What Is a Motor Driver?
Motors need more current than a standard microcontroller can handle so we use drivers. These circuits are designed to accept power and a command from the next loop, the position or velocity loop.
These drivers interpret the pulse signals from the microcontroller and turn them into motor motion. To do this, they have transistors arranged in an H-bridge pattern.
Power
The motor driver is the critical link between the microcontroller and the actual actuation of the motors. Motor drivers take low-power signals from the microcontroller and step them up to the higher voltages, currents and pulse shapes required by the motors. They also regulate the voltage of the MOSFETs based on the motor operating conditions.
This is one of the most important factors to consider when selecting a driver for your application. The exact calculation is a bit complex and requires knowledge of the circuit design, PCB layout and lead inductance. It also depends on the driving condition of the motor and the power supply (voltage, current) of the driver IC.
Another factor is the power dissipation of the driver IC, which can be calculated from the peak drive current specified in the datasheet. The actual dissipation is a function of the driver IC bias current, MOSFET ON resistance and ambient temperature. TI’s driver ICs have OCP circuits that help protect the device from damage or degradation by limiting the peak drive current to a level safe for the silicon.
Finally, most motor driver ICs have thermal shutdown circuits that disable the outputs when the die temperature reaches a threshold value, protecting both the IC and the motors from damage or failure. This can be a useful safety feature, especially when the system uses high-power motors or has limited space for the driver IC.
Control
Motor drivers can control the speed, direction and torque of electric motors by converting a low-power signal from controller circuits like microcontrollers into the high current needed to drive a motor’s coils. This creates control that can’t be achieved with simple motor connections and increases the energy efficiency of the motors.
The heart of a motor driver is a pair of power transistors that act as switches for polarity and direction. A control system, such as a microcontroller, sends step and direction signals motor driver to the H-bridge power transistors which then activate and deactivate the appropriate motor coils. This controls the speed and direction of the motors and allows them to be controlled without any external wires.
Additionally, motor drivers may contain additional components for voltage regulation, PWM generation, braking, current sensing and protection. This can provide features not available with a standard controller chip that improve the quality of the output voltage, reduce waste and prevent damage to the motors.
Many motor drivers are integrated circuits (IC) designed specifically for a specific motor type like brushed DC or brushless DC motors. They often feature a special transistor configuration such as an H-bridge to manage the motor’s speed and direction while taking input signals from a higher level controller like a microcontroller or USB. Motor drivers with USB support can even be controlled directly from a computer or other USB-supported device.
Safety
The motor driver bridges the gap between digital commands and real-world power delivery. It takes low-level control signals, amplitudes them up to the proper voltage and current levels for the motor and then provides discrete outputs that translate those signals into proportional power delivery. It also includes components like current sensing, PWM generation, braking, and protection to ensure optimal performance.
It is important to match the motor driver and controller to the electrical specifications of your load. Small motors don’t require much current, and are usually run at lower voltages (less than 12V). Larger motors can draw high currents at startup and stall conditions, and will operate at higher voltages. Motor drivers and controllers should have the appropriate current and voltage ratings to avoid damaging them or your motors.
Many motor drivers are designed with built-in STO safety functions to enable a safe process stop in the event of an overload condition. This function ramps the motor speed down to a stop, fulfilling the requirements of Stop Category 1 per EN 60204-1.
Other features in some advanced driver ICs include built-in FMEDA, fault detection, over-temperature shutdown, and regeneration capabilities to reduce system cost and bldc driver simplify design. They can even incorporate CAN or SPI communication interfaces for more flexible connectivity to other devices in the system. This makes them easy to integrate into your application and meet the demands of ISO 26262 and IEC 61508 safety standards.
Applicability
A motor driver is an essential component in robotics systems, enabling the controller to easily and accurately control the position, speed and direction of a motor. It works by converting the constant voltage from an AC power source into variable current that can be used to operate motors.
A motor controller is the brains of a robot, and the driver is its brawn. They are distinct from each other, although some systems may blur the distinction between them. This can be true of centralized systems where the controller and motor drivers reside in the same cabinet or decentralized systems where the microcontrollers are co-located near the motors but communicate with them using a motion field bus.
The circuitry of a motor driver depends on the type of motor it is designed to drive. For example, a motor driver for DC or stepper motors can use H bridge circuitry to control the speed and direction of the motor. A motor driver for inductive loads such as relays, solenoids and transformer can use a simpler direction-controlling circuit.
When it comes to obtaining a motor driver’s license, New York state residents must take a written knowledge test and obtain proof of identity and residency. They also must pass a physical examination and meet minimum health requirements. Out-of-state residents may be eligible for a temporary license if they meet certain criteria. The license application fee is $100.
