor ,BJT It's a current control device ; 

FET ：Field Effect Transistor Field effect transistor ,FET It's a voltage control device .

According to the structure, FET is divided into ： Junction field effect ( abbreviation JFET)、 Insulated gate field effect ( abbreviation MOSFET) Two categories: . According to channel material ： Junction type and insulating grid type N Channel and P Two kinds of ditches . In a conductive manner ： Depletion and enhancement , Junction FET are all depletion type , The insulated gate FET has both depletion type , There are also enhanced .  In general, field effect transistors can be divided into junction field effect transistors and MOS Field effect transistor , and MOS Field effect transistors are divided into N Channel depletion and enhancement ;P Channel depletion type and enhanced type .

8、MOS Tube important parameters

1. encapsulation  

2. type (NMOS、PMOS) 

3. Withstand pressure Vds( The maximum voltage that the drain and source can withstand when the device is disconnected ) 

4. Saturation current Id 

5. On impedance Rds 

6. gate threshold voltage Vgs(th)

9. from MOS Physical identification pin of pipe

Whether it's NMOS still PMOS  Align in the direction shown above , The middle foot is D, On the left for G, On the right is S.  Or remember ： A single foot is D, Turn counter clockwise DGS.  By the way, the pin identification of triode ： Also align in the direction shown above , The middle foot is C, On the left for B, On the right is E.

Pin number  

from G Foot start , Anti-clockwise 123  The pin number of triode is also from B Foot start , Anti-clockwise 123

10. Use a multimeter to identify NNOS、PMOS

Use parasitic diodes to identify . Turn the multimeter to diode , Red lead to S, Black pen to D, There is a numerical display , Conversely, there is no value , That is the N Ditch , If the opposite is true P Ditch .

 

11. NMOS/PMOS Generally used for switching circuits

NMOS It is generally used to control the conduction to the power end ：

PMOS It is generally used to control the conduction to the ground ：

12. Commonly used NMOS/PMOS- The switching frequency should be considered when selecting 、 Withstand pressure 、 Maximum current that can be passed

NMOS：  AO4484 SI2302 

PMOS：A04885 SI2301