Assignment on H bridge motor driver circuit

 Abstract of H bridge motor driver circuit

The purpose of the report is to design the H-bridge DC motor driver circuit that can turn the Motor ON/OFF as well as change the direction. A lot of applications that have automated parts use DC motors. DC motors can do different things which normal human being can do like lifting weights which are too heavy, moving things to different locations along with other many useful applications. Variable speed and user control are usually required in these types of applications which can be achieved with the use of power supple, H-bridge and a control signal. In many ways, the speed of a motor can be controlled like on-off, reverse rotation of a dc motor etc. In the below circuit different component like BJT, relay and power transistor are used. The simulation circuit is of 2 channel DC motor drive which use transistor as its main component which is used to control the rotation direction of motor and also the on and off state of the motor. This circuit is economical to build as well. 

Introduction of H bridge motor driver circuit

Many electrical systems and control system use DC motors e.g. we can commonly find DC motor in automotive controller systems, in robotics applications, in powered wheelchairs, hand drills etc. Lost cost and simplicity make DC motors a preferred choice. DC motors need to controlled as they are required to be operated at the desired speed, and they are also required to move in both and reverse directions (Phan, 2011). To do all this drive circuit is needed. Brushed DC motors are very easy to control as they do not require any manual input or drive to operator. Speed of a DC motor is relatively easy to control as the relationship between the input voltage and speed of motor is relatively linear (Gupta, , 2010).

 Generally, a variable potentiometer or a variable resistor is used to achieve variable speed. The main issue with using transistor is heating of transistors which decrease the efficiency of motor driving systems. To overcome this issues, Pulse Width Modulation PWN DC motor control system is used. PWM adjust the speed of motor by giving power/voltage in short pulses. “Duty cycle” is the fill rate of a PWM signal. The speed of a motor changes according to the duty cycle. Motor will rotate faster is the duty cycle is higher and similarly lower if duty cycle is lower (George, 2019)

            The below circuit is an H-bridge circuit because BJTs form the two vertical lines like in alphabet “H” and motor forms the horizontal line of “H”. It the simple yet elegant circuit which is found in all the motor drives. The direction and the speed of a DC motor can be easily controlled with this  (Vivekanand, 2019)

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Figure: H-Bridge Motor Driver Circuit (Vivekanand, 2019)

Parts List

§  DC motor

§  Resistors

§  Diode

§  BJT (bd140, BD241, BD242)

§  Voltage source

§  Ground

§  Ammeter

§  Voltmeter  

            Calculations of H bridge motor driver circuit

The equivalent circuit of DC is shown as in below figure

DC motor equivalent circuit

Below steady state operations there is a time derivative zero, and suppose the motor is not saturated; so the field circuit is;

The induced e.m.f is also at the reverse direction where the  is the instantaneous speed , and the timing average values for the operation of steady states also gives result

Usually PWM signals are used to control the direction and speed of a DC motor. PWM signals can vary the applied voltage to the winding of a DC which results in varying speed of the motor. The increase in voltage results in increased speed. The average voltage which is fed to the load is controlled by turning the switch between supply and load on and off at an enormously high pace. If the switch is on for more time than it is off, more power will be supplied to the load. The duty cycle is a measure of proportion of on time a full period. Higher duty cycle translates to more power because the power is on for most of time (Özer et al , 2017). 

Below figure illustrates the principle of a PWM signal where high duty results in higher applied voltage to motor and similarly, lower duty cycle results in lower voltage:

Simulation circuit of H bridge motor driver circuit

In the below simulation circuit is of 2 channel DC motor drive which use transistor as its main component which is used to control the rotation direction of motor and also the on and off state of the motor (Eleccircuit.com, 2020).There are two different components which contribute the diode 5, and diode 6 and it could also protect the circuit and transistors do not damage. If there both inputs are 0 at the same time  

 Conclusion of H bridge motor driver circuit

Summing up all the discussion it is concluded that, the design H-bridge DC motor is implemented as shown in the above simulations part. The H-bridge DC motor is very easy and simple methods to control the direction of motor as well as On/OFF state. DC motor driver circuit can control in both direction reverse and forward. The NPN- and PNP type of MOSFET is used in the H-bridge circuit.