Switch-Mode Power Supplies: Buck & Boost Topologies

1. Overview & Concept Definition

High-efficiency electronic power conversion topologies that transform DC input voltages up or down using semiconductor switches (MOSFETs), inductors, diodes, and capacitors.

2. Engineering & Industrial Significance

Unlike linear regulators (LDOs) which dissipate voltage drop as pure heat ($P = (V_{in} - V_{out}) \times I$), switch-mode converters achieve 85% to 96% energy efficiency, crucial for battery-powered robotics, electric vehicles, and embedded microprocessors.

3. Physical Working Principle & Transducer Dynamics

In Continuous Conduction Mode (CCM), energy is periodically stored in an inductor's magnetic field during switch ON time ($t_{on} = D \cdot T$) and discharged to the load through a freewheeling diode or synchronous MOSFET during OFF time ($t_{off} = (1-D) \cdot T$). Volt-second balance across the inductor ($L \frac{di}{dt}$) dictates steady-state transfer ratios.

// ANSI C: Sizing Inductor & Capacitor for a Synchronous Buck Converter
#include <stdio.h>

void calculate_buck_components(float vin, float vout, float iout_max, float f_sw_hz) {
    float duty = vout / vin;
    float delta_il = 0.30f * iout_max; // Standard rule: 30% inductor current ripple
    
    // Required inductance L = (Vin - Vout) * D / (f_sw * Delta_IL)
    float l_henries = ((vin - vout) * duty) / (f_sw_hz * delta_il);
    
    // Required capacitance for 1% voltage ripple: Cout = Delta_IL / (8 * f_sw * Delta_Vout)
    float delta_vout = 0.01f * vout;
    float c_farads = delta_il / (8.0f * f_sw_hz * delta_vout);
    
    printf("[Buck Converter Sizing] Vin=%.1fV, Vout=%.1fV, Iout=%.1fA, f_sw=%.0f kHz\n", 
           vin, vout, iout_max, f_sw_hz / 1000.0f);
    printf("Duty Cycle (D): %.2f%%\n", duty * 100.0f);
    printf("Recommended Inductance: %.2f uH (I_sat >= %.2f A)\n", 
           l_henries * 1e6f, iout_max + (delta_il / 2.0f));
    printf("Recommended Output Capacitance: %.2f uF\n", c_farads * 1e6f);
}

6. Common Engineering Pitfalls & Troubleshooting

7. Applications & Physical Constraints