This project involves designing a non-isolated buck converter that steps down a 24V input to a 5V output with an efficiency of at least 90%. The buck converter is essential in many power conversion applications, such as power supplies and electric vehicles.
- Input Voltage (Vin): 24V (±2% tolerance)
- Output Voltage (Vout): 5V (±0.01V)
- Input Current: 1A max
- Maximum Output Current: 4.32A
- Efficiency: ≥ 90%
- Form Factor: Max PCB size of 10 cm x 5 cm
A buck converter reduces the input voltage to a lower output voltage by switching a MOSFET on and off. The energy is stored in an inductor and smoothed out by a capacitor. The main components are:
- Schottky Diode (1N5817): The diode is forward biased when the NMOS is open switch, hence it allows the flow of current through it. When NMOS is closed, it is reverse biased, hence inductor starts storing energy. It also minimizes energy losses as compared to conventional diodes.
- PWM Source (NE555 Timer): Generates the switching signal of frequency 500kHz and Duty cycle(20.8%) to switch the circuit between input voltage and Schottky Diode.
- Inductor and Capacitor: For storing energy in the form of magnetic field and powering the circuit when NMOS is open switch, an inductor is used with ripple current = 0.2 * I_maxout. The capacitor is used for output voltage smoothing.
Efficiency depends on losses in the MOSFET (switching and conduction losses), inductor, and other components.
The circuit was simulated to verify the design, focusing on:
- Input voltage (24V DC)
- PWM signal generated by the NE555 (duty cycle 20.8%)
- Output voltage (5V with 0.02V ripple)
Simulation Graphs:
- Green: 24V input voltage
- Blue: PWM signal from the NE555 timer
- Red: 5V output DC voltage
- Schematic: Designed using KiCad, featuring a PWM generator (NE555), MOSFET, Schottky diode, inductor, and output capacitor.
- PCB Design: A dual-layer design to ensure proper thermal management, minimized noise, and correct trace width for current handling.
The buck converter successfully steps down 24V to 5V with over 90% efficiency, meeting all design and dimensional constraints.