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Buck Converter Example

Step-down DC-DC converter with voltage mode control.

Overview

The buck converter is the fundamental step-down topology, converting a higher DC voltage to a lower DC voltage with high efficiency.

Specifications

Parameter Value
Input Voltage 48V DC
Output Voltage 12V DC
Output Power 100W
Switching Frequency 100 kHz
Inductor 47 µH
Output Capacitor 220 µF

Circuit Files

  • buck_basic.ipes - Open-loop buck converter
  • buck_voltage_mode.ipes - Voltage mode control
  • buck_current_mode.ipes - Peak current mode control

Theory

Operating Principle

Switch ON (0 < t < DTs): - Inductor current ramps up - Energy stored in inductor

Switch OFF (DTs < t < Ts): - Inductor current ramps down through diode - Energy transferred to output

Key Equations

Voltage Conversion Ratio: $\(\frac{V_{out}}{V_{in}} = D\)$

Inductor Current Ripple: $\(\Delta I_L = \frac{V_{in} - V_{out}}{L} \cdot D \cdot T_s\)$

Output Voltage Ripple: $\(\Delta V_{out} = \frac{\Delta I_L}{8 \cdot f_s \cdot C}\)$

Simulation Results

Steady-State Waveforms

Expected measurements: - Output voltage: 12.0V ± 0.1V - Inductor current ripple: ~2A peak-to-peak - Output voltage ripple: <50mV

Startup Transient

Soft-start implementation limits inrush current.

Exercises

  1. Duty Cycle Sweep: Vary D from 0.2 to 0.8, measure Vout
  2. Load Step Response: Apply 50% load step, measure recovery time
  3. CCM/DCM Boundary: Find minimum load for CCM operation
  4. Efficiency Analysis: Enable loss models, measure efficiency vs load