Experience of constructing H-bridge with MOS tube

Preface

Because I've been working on the driving circuit of smart car recently , Forward and reverse rotation shall be realized according to the requirements of the motor , So I think of... In the book H Bridge circuit , Of course, there are many integrated h Bridge chip ：LN298N etc. . I thought it would be more convenient to control when making a balance car, so I wanted to pick up a cheap one to use LN298N. But why don't teams use this integrated module as the driving circuit on the Internet ？… When I think about it, it's not so simple , So I checked LN298N The parameters of the chip and the parameters of the motor , good heavens , Almost fell into the pit (*>﹏<*)′(>﹏<)′`(>﹏<)′.....



　　 obviously L298N The module is not suitable for this design , Don't panic , Ask Du Niang first. It can really avoid some “ tragedy ”
No, then we'll use mos The tube builds a H Bridge circuit .....
Share a big man's summary

One place in the picture is curious , Why don't we all use N-MOS What about it ？ Why do we need to use P-MOS tube , And below N-MOS tube ？ Originally built H Bridge circuit also has a little trick ：
understand MOS The opening of the tube / Turn off the principle you will find , Use PMOS Do the pipe 、NMOS It's more convenient to run the pipe . Use PMOS Take care of it 、NMOS The circuit design of the upper tube is complex , In general, it doesn't mean much , So we seldom use .
Let's learn about MOS The opening of the tube / Shut off principle , Please look at the chart below. ：

　　NMOS The current direction of the main circuit of the tube is D→S, The conduction condition is VGS There is a certain pressure difference , It's usually 5_{10V（G Potential ratio S High potential ）; and PMOS The current direction of the main circuit of the tube is S→D, The conduction condition is VGS There is a certain pressure difference , It's usually -5}-10V（S Potential ratio G High potential ）, Let's turn on the differential pressure 6V For example
NMOS tube
　　 Use NMOS Inferior canal ,S Directly grounded （ Is a fixed value ）, Just put the G Fixed value of pole voltage 6V It can be connected ;
　　 If you use NMOS When you are in charge ,D Connect the positive power supply , and S The voltage of the pole is not fixed , Unable to determine control NMOS Open up G Pole voltage , because S There are two states of pole to ground voltage ,MOS When the tube is cut off, it is low level , Close to high level when conducting VCC.
　　 Of course NMOS It can also be a tube , It 's just that the control circuit is complicated , In this case, isolated power control must be used , Use one PMOS Things that can be solved are not usually done like this , Obviously increase the difficulty of circuit .

PMOS tube
　　 Use PMOS When you are in charge ,S The pole is directly connected to the power supply VCC,
　　 S The pole voltage is fixed , just G Pole voltage ratio S Very low 6V It can be connected , Easy to use ;
　　 Similarly, if you use PMOS Inferior canal ,D Pole grounded ,S The voltage of the pole is not fixed （0V or VCC）, It's impossible to determine the control pole G The voltage of the pole , Difficult to use , Isolation voltage design is required

summary :
　　 According to the conduction conditions of the two pipes , utilize S The combination of pole and power supply or ground can skillfully realize the conduction condition of the pipe ：
N-MOS ———— S Pole grounded
P-MOS ———— S Polar power supply

H Improvement of bridge circuit
Enable control and direction logic
　　 When driving the motor , Guarantee H It is very important that the two triodes on the same side of the bridge will not conduct at the same time . If the triode Q1 and Q2 Turn on at the same time , Then the current will pass from the positive pole through two triodes and return directly to the negative pole . here , There is no other load in the circuit except the triode , Therefore, the current on the circuit may reach the maximum value （ This current is limited only by the power supply performance ）, Even burn out the triode . For the above reasons , In practice, the driving circuit usually uses hardware circuit to easily control the switch of triode .
　　 Improving the circuit is fundamental H On the basis of the bridge circuit 4 A and gate and 2 A non gate .4 One is the same as the door “ Can make ” Connect the conduction signal , such , With this signal, the switch of the whole circuit can be controlled . and 2 A non gate provides a way to enter , It can be guaranteed that at any time H On the same leg of the bridge, only a triode can conduct .（ Same as the previous diagram in this section , chart 4 It is not a complete circuit diagram , In particular, the direct connection with the gate and triode in the figure can not work normally ）

We can use an isolation chip to realize enable control and direction logic control according to this idea
ENABLE = 1 DIR-L = 0 DIR-H = 1 The motor rotates forward as shown in the figure
ENABLE = 1 DIR-L = 1 DIR-H = 0 The motor is reversed as shown in the figure
In order to achieve the above functions, we can use a NAND gate column, such as ：74hc00
As shown in the figure, the motor rotates forward ：

The motor reverses ：

The advantage of this control lies in the up and down of the same bridge arm mos The tube will never be connected at the same time , Then it will not form a loop and cause the harm of short circuit

Use of diodes
Generally in mos When using, in order to prevent mos Breakdown by counter current , A freewheeling diode needs to be connected in parallel , Prevent reverse breakdown of FET , But there are many kinds of diodes , What kind of diode should we use ？ The difference between diodes

Characteristics of fast recovery diode and Schottky diode
1、 The reverse recovery time of fast recovery diode is hundreds of nanoseconds , And the Schottky diode is faster than it , Even a few nanoseconds ;

2、 The reverse breakdown voltage of fast recovery diode is high , Generally higher than 200V, Even thousands of volts , The reverse breakdown voltage of Schottky diode is very low , Common in 100 following , Some will be higher ;

3、 The power consumption of fast recovery diode is large , The reverse recovery time of Schottky diode is short 、 Low loss 、 Low noise