Principle and application of the most complete H-bridge motor drive module L298N

H Bridge - Basic knowledge of

Usually ,H A bridge is a fairly simple circuit , Contains four switching elements , The load is in the center , A similar H Configuration of .

Switching element (Q1…Q4) Usually bipolar or FET The transistor , For some high voltage applications IGBT. There are also integrated solutions , However, whether the switching element is integrated with its control circuit is irrelevant to most of this discussion . diode (D1…D4) It is called clamp diode , Usually Schottky type .

The top of the bridge is connected to the power supply （ For example, batteries ）, The bottom end is grounded .

Generally speaking , All four switching elements can be opened and closed independently , Despite some obvious limitations .

Although theoretically the load can be anything you want , But so far , If H The bridge has a brush DC or bipolar stepping motor （ Stepper motors each motor requires two H Bridge ） load , Is the most common application . In the following , I will focus on the application as a brush DC motor driver .

H Static operation of the bridge

H The basic working mode of the bridge is quite simple ： If Q1 and Q4 Conduction , The left lead of the motor will be connected to the power supply , The right lead is connected to the ground . The current begins to flow through the motor , Motor forward （ For example ） Electrify , The motor shaft starts to rotate .

If Q2 and Q3 Connect , Will be reversed , The motor is energized in reverse , The shaft will begin to rotate in the opposite direction .

In the bridge , You should never close at the same time Q1 and Q2（ or Q3 and Q4）. If you do , You're just in power and GND Creates a very low resistance path between , Effectively shorting your power supply . This situation is called “ breakdown ”, It is almost guaranteed to quickly destroy your bridge or other things in the circuit .

Due to the limitation of the four possible states ,A There are probably only three side switches that make sense ：

Q1	Q2
open	open
close	open
open	close

For the same B Noodles ：

Q3	Q4
open	open
close	open
open	close

Therefore, the whole bridge can have 9 Different states ：

Q1	Q2	Q3	Q4
close	open	open	open
close	open	open	close
close	open	close	open
open	close	open	open
open	close	open	close
open	close	close	open
open	open	open	open
open	open	open	close
open	open	close	open

There are also some combination patterns , No power supply to the motor . For example, when all four crystal switches are off , At this time, the motor load is equivalent to the suspension at both ends . If the motor is moving at this time , The kinetic energy of its rotor will be gradually consumed under the action of friction , The motor stops slowly .

The two cases shown in the figure below ：H The upper half of the bridge circuit （ Or the lower half ） The two transistors of the are closed , The other two corresponding transistors are off . At this time, both ends of the motor are actually short circuited by the bridge circuit . The voltage at both ends of the motor is 0. If the motor is moving at this time , Then the kinetic energy of its rotor will pass through the generated reverse electromotive force （EMF） The braking current is formed in the circuit loop of the external short-circuit bridge , The motor will brake quickly .

The short circuit of the same bridge arm is sometimes caused by poor control signal （ Didn't give enough dead time ）, Sometimes power devices are not strong enough （ The withstand voltage is not enough to be broken down ）. But because it concerns H The life and death of bridge circuit , So we need to avoid .

H- Bridge control motor

Take controlling a DC motor as an example , Yes H Several switch states of the bridge are briefly introduced , Among them, forward and reverse rotation are the artificial directions , In the actual project, it can be divided according to the actual situation .

Motor forward rotation control

Usually H Bridges are used to drive inductive loads , Here we drive a DC motor ;

Q1	Q2	Q3	Q4
open	close	close	open

Assume that the motor is rotating forward , This current goes through in turn Q1 , M , Q4 , Use yellow line segments to mark in the diagram , The details are shown in the following figure ：

Motor reverse control

Another state is that the motor reverses ; At this time, the status of the four switch components is as follows ;

Q1	Q2	Q3	Q4
close	open	open	close

At this time, the motor reverses （ Contrary to the situation described earlier ）, This current goes through in turn Q2 , M , Q3 , Use yellow line segments to mark in the diagram , The details are shown in the following figure ：

Motor speed regulation

If you want to speed the DC motor , One of the solutions is ;

close Q2 , Q3 ;

open Q1 , Q4 Enter it on the computer 50% Duty cycle PWM wave form ;

In this way, the effect of reducing the speed is achieved , If you need to increase the speed , Will enter PWM The duty cycle of is set to 100%; The details are as follows

Motor stop

Take the motor switching from forward to stop as an example , In forward rotation ; Q1 and Q4 It's on ;

At this time, if it's closed Q1 and Q4 , The equivalent inductance can be generated inside the DC motor , That's the perceptual load , The current doesn't jump , Then the current will continue to flow in the same direction , At this time, we hope that the current in the motor can quickly decay , There are two ways ：

The first one is ： close Q1 and Q4 , At this time, the current will still flow through the reverse freewheeling diode , It turns on briefly Q1 and Q3 So as to achieve the purpose of rapid attenuation of current .

