Purpose: To understand the design and working of a Buck converter used to step down DC voltage efficiently.
Main Concept: A buck converter uses a switching element (like a MOSFET) to create a PWM signal and components like inductors, capacitors, and diodes to smooth the output voltage.
Buck Converter Basics
PWM Signal: Generated by periodically turning a switch on and off. The duty cycle (percentage of time the switch is on) determines the average output voltage.
MOSFET Usage: Acts as an electrical switch controlled by a PWM signal.
Smoothening Components
Inductor: Placed in series with the load. It smooths the voltage by resisting changes in current and storing energy in its magnetic field.
Capacitor: Placed in parallel to the load to stabilize the voltage by resisting changes in voltage and storing energy in its electric field.
Schottky Diode: Provides a pathway for electrons when the switch is open, preventing high negative voltage spikes.
Working of Individual Components
Inductor
Switch On: Current starts to flow, inductor creates opposing voltage, eventually stabilizes allowing maximum current.
Switch Off: Inductor supplies current as it can't change current instantly, eventually runs out of energy.
Capacitor
Switch On: Capacitor charges, resists increase in voltage by balancing the potential difference.
Switch Off: Capacitor discharges, acts as a battery momentarily then runs out of energy.
Complete Circuit Operation
Feedback Mechanism: To maintain stable output voltage despite load changes by adjusting PWM signal duty cycle.
Components in the Circuit
Op-Amp (Operational Amplifier): Amplifies difference between non-inverting & inverting inputs.
Triangle Wave Generator: Provides waveform for PWM generation.
Comparator: Compares output of error amplifier and triangle wave to produce PWM signal.
Controlling the MOSFET
P-Channel MOSFET: Turns on when gate voltage is below source voltage. Used instead of N-channel MOSFET as it can operate with source voltage close to Vcc -- prevents need for higher gate voltage.
Voltage Regulation & Reference Voltages
Voltage Divider: Scales down output voltage for the error amplifier.
Voltage Reference: Ensures accurate comparison and generation of PWM signal.
Design Considerations
Resistor Values: Ensure error amplifier input stays below reference voltage to maintain accurate operation.
Minimum Output Voltage: Set by feedback components, affects voltage range and stability.
Comparator Inputs: Proper connection crucial for maintaining desired output voltage range.
Summary
Functionality: Converts higher voltage DC to stable lower voltage DC using a combination of PWM, inductors, capacitors, and feedback mechanisms.
Closed-loop Control: Maintains desired output voltage regardless of changes in load by dynamic adjustment of PWM duty cycle.
Key Concept: Efficiently stepping down DC voltage using buck converter involves managing switching elements and smoothening components, ensuring stable output through feedback control.