The full bridge circuit is a circuit commonly used in DC motor control, which is composed of four MOS tubes, of which two MOS tubes are connected to the positive and negative terminals of the motor, and the other two MOS tubes are connected to the midpoint of the motor. By controlling the conduction and cutoff of four MOS tubes, the forward and reverse rotation and speed control of the motor can be realized.
The following is the principle of a full bridge circuit driven by 4 MOS tubes:
1. Working status
In the working state, two MOS tubes Q1 and Q4 are on, and two MOS tubes Q2 and Q3 are off. At this time, the positive electrode of the motor and the midpoint are connected together, the negative electrode and the midpoint are connected together, and the electric machine is turning positively.
2. Reverse the status
In the reversed state, two MOS tubes Q2 and Q3 are on, and two MOS tubes Q1 and Q4 are off. At this time, the negative electrode and the midpoint of the motor are connected together, the positive electrode is connected with the midpoint, and the electric machine is reversed.
3. Braking status
In the braking state, the four MOS tubes Q1, Q2, Q3 and Q4 are all cut off. At this time, both ends of the motor will be short-circuited, and the motor will be subjected to braking torque.
4. Brake status
In the braking state, two MOS tubes Q1 and Q3 are on, and two MOS tubes Q2 and Q4 are off. At this time, the positive and negative electrodes of the motor are connected together, and the motor brakes quickly to stop.
It should be noted that in order to control the on-off and off of the four MOS tubes, a specific control circuit needs to be used. The control circuit can adopt different control methods according to the need, such as PWM speed regulation, direct control, etc. At the same time, in order to protect the circuit and the motor, it is necessary to design the corresponding protection circuit, such as overcurrent protection, overvoltage protection and so on.
It can realize the positive and negative transformation of the voltage and current direction to achieve the purpose of controlling the positive reversal of the motor.
Its working principle is through the upper and lower two groups of mos tubes, respectively connected to the positive and negative terminals of the DC power supply, in the process of changing the mos tube switching state, the positive and negative voltage required by the motor is connected to both ends of the motor, so as to achieve the purpose of positive or reverse motor.
At this time, the frequency controlled by the mos tube switch should be higher than the motor operating frequency to avoid motor vibration or noise. In addition, the use of the full bridge circuit has another advantage is that the speed control can be achieved by adjusting the duty cycle.
The switching control circuit of four mos tubes is modulated into pwm signal, through the change of duty ratio, the efficiency and speed of the motor can be effectively controlled and adjusted, which is suitable for different work occasions and load conditions.
The principle of the full bridge circuit driven by 4 MOS tubes is as follows:
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A full-bridge circuit is a power conversion circuit that can convert direct current into alternating current, or change the frequency, voltage, or current of alternating current. It consists of four MOS tubes, divided into two groups of two MOS tubes each. Alternating conduction between each group of MOS tubes can produce a complete periodic AC signal.
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When the upper half bridge MOS tube is on, the lower half bridge MOS tube is disconnected, and the positive electrode of the power supply provides the power supply voltage to the upper half bridge MOS tube, while the negative electrode of the lower half bridge MOS tube reaches the site through the load. This allows the load to receive a positive half-cycle current signal.
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At the end of the positive half cycle, the upper half bridge MOS tube is disconnected and the lower half bridge MOS tube is switched on. At this time, the two ends of the load are connected to the negative power supply, thereby reversing the load electrode.
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Through this alternating on and off mode, an AC waveform with controllable frequency and working period can be generated at the load electrode, so as to realize the conversion from DC to AC.
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It should be noted that electromagnetic interference and noise will be generated at the moment of MOS tube switching, so a filter circuit needs to be added to suppress it.
A full-bridge circuit driven by four MOSFETs (metal oxide semiconductor field effect tubes), usually used for the control of loads such as DC Motor or Stepper Motor. Here's how it works:
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1. The full bridge circuit consists of four n-channel or P-channel MOSFETs, which use the switching characteristics of MOSFETs to control the forward and reverse rotation and speed of the DC motor or stepper motor.
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2. In the first half of the cycle, the M1 and M3 switches are on, and the M2 and M4 switches are off. At this time, the positive electrode of the DC power supply is connected to M1 and M3, while the negative electrode is connected to M2 and M4, and the current flows through the load or the motor.
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3. In the negative half cycle, the M2 and M4 switches are on, and the M1 and M3 switches are off. At this time, the positive electrode of the DC power supply is connected to M2 and M4, while the negative electrode is connected to M1 and M3, and the current flows through the load or the motor.
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4. The microcontroller or other logic unit controls the state of the switching circuit through PWM (pulse width modulation) signals, so as to achieve the purpose of controlling the direction and speed of the motor.
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5. In the process of switching MOSFET, because MOSFET has leakage induction Capacitance (Miller Capacitance) and internal resistance and other electrical characteristics, MOSFET switching may produce overshoot voltage and transient current, need to be through the external reset circuit, peak limiter and other measures to protect the circuit.
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In short, the use of four MOSFETs to build a full bridge circuit can achieve effective control of DC motor or stepper motor, but also involves the design and implementation of some protection circuits.