Wuxi Sanda Motor Technology Co., Ltd. would like to introduce the working principle and indicators of the speed control motor to you
The speed-regulated DC motor drive circuit should first consider the following performance objectives:
1. Output current and voltage scale. It depends on how much power the circuit can drive on the motor.
2. Power. High power not only means saving power, but also reduces the heating of the drive circuit. To improve the power of the circuit, we can start by ensuring the switching status of the power device and avoiding common conduction (a problem that may occur in the H-bridge circuit, that is, two power devices are turned on at the same time to short-circuit the power supply);
3. The impact on the power supply. Common state conduction can cause an instantaneous drop in power supply voltage to form high-frequency power supply pollution, and high current may cause the potential of the ground wire not stable;
4. Reliability. The motor drive circuit should do as much as possible: no matter what kind of control signal or loading has been added, the circuit is safe.
Through long-term experiments, the author obtained a speed-adjustable bidirectional DC motor drive circuit, the circuit is shown in the attached figure.
Input and battery conversion section
The input signal line is introduced by Port, Port 1 pin is the motor direction signal input end, Port 2 pin is the PWM signal input end, and Port 3 pin is the ground wire. Note that Port3 pin is connected to a 2kΩ resistor to ground. When the driver board and the microcontroller are powered separately, this resistor can provide a return path for the signal current. When the driver board and the microcontroller share a power supply, this resistance can prevent large current from flowing into the ground wire of the microcontroller motherboard along the connection line to cause interference. In other words, it is equivalent to separating the ground wire of the driver board from the ground wire of the single-chip microcomputer to realize "one-point grounding". Capacitor C1 prevents the motor from suddenly starting to cause a sudden drop in voltage.
The NAND gate U1A completes the modulation of the PWM signal and the motor direction signal, and converts it into a square wave signal close to the amplitude of the power supply voltage.
Transistor drive section
The circuit drive composed of triode, resistor and diode completes the adjustable speed forward and reverse drive of the DC motor. The four diodes function to protect the triode, avoiding the impact of the negative induced electromotive force generated by the rational component (motor) on the triode.
When the output terminal of 74LS00 is low level, Q2 and Q4 are cut off, Q1 and Q3 are turned on, and the output is high level. When the output terminal of 74LS00 is high level, Q2 and Q4 are turned on, Q1 and Q3 are cut off, and the output is low level.
The power supply voltage is 15-30v, and the continuous output current is 500mA/each motor, which can reach 700mA in a short time (10 seconds), and the PWM frequency can be used at 30kHz (generally 1-10kHz).