Two Quadrant Operation Of Dc Motor For Low Power Applications Using PWM
N.MOHAN RAJ, SASTRA Deemed University
In the modern world, the industrial growth created a revolution in satisfying various human needs. Electrical machines form the backbone of many automated industries, powered from either conventional or renewable sources. In general, the machine can be either a motor or generator depending upon the power absorbed from the source or acting as a source. Moreover, a variety of applications prefer the usage of motors being operated on AC or DC supply. Here a cost-effective solution is developed on accounting to speed and direction control applications relating to DC motor.
Various components incorporated in the circuit are 555 Timer IC acting as an astable multivibrator for generating PWM pulses required for duty ratio control thereby varying the voltage provided to the permanent magnet motor to achieve controllable speed. The motor driver IC decides the direct control of the motor. Motion control for DC motor although looks simple but control over applications is very complex and it needs to be more precise. The circuit design does not incorporate microcontroller. The absence of a microcontroller in the design makes it easy for control without enhancing programmable capabilities.
the working principle of PMDC motor is just similar to the general working principle of DC motor. That is when a carrying conductor comes inside a magnetic field, a mechanical force will be experienced by the conductor and the direction of this force is governed by Fleming’s left-hand rule. As in a permanent magnet DC motor, the armature is placed inside the magnetic field of the permanent magnet; the armature rotates in the direction of the generated force. Here each conductor of the armature experiences the mechanical force F = B.I.L Newton where, B is the magnetic field strength in Tesla (Weber / m2), I is the current in Ampere flowing through that conductor and L is the length of the conductor in meter comes under the magnetic field. Each conductor of the armature experiences a force and the compilation of those forces produces a torque, which tends to rotate the armature.
This is the circuit we employed in the project. The components described above are used along with some resistors of 100R, a variable pot resistance of 100K to vary the width of the pulse and along with two IN4148 diodes.
When power is supplied, 555 TIMER generates a PWM signal with a duty ratio based on the pot resistance ratio. Due to the pot and the diode pair, here the capacitor (which triggers the output) must charge and discharge through a different set of resistance and because of this, the capacitor takes a different time to charge and discharge. Since the output will be high when the capacitor is charging and is low when the capacitor is discharging, we get a difference in high output and low output times, and so the PWM.
This PWM of the timer is fed to the signal pin of L239D h-bridge to drive the DC motor. With the varying PWM ratio, we get varying terminal voltage and so the speed. To change the direction of the rotation the switch position must be interchanged.
Let’s consider a Motor connected on left side output pins (pin 3,6). For rotating the motor in a clockwise direction, the input pins have to be provided with Logic 1 and Logic 0.
Pin2 = Logic1 and Pin7 = Logic0 | Clockwise Direction
Pin 2 = Logic 0 and Pin 7 = Logic 1 | Anticlockwise Direction
Pin 2 = Logic 0 and Pin 7 = Logic 0 or Pin 2 = Logic 1 and Pin 7 = Logic 1 | Idle [No rotation]