The second kind ： Ready to stop , close Q1 , open Q2, The current doesn't decay very fast at this time , The current circulates in Q2,M,Q4 Flow between , adopt MOS-FET Consume the energy of internal resistance .

H- Bridge application

In practice , Made of discrete components H Bridges are troublesome , There are many commonly used ones on the market IC programme , For example, common L293D、L298N、TA7257P、SN754410 etc. . Connect the power supply 、 The motor , The motor can be driven by inputting the control signal .

The following is on a treasure L298N modular , More common , Very friendly to novice players , The wiring is also very simple .

L298N Module this module has an onboard 5V pressure regulator , The regulator can be enabled by jumper .

If the motor supply voltage is as high as 12V, We can enable 5V pressure regulator , also 5V Pins can be used as outputs , For example, to Arduino Board power supply .

however , If the motor voltage is greater than 12V, The jumper must be disconnected , Because these voltages can damage the onboard 5V pressure regulator .

under these circumstances ,5V The pins will be used as inputs , Because we need to connect it to 5V Power Supply , In order to make IC Normal work .

We can notice here , The IC The voltage drop is about 2V. therefore , If you use 12V Power Supply , The voltage at the motor terminals is about 10V, That means we won't be able to get from 12V Get the maximum speed in a DC motor .

Use here Arduino For example , This is one from the Internet Demo The overall framework is shown in the figure below ：

Main code

#define enA 9
#define in1 6
#define in2 7
#define button 4
 
int rotDirection = 0;
int pressed = false;
 
void setup() {
    
  pinMode(enA, OUTPUT);
  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
  pinMode(button, INPUT);
  // Set initial rotation direction
  digitalWrite(in1, LOW);
  digitalWrite(in2, HIGH);
}
 
void loop() {
    
  // Read potentiometer value
  int potValue = analogRead(A0); 
  // Map the potentiometer value from 0 to 255
  int pwmOutput = map(potValue, 0, 1023, 0 , 255); 
  // Send PWM signal to L298N Enable pin
  analogWrite(enA, pwmOutput); 
 
  // Read button - Debounce
  if (digitalRead(button) == true) {
    
  pressed = !pressed;
  }
  while (digitalRead(button) == true);
  delay(20);
 
  // If button is pressed - change rotation direction
  if (pressed == true  & rotDirection == 0) {
    
    digitalWrite(in1, HIGH);
    digitalWrite(in2, LOW);
    rotDirection = 1;
    delay(20);
  }
  // If button is pressed - change rotation direction
  if (pressed == false & rotDirection == 1) {
    
    digitalWrite(in1, LOW);
    digitalWrite(in2, HIGH);
    rotDirection = 0;
    delay(20);
  }
}

Code explanation

Briefly describe ： First of all, we need to define the pins and variables needed by the program .

stay setup() in , We need to set the pin mode and the initial rotation direction of the motor .

stay loop() in , Let's read the potentiometer first , Then take the value from 0 To 1023 change , Linear mapping to PWM The signal 0 To 255 Value , From the 0 To 100％ Duty cycle of .

And then use analogWrite() Function will PWM The signal is sent to L298N Board Enable Pin , This pin actually drives the motor .

Next , We check to see if the button is pressed , If so , We're going to enter 1 And the input 2 The state of is reversed , So as to change the direction of rotation of the motor . This button will be used as a toggle button , Each time the button is pressed, the direction of rotation of the motor is changed .

There are many such cars on a treasure , As shown in the figure below ; The master control can be replaced by 51 Single chip or STM32, Of course Arduino Also no problem , Use L298N You can quickly build a car ;

summary

Although we cannot confirm all the conclusions of the original author 、 The formulas are all correct . But seeing his clear words 、 Vivid illustrations 、 The detailed formula analysis reflects his need to design a small motor H The bridge circuit drives the project , I kept thinking about the principle of each link of the bridge circuit and some control details , And finally summarized into a blog . You can feel his inner joy in the whole process of knowledge growth .

Reference material

• H-Bridges – the Basics | Modular Circuits
• https://blog.csdn.net/tiandiren111/article/details/112130898

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