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Motor drives are circuits used to run a motor. In other words, they are commonly used for motor interfacing. These drive circuits can be easily interfaced with the motor and their selection depends upon the type of motor being used and their ratings (current, voltage).
The major motor drive components for DC motors are: a controller, a motor driver IC or a motor driver circuit, the desired DC motor being used, power supply unit and the necessary connections to the motor.
Servo motor is a type of actuator device that consists of a motor and a sensor to control velocity, acceleration etc. The major motor drive components for a servo motor are a controller, power supply unit, servo motor and the necessary connections with the motor.
Commonly, motor drive for a servo motor is also known as Servo motor controller or Servo Motor Driver. Usually, 8051 controllers are used for controlling a servo motor driver with a single servo motor. If there are multiple servo motors; then PIC, ATMEGA etc. can be used.
Motor Driver circuits are current amplifiers. They act as a bridge between the controller and the motor in a motor drive. Motor drivers are made from discrete components which are integrated inside an IC. The input to the motor driver IC or motor driver circuit is a low current signal. The function of the circuit is to convert the low current signal to a high current signal. This high current signal is then given to the motor. The motor can be a brushless DC motor, brushed DC motor, stepper motor, other DC motors etc.
In motor interfacing with controllers, primary requirement for the operation of the controller is low voltage and small amount of current. But the motors require a high voltage and current for its operation. In other words we can say the output of the controller or processor is not enough to drive a motor. In such a case direct interfacing of controllers to the motor is not possible. So we use a Motor Driver Circuit or Motor Driver IC.
Not only in the case of controllers, while connecting motors with 555 timer ICs or 74 series ICs; they also cannot provide the large current required by the motor. If direct connection is given, there might be a chance of damage to the IC.
Transistor based DC motor driver circuit is one of the simple DC motor driver circuit. It uses a power transistor (D880), DC motor and a resistor for its operation. Let IN be the input to the base of the transistor. To the collector of the transistor, the DC motor is connected. Emitter of the transistor is placed to ground. Normal Vcc given to the circuit is 12volt. Here the main point to note is that, check the DC motor being used. While choosing the transistor and the DC motor; the current rating must be noted. Always the current rating of the DC motor must be smaller than that of the transistor being used. Application of this motor driver circuit is for single direction control of the motor; e.g. Line following Robot.
Input (IN) |
Motor Action |
0 volt |
Motor Stops |
5V |
Motor is in Action |
H bridge circuit is one of the other commonly used motor driver circuit. In robotic applications, were the DC motor has to run in backward and forward direction; H bridge circuits play a major role. The name H Bridge is used because of the diagrammatic representation of the circuit.
Usually the H bridge circuit contains 4 switches S1, S2, S3 and S4. These switches can be relays, or P channel and N channel BJTs, MOSFETs, or they can be N channel MOSFETs only. Here a basic H bridge circuit is shown in the figure below were NPN transistors are placed at the high voltage and PNP transistors to the low voltage.
Transistor Based H-Bridge Circuit
The components used in the circuit are NPN and PNP power transistors, resistors, diodes, a DC motor, and a power supply of about 12V.
Input 1 and Input 2 are the inputs to the H bridge circuit.
IN1 |
IN2 |
A |
B |
Motor Action |
0 |
0 |
0 |
0 |
Stop |
0 |
1 |
0 |
Vcc |
Anticlockwise |
1 (5V) |
0 |
Vcc |
0 |
Clockwise |
1 |
1 |
Vcc |
Vcc |
Brake |
L293D is a dual H bridge motor driver IC. This 16 pin motor driver IC can drive the motors in anti-clockwise and clockwise direction. The connection of the DC motors to L293D IC is given below.
Pin Description of L293D
Operation of L293D controlling two DC motors
Pin1 |
Pin2 |
Pin7 |
Action of Motor |
+5 volt |
0 volt |
0 volt |
Stop |
+5 volt |
0 volt |
+5 volt |
Clockwise |
+5 volt |
+5 volt |
0 volt |
Anti-clockwise |
+5 volt |
+5 volt |
+5 volt |
Stop |
0 volt |
- |
- |
- |
ULN2003 can be used as a motor driver IC. It contains high current and voltage Darlington arrays. This driver IC can be used for driving stepper motors. This is because stepper motor needs more current for its operation in the motor drives. The circuit below shows the ULN2003 with a stepper motor. The input to ULN2003 are K= {0011, 0110, 1100, 1001}; and L= {1001, 1100, 0110, 0011}. These input sequences will energize the two adjacent phases of the stepper motor.
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