A stepper motor is an open-loop controlled motor that converts electrical pulse signals into angular or linear displacement; it is also known as a pulse motor. Under non-overload conditions, the motor's speed and stopping position depend only on the frequency and number of pulse signals, and are unaffected by load changes. When a stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in a set direction, called the "step angle." The stepper motor rotates step by step at fixed angles. The angular displacement can be controlled by controlling the number of pulses, thus achieving accurate positioning. Simultaneously, the speed and acceleration of the motor can be controlled by controlling the pulse frequency, thus achieving speed regulation. Stepper motors are widely used in peripherals of digital computers, as well as printers, plotters, and disk drives.
There are three types of motor driver chips: 1. TMC5160 and L6474: These are relatively advanced drivers. The MCU directly sends commands to the driver chip via SPI/UART to drive and control the motor. 2. TB6600 and L6208: These drive the motor via pulses, specifically two types of pulses: one for speed and one for direction. The pulses that directly drive the motor are decoded by the chip. 3. The low-level ULN2003: This acts as an amplifier, enhancing the driving capability of the input pulses before connecting it to the stepper motor. It turns out that the ULN2003 is not actually a motor driver; the L6205 and A4954 are dedicated motor driver chips. They amplify the input before providing the output to the motor.
Stepper motors cannot be directly connected to AC or DC power supplies; they must be driven by a dedicated stepper motor driver, which consists of a pulse generation and control unit, a power drive unit, and a protection unit. The drive unit is directly coupled to the stepper motor and can be understood as the power interface of the stepper motor's microcontroller. The MCU is essentially the brain of the motor, sending parameters such as step angle, rotation direction, and number of repetitions to the discrete components. The discrete components, based on the signals from the MCU, amplify the voltage and current and send them to the motor, thereby driving the motor to rotate.
A brushed motor driver consists of an H-bridge core circuit and some necessary peripheral circuits. Integrated circuit H-bridges are generally used for low to medium power applications. Discrete component H-bridges are typically used for high or ultra-high power applications and are mainly composed of MOSFETs or IGBT transistors. MCU pins cannot directly drive MOSFETs and other components; a dedicated MOSFET driver chip is required. The L298N brushed DC motor driver chip integrates two H-bridges. The L298N chip can drive motors with a voltage of 4.5V to 46V and an output current of up to 2A, with a peak current output of up to 3A. In practical applications, where forward and reverse rotation cannot be achieved by swapping power lines, a single H-bridge circuit can be used to drive the motor.
The various advantages of microstepping drive circuits have led to their expanding application range. Currently, most microstepping drive circuits for stepper motors utilize single-chip microcomputer control. Based on the operating state of the final stage power amplifier transistor, microstepping drive circuits can be classified into two types: amplification type and switching type. In amplification type microstepping drive circuits, the output current of the final stage power amplifier transistor is directly controlled by the control voltage output by the microcontroller. Therefore, the circuit is relatively simple and has relatively strong current control capability. However, the final stage power amplifier transistor is in an amplification state for a long time, which greatly increases power consumption and causes severe heat generation, leading to excessively high circuit temperatures and potential accidents such as transistor temperature drift or thermal breakdown, thus affecting the normal operation of the entire circuit. Therefore, amplification type microstepping drive circuits are generally used in applications requiring low drive current, high control precision, and excellent heat dissipation. In a switching microstepping driver circuit, the final stage power amplifier transistor operates in a switching state, which greatly reduces power consumption and avoids the severe overheating issues associated with amplifying microstepping driver circuits. However, switching microstepping driver circuits are very complex and have a certain ripple in the output current. Therefore, switching microstepping driver circuits are generally used in stepper motor drives with extremely high output torque.
