DC motors – driver for motion of an autonomous robot
This article describes one possible solution for a DC motor driver for motion of an autonomous robot. An autonomous robot was designed for EUROBOT competition. System for motion consists of two DC motor drivers, one per wheel. Each driver is controlled by one motor controller. The main controller controls motor controllers. More about module for motion of an autonomous robot you can find in our previous article “DC motors – module for motion of autonomous“. A DC motor driver consists of a current limiter, control logic, delay circuit, MOSFETs switching circuit and H-bridge.
Basic units of a DC motor driver
A DC motor driver block for motion of an autonomous robot is displayed in the Image 1.
Image 1. DC motor driver block diagram
A schematic circuit of a DC motor driver consists of:
1. Current limiter circuit,
2. Control logic circuit,
3. Delay circuit (RC circuit),
4. MOSFETs switching circuit and
5. H-bridge circuit.
The DC motor driver control signals from Microchip, Arduino, Raspberry Pi, MikroElektronika…
The DC motor driver receives three control signals:
1. PWM (Pulse Width Modulation),
2. Direction and
sent by the motor controller (see Image 3 from the tutorial “DC motors – module for motion of autonomous”). The control logic circuit generates signals for switching on and of the MOSFETs. Some signals are additionally delayed by the delay circuit. The main part of the MOSFET switching circuit are two ICs (Integrated Circuit) IR2112. These components create signals for switching the lower and upper transistors in the H-bridge.
In our example those 3 input signals are generated by Atmel/Microchip AT89S8252 MCU but also can be generated by popular platforms as Arduino, Raspberry Pi, MikroElektronika Hardware and Software Embedded Tools…
A delay circuit or an RC circuit
Delay circuit is a RC (resistor in series with capacitor in parallel) circuit. In normal operation, the MOSFETs T1 and T2 should never be turn on at the same time. The control logic allows the signals for switching on and off the transistors T1 and T2 to have different logical states in every moment.
If it happens there is an error that can cause the burning of the MOSFETs. In normal operation, it will never happen to lead bought transistors, unless there is an error (software or hardware). The problem is a MOSFETs because they have different time of switching on and off.
Image 2. A delay circuit or an RC circuit
The purpose of the delay circuit shown on the image above is to neutralize or reduce the different delay of the MOSFETs. While an image below shows an increase of the voltage at the output of an RC circuit.
Image 2. A delay circuit (an RC circuit) voltage waveform
Four BUZ11 MOSFETs are used as powerful transistors in a H-bridge. These MOSFETs have their own parasitic diodes with the same current capabilities as the MOSFET. However, antiparallel faster diodes are added. The usage of these diodes is mandatory, especially in high-frequency applications.
How to reduce the impact of interference and disturbances in DC motor driver?
A DC motor driver power supplies
Two sources of power supply are noticed (Vcc Motor and Vcc MCU). The battery power (Vcc Motor) is marked in red, while the control logic power supply (Vcc MCU) is marked in orange. Power supplies are galvanically separated through the integrated circuit IR2112, which is a part of the MOSFET switching circuit. The advantage of separated power supply for logic (Vcc MCU) and power electronics (Vcc Motor) solves problems with the disturbances. See Image 1 for the details.
A DC motor driver is designed onto separated PCBs
A second way of reducing the impact of interference and disturbances, the DC motor driver is designed onto two PCBs (Printed Circuit Board). On the first PCB is mounted the Current limiter circuit, Control logic circuit, Delay circuit and MOSFETs switching circuit. There is a H-bridge on the second PCB. PCBs are shown with deshed lines in Image 1.
Each of the blocks will be described in the following articles.
More about basics of a DC motors you can find out in our tutorials: “DC motors – Basic characteristics and mathematical model” and “DC Motors – voltage, current, speed, power, losses and torque relationships“.
Tutorials in the category: DC motors and drivers