Page 330 - Electronic Mechanic - TP - Volume - 2

ELECTRONICS MECHANIC - CITS

EXERCISE 221: Construct the PWM circuit for the speed
control of DC shunt motors

Objectives

At the end of this exercise you shall be able to:
• to demonstrate Introduction of PWM circuit
• to demonstrate DC shunt motors.

Requirements

Tools/ Equipments/ Instruments Materials/ Components
• Neon tester • DC power supply
• Wire stripper • MOSFET or PWM controller
• Screw driver • Diode (to protect against back EMF)
• Combination plier • Potentiometer (for speed control)
• Cotton clothes • DC shunt motor

Note:
• PWM Control: This could be a dedicated PWM controller or a microcontroller generating PWM signals. The
duty cycle of the PWM signal determines the average voltage supplied to the motor, controlling its speed.
• MOSFET: If using a discrete MOSFET, it would be connected to the PWM control signal. MOSFETs are often
preferred for their high switching speeds and efficiency in PWM applications.
• Diode: Connected across the motor terminals in reverse polarity to protect the circuit from back EMF generated
by the motor when it is turned off. This diode allows the current to circulate safely when the motor is turned off,
preventing damage to other components.
• Potentiometer: This is used for speed control. By adjusting the potentiometer, the voltage supplied to the
PWM controller can be varied, thus changing the duty cycle of the PWM signal and consequently the motor
speed.
• DC Shunt Motor: The motor to be controlled. It’s connected between the positive supply and the MOSFET.

Procedure

1 Gather Components: Collect all the necessary components listed in the schematic diagram, including the DC
power supply, MOSFET or PWM controller, diode, potentiometer, and the DC shunt motor.
2 Check Ratings: Make sure that all components are rated appropriately for the voltage and current requirements
of the DC shunt motor. Check datasheets for MOSFETs and diodes to ensure they can handle the expected
current and voltage.
3 Circuit Assembly:
• Connect the positive terminal of the DC power supply to the common terminal of the potentiometer.

• Connect one end of the potentiometer to the input pin of the PWM controller or MOSFET.
• Connect the other end of the potentiometer to the ground (GND) terminal of the power supply.
• Connect the output pin of the PWM controller or MOSFET to the positive terminal of the DC shunt motor.
• Connect the negative terminal of the DC shunt motor to the ground (GND) terminal of the power supply.
• Place the diode across the terminals of the motor, ensuring it is oriented correctly to allow current flow when
the motor is turned off.

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