What is H bridge?
The H-bridge is a relatively simple circuit, which usually contains four independently controlled switching metaders (e.g., MOS-FETs), which are often used to drive current larger loads, such as motors, and why is it called H Bridge (H -Bridge), because of the specific letter h, as shown in the figure below;
There are four switching metaders Q1, Q2, Q3, Q4, and there is also a DC motor M, D1, D2, D3, D4 is the renewal diode of MOS-FET;
switch status
Below to control a DC motor as an example, a simple introduction of several switching status of the H-bridge, where the forward turn and reversal are the direction of human specified, and the actual work is divided according to the actual situation;
Forward
Usually the H-bridge is used to drive the sensitive load, where we drive a DC motor;
● Open Q1 and Q4;
● Turn off Q2 and Q3;
At this point, it is assumed that the motor is forwarded, this current is sequentially passed through Q1, M, Q4, and the yellow line segment is used in the figure, as shown in the figure below;
Another state is the motor reversal; at this time, the state of the four switching metaders is as follows;
● Turn off Q1 and Q4;
● Open Q2 and Q3;
At this time, the motor reverses (contrary to the situation described above), this current is sequentially passed through Q2, M, Q3, and labeled the yellow line segment in the figure, as shown in the figure below;
Reverse
Speed up
If you want to speed up the DC motor, one of the options is;
● Turn off Q2, Q3;
● Open Q1, Q4, input 50% PWM waveform of 50% duty cycle, which reaches the effect of reducing the speed. If you need to increase the speed, the duty cycle of the input PWM is set to 100%;
Specifically, as shown below;
Stop state
Here, the motor is switched from the forward switch to the stop state;
● Under normal transformation; Q1 and Q4 are open state;
● At this time, if Q1 and Q4 are turned off, the DC motor can be applied to inductive inductance, that is, inductive load, current does not mutation, then current will continue to keep the original direction, then we want the current in the motor to quickly attenuate ;
There are two ways here:
The first: Turn off Q1 and Q4, at this time, the current will still flow through the reverse continuation of the diode, and then open Q1 and Q3 to achieve the purpose of rapid attenuation current;
Second: When preparing to stop, turn off Q1, open Q2, at this time, the current does not attenuate quickly, the current cycle flows between Q2, M, Q4, and consumes electric energy through the internal resistance of MOS-FET;
application
When actually use, it is very troublesome to make an H bridge with discrete components. There are many commonly used IC schemes, such as commonly used L293D, L298N, TA7257P, SN754410, and the like. Connect the power supply, the motor, can drive the motor by entering the control signal;
Here is the L298N module on a treasure, is more common, very friendly for novice players, and it is also very simple;
L298N module
This module has a plate 5V regulator that can be enabled using jumpers.
If the motor power supply voltage is up to 12V, we can enable 5V regulator, and 5V pin can be used as an output, such as powering the Arduino board.
However, if the motor voltage is greater than 12V, the jumper must be disconnected because these voltages will damage the onboard 5V regulator.
In this case, the 5V pin will be used as an input because we need to connect it to the 5V power supply to make the IC work normally.
We can notice that the voltage of the IC is about 2V. Therefore, if the 12V power supply is used, the voltage on the motor terminal is about 10V, which means that we will not get the maximum speed from the 12V DC motor.
Here, Arduino is used as an example, which is the framework of a DEMO on the Internet is shown below;
Architecture
#define ENA 9
#define in16
#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 =! press;
}
While (DigitalRead (Button) == TRUE
DELAY (20);
// if button ispese - change rotation direction
IF (PRESSED == True & Rotdirection == 0) {
DigitalWrite (In1, HIGH);
DigitalWrite (IN2, LOW);
Rotdirection = 1;
DELAY (20);
}
// if button ispese - change rotation direction
IF (PRESSED == false & ratdirection == 1) {
DigitalWrite (In1, Low);
DigitalWrite (IN2, HIGH);
RotDirection = 0;
DELAY (20);
}
}
Simply description: First we need to define the pins and variables required for the program.
In Setup (), we need to set the pin mode and the initial rotation direction of the motor.
In LOOP (), let's read the potentiometer value, then change the value from 0 to 1023, linearly map 0 to 255 of the PWM signal, from 0 to 100% duty cycle.
Then use the analogwrite () function to send the PWM signal to the Enable pin of the L298N board, which actually drives the motor.
Next, we check if the button is pressed. If so, we will refer the state of input 1 and the input 2 to change the direction of rotation of the motor. The button will be used as a switch button, and each time the button will change the direction of rotation of the motor.
There are many trolles on a treasure, as shown below; the main control can be replaced with 51 single-chip or STM32, of course, Arduino is no problem, using L298N to quickly build a car;
A baby's car
Summarize
This paper briefly introduces the principle of the H-bridge, and simply introduces the state of the drive as an example, the overall relatively simple, suitable for novice players, and finally gives an example based on Arduino and L298N, for reference only.
Edit: hfy, read full text
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