The PWM circuit is created by combining an astable multivibrator, an integrator, and a comparator. However, achieving variable frequency operation poses a challenge. This is because adjusting the frequency and integrating resistors’ knobs to match the input frequency, along with modifying the duty cycle knob, becomes necessary.
Op-Amp as Duty Cycle Controller
To simplify this need, a Voltage Controlled Oscillator, as mentioned earlier, is utilized. This feature is specified in the LM 324 IC’s data sheet by the manufacturer. By making specific adjustments and incorporating additional components, it is possible to create a PWM circuit for applications such as motor speed control or adjusting light brightness.
Simulation of Op-Amp as Duty Cycle Controller
The square wave whose frequency can be adjusted with the frequency knob, is converted to a triangular wave. The Duty cycle adjusting knob is used to vary the duty cycle (which is Red line on the triangular wave form in the above image).
When the instantaneous triangular wave voltage is lesser than the dc voltage of duty cycle knob, the output is in High state and vice versa. This can be reversed by reversing the V+ and V- inputs of the output stage Op-Amp.
Simulation – PWM
Pulse-width modulation, also known as pulse-duration modulation. It is a method used to effectively reduce the average power delivered by an electrical signal by breaking it down into discrete segments. Controlling the average voltage supplied to the load is achieved by rapidly toggling the switch between the power supply and the load on and off.
PWM finds applications in various fields, including communications, power control, and conversion. For instance, it is widely employed to regulate the speed of electric motors, adjust the brightness of lights, and in applications like ultrasonic cleaning.
In PWM, low-frequency output signals are generated from high-frequency pulses by swiftly switching the output voltage of an inverter leg between the upper and lower DC rail voltages. The resulting low-frequency output can be perceived as the average voltage over a switching period.