Principle of stepper motor driver system circuit based on AT89C2051

 
 Schematic diagram of stepper motor driver system circuit
　　AT89C2051 outputs control pulse from P1.4~P1.7 of P1 port, enters 9014 after inversion by 74LS14, controls photoelectric switch after amplification by 9014, and after photoelectric isolation, the pulse signal is amplified by power tube TIP122 for voltage and current amplification to drive each phase winding of the stepper motor. The stepper motor can perform forward, reverse, accelerate, decelerate and stop actions according to different pulse signals. L1 in the figure is a phase winding of the stepper motor. AT89C2051 uses a crystal oscillator with a frequency of 22MHz. The purpose of using a higher crystal oscillator is to minimize the influence of AT89C2051 on the pulse signal cycle of the host computer under mode 2.
    
　　RL1~RL4 in the figure are the internal resistance of the winding, and the 50Ω resistor is an external resistor, which plays a current limiting role and is also a component to improve the loop time constant. D1~D4 are freewheeling diodes, which attenuate the back electromotive force generated by the motor winding through the freewheeling diodes (D1~D4), thereby protecting the power tube TIP122 from damage.
    
　　A 200μF capacitor is connected in parallel with the 50Ω external resistor to improve the leading edge of the current pulse injected into the stepper motor winding and improve the high-frequency performance of the stepper motor. The 200Ω resistor connected in series with the freewheeling diode can reduce the discharge time constant of the loop, making the trailing edge of the current pulse in the winding steeper and the current falling time shorter, which also plays a role in improving the high-frequency working performance.