Understanding Stepper Motor Controller
Stepper motor come in various sizes, versions, and operating voltages. This versatile controller offers a significant advantage as it can function effectively across a wide range of operating voltages, ranging from approximately 5 V to 18 V. It can propel the stepper motor with a peak voltage equal to half the supply voltage, making it suitable for stepper motors designed for voltages within the 2.5 V to 9 V range. Furthermore, the circuit is designed to deliver motor currents of up to 3.5 A, rendering it capable of driving relatively large motors.
Safety Features and Versatility
In addition to its versatility, the circuit boasts short-circuit protection and built-in overtemperature safeguards.
Control Signals for Stepper Motors
To drive a stepper motor, two essential signals are required. In logical terms, these signals form a Grey code, signifying two square-wave signals sharing the same frequency but with a consistent 90-degree phase difference. IC1 takes charge of generating a square-wave signal with an adjustable frequency, facilitated by potentiometer P1. This frequency plays a critical role in determining the revolutions per minute (rpm) of the stepper motor.
Generating the Grey Code
The Grey code is produced through a decimal counter represented by a 4017. As the clock signal experiences rising edges, the outputs Q0-Q9 of the counter sequentially go high. Subsequently, the Grey code is derived from these outputs by utilizing two OR gates. Each gate is constructed using two diodes and a resistor. These gates produce the ‘I’ (in-phase) and ‘Q’ (quadrature) signals, with the latter featuring a 90-degree phase offset from the ‘I’ signal.
H-Bridge Implementation for Stepper Motors
Typically, stepper motor windings are controlled using a pair of push-pull circuits for each winding. This configuration is known as an ‘H bridge.’
Reversing Current Direction for Bipolar Motors
To ensure proper operation of bipolar motors, the capability to reverse the current direction in each winding is essential. This feature is also useful for driving unipolar motors with center-tapped windings. In this context, we chose to employ audio amplifier ICs, specifically the TDA2030, despite its unconventional application. Functionally, the TDA2030 serves as a power opamp, featuring a difference amplifier at the input and a push-pull driver stage at the output.
Utilizing TDA2030 Amplifiers for Motor Control
IC3, IC4, and IC5, all of the TDA2030 type, are economically priced and play crucial roles in the system. IC3 and IC4 function as comparators with their non-inverting inputs driven by the I and Q signals. While the inverting inputs are set to a potential equal to half the supply voltage, provided by the third TDA2030. The outputs of IC3 and IC4 track their non-inverting inputs and drive individual motor windings. The other winding ends connect to half the supply voltage, sourced from IC5.
Achieving Desired Bipolar Motor Control
By applying a square-wave signal alternated between 0 V and a potential close to the supply voltage to one end of each winding, while the other end remains at half the supply voltage, the winding always receives a voltage equal to half the supply voltage. This voltage alternates in polarity according to the states of the I and Q signals, making it suitable for driving a bipolar stepper motor. The motor’s speed, measured in revolutions per minute (rpm), can be adjusted using potentiometer P1. However, the actual speed varies depending on the motor type due to the number of steps per revolution.
Fine-Tuning Speed and Avoiding Startup Confusion
In principle, adjusting the value of capacitor C1 allows for attaining any desired speed, within the motor’s capacity. The adjustment range of potentiometer P1 can be extended by reducing the value of resistor R5. Specifically, the adjustment range is given by 1:(1000 + R5)/R5, with R5 represented in kΩ. Stepper motors may exhibit continued rotation due to inertia or mechanical loads even when the supply voltage is removed, potentially leading to discrepancies in motor position when power is reapplied.
Enhancing Motor Control and Preventing Confusion
To mitigate these issues, the addition of an optional switch, S1, and a 1-kΩ resistor is recommended to facilitate motor start and stop control. When S1 is closed, the clock signal halts while IC2 maintains its output levels, resulting in continuous currents through the motor windings that magnetically lock the rotor in place.
Thermal Management for High-Power Motors
For applications involving relatively high-power motors. It is advisable to mount IC3, IC4, and IC5 on a heat sink, possibly a shared one. The TO220 case’s tab is electrically connected to the negative supply voltage pin, allowing ICs to be attached to a shared heat sink without requiring insulating washers. This step helps prevent overtemperature issues. As the TDA2030 IC incorporates internal overtemperature protection, reducing the output current if it becomes excessively hot.