**

Elaborate MOS Management knowledge -MOS Analysis, principle and difference of tube high-end drive and low-end drive

**
Detailed explanation MOS High end drive and low end drive of tube , Let's take a look at what is high-end drive 、 What is low-end drive .

High end drive ：
The principle of high-end power switch drive is very simple , Corresponding to low-end power switch drive , That is, one end of the load is connected to the switch tube , The other end is directly grounded . Under normal circumstances , When there is no control signal , The switch tube is not conductive , No current flows through the load , That is, the load is in the power-off state ;
conversely , If the control signal is valid , Turn on the switch tube , So the current flows from the positive end of the power supply through the high-end switch tube , Then it flows out through the load , The load enters the power on state , The act of producing a response . The basic driving schematic diagram is shown in the figure .

Generally, the switching power tube used now is N type MOSFET,N type MOSFET The utility model has the advantage that the driving adopts voltage driving , The driving current is very small , Low driving power consumption , And the working frequency can be very high , Suitable for high-speed control , in addition MOSFET The conduction internal resistance of is very low , At the milliohm level , The steady current that can pass through is very large , Therefore, it is suitable for high-power driving .P Type MOSFET Relative to the same silicon area , The internal resistance of conduction is large , The switching speed is also relatively slow , so N type MOSFET More use .

Low end drive ：
The principle of low-end power switch drive is very simple , That is, one end of the load is directly connected to the positive end of the power supply , The other end is directly connected with the switch tube , Under normal circumstances , When there is no control signal , The switch tube is not conductive , No current flows through the load , That is, the load is in the power-off state ; conversely , If the control signal is valid , Turn on the switch tube , So the current passes through the load from the positive end of the power supply , Then it flows out through the power switch , The load enters the power on state , The act of producing a response . The basic driving schematic diagram is shown in the figure .

Generally, the switching power tube used now is N type MOSFET,N type MOSFET The utility model has the advantage that the driving adopts voltage driving , The driving current is very small , Low driving power consumption , And the working frequency can be very high , Suitable for high-speed control , in addition MOSFET The conduction internal resistance of is very low , stay mΩ Level , The steady current that can pass through is very large , Therefore, it is suitable for high-power driving .P Type MOSFET Relative to the same silicon area , The internal resistance of conduction is large , so N Type is suitable for many .

The difference between high-end drive and low-end drive ：
High end drive refers to switching operation at the power supply end of the load , Low end drive refers to the switching operation at the grounding end of the load . The obvious difference is , If it's a low-end drive , Then one end of the load will always be connected to the power supply . There are many differences in application , But each has its own advantages and disadvantages , such as , If you want to do current sampling , Then differential sampling is required for low-end switch , The high-end switch can be sampled by one line . There are also some security considerations , such as , If your drive fails, it will cause safety problems , Obviously, high-end switches are safer .

High end drive refers to using high voltage to control the output relative to the working voltage of the load , The low-end drive refers to controlling the output with low voltage relative to the working voltage of the load .

Talking about MOS High end drive and low end drive of tube
Low end drive ：
MOS The tube is at the low end of the potential relative to the load , among D Connect the power supply through the load ,S Direct ground . about NMOS, Only when Vgs When it is greater than the opening voltage ,MOS The tube can conduct . So when it doesn't turn on ,S At an uncertain potential . If you let Vgs Greater than opening voltage , be DS Conduction ,S Determined as ground potential , At this time, we can still guarantee Vgs Greater than opening voltage , keep DS Conduction .

And for PMOS, Only to Vgs Less than a value ,MOS To turn on . here S At an uncertain potential . If you let Vgs Less than the opening voltage , Even if it turns on ,S Make sure it drops to ground potential , There is no guarantee that Vgs Less than the opening voltage .

High end drive ：
MOS The tube is at the high end of the potential relative to the load , among D Connect the power supply directly ,S Grounding through load . about NMOS, Only when Vgs When it is greater than the opening voltage ,MOS The tube can conduct . So when it doesn't turn on ,S At an uncertain potential . Even if you let Vgs Greater than opening voltage ,DS After conduction ,DS The potential is equal , Same as power supply potential , Unless G The pole potential is higher than the power potential , It cannot be kept on .

And for PMOS, Only to Vgs Less than a value ,MOS To turn on . here S At an uncertain potential . If you let Vgs Less than the opening voltage , send DS Conduction ,DS Same as power supply potential , Can still keep Vgs Less than the opening voltage , yes MOS Keep on .

It can be seen from the above that ,PMOS Suitable for high-end drive ,NMOS Suitable for low-end drive . However, due to various reasons such as technology . In case of high current , Usually still NMOS As a high-end driver . therefore , In order to ensure the high-end drive NMOS Of Vgs Keep above the opening voltage . We'll use half bridge driver chips . The half axle drive chip drives the high-end NMOS Of S Pole as a reference , Output a constant on voltage , To control MOS On of .