How to choose a Motor Driver
Introduction:
How to Choose a Motor Driver- In robot projects, we use different types of motors, such as brushed motors, brushless motors, stepper motors, and servo motors. These motors can be controlled using different methods. Brushed motors and brushless motors can be directly driven by connecting them to an appropriate power source, while stepper motors and servo motors require a control signal to actuate. In this article, we will discuss, motor drivers for controlling the motors.
What is a motor drive circuit?
Introducing a motor drive circuit allows for the control of high current output using low current signals, thereby driving the motor. Typically, a motor drive circuit can be seen as an interface device between the motor and the control circuit, allowing you to control high current loads with low current signals. Additionally, it provides stable high voltage and high current for the project, enabling the motor to operate in an appropriate working state.
A motor drive circuit comprises IC controllers or discrete field-effect transistors capable of handling high-power electrical signals. It serves as a current amplifier circuit, acting as a bridge between the controller and the motor. Essentially, the drive circuit includes an H-bridge (to control the motor) and circuits controlling how the H-bridge operates. Different drive chips offer different interfaces. Some well-known motor drive circuits on the market include the L293D and L298N.
H-Bridge Circuit
The H-bridge (as shown in the diagram below) is a very simple circuit that can control the forward or reverse movement of a DC motor—in other words, this circuit can change the polarity of the voltage applied to the load.
When Q1 and Q4 are conducting, Vbat is connected to the left end of the motor, and GND is connected to the right end of the motor, causing the motor to move in one direction. When Q2 and Q3 are cut off, Vbat acts on the right end of the motor, and GND acts on the left end of the motor, causing the motor to move in the opposite direction.
An H-bridge can be easily made up of four transistors: two PNP and two NPN. Vcc switching is done using PNP transistors, and GND connection switching is done using NPN transistors.
Choosing a Motor Driver
So how do you choose the best motor driver for your project? Here are some important criteria to consider when selecting a motor driver:
Compatibility
When selecting a motor driver, the first thing to look for is the list of compatible motors for the motor driver. Most motor drivers can support brushless DC motors, geared motors, and stepper motors, and some motor drivers also support angle-controlled motors, such as servo motors. Therefore, you need to choose a driver based on your motor.
Interface
Most motor drivers are compatible with Arduino and other TTL inputs. However, if you want to control the motor wirelessly, such as using a Bluetooth control board, you may consider using a driver that supports remote controllers. In addition, the number of control channels must also be considered. When 16 external signals are needed to control 16 motors, and the current and voltage are met, then a motor driver that supports 16-channel control must be selected.
Voltage and Current
Next, look at the handling capability of voltage and current. Determine the voltage range of the motor driver based on the project requirements. Finding a suitable voltage range is not difficult. Motor drivers usually support a wide range of voltages (such as 4.5V – 36V). In addition, the current handling capability of the driver should also be noted.
On-State Resistance
In the motor driver chip, the resistance of the bridge transistor when the current passes through it is called the on-state resistance, which causes power loss. Power loss can be expressed as P = I^2R, where R is the on-state resistance and I is the current. Power loss results in heating. When the driver IC operates at peak current, the internal temperature increases rapidly, which may cause thermal protection shutdown. Therefore, you need to choose a control IC with sufficient current handling capability and add a physical heat sink. Often, there is not enough space on the motor control board PCB to add a heat sink, so we should choose an IC with low on-state resistance to achieve minimal power loss.
