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Boost Converter Design Calculator

Calculate duty cycle, inductor value, and output capacitor for boost (step-up) DC-DC converter design

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Formula

D=1−Vin/(Vout×η),L=Vin×D/(ΔIL×fsw)D = 1 - V_in/(V_out×η), L = V_in×D/(ΔI_L×f_sw)

Reference: Erickson & Maksimovic, "Fundamentals of Power Electronics" 3rd ed.

D— Duty cycle
V_in— Input voltage (V)
V_out— Output voltage (V)
η— Efficiency
f_sw— Switching frequency (Hz)
ΔI_L— Inductor current ripple (A)

How It Works

The boost converter calculator computes duty cycle, inductor value, and capacitor requirements for step-up DC-DC conversion — essential for battery-powered LED drivers, USB PD applications, and energy harvesting systems. Power electronics engineers, portable device designers, and solar MPPT developers use this tool to efficiently increase voltage from low-voltage sources. According to Erickson & Maksimovic's 'Fundamentals of Power Electronics', boost converters achieve 92-96% peak efficiency with the fundamental relationship D = 1 - (Vin/Vout) determining the duty cycle in continuous conduction mode. During the switch on-time, inductor current builds linearly at rate dI/dt = Vin/L; during off-time, the inductor voltage adds to Vin, forcing current through the diode to the output. TI application note SLVA372 specifies inductor value L = Vin × D / (fsw × ΔIL), where ΔIL represents 20-40% of average inductor current for optimal CCM operation. Output capacitor ripple current equals Iout × √(D/(1-D)), requiring low-ESR ceramics to maintain <50 mV ripple. Critical consideration: boost converters cannot limit inrush current or prevent output-to-input backfeed without additional protection circuits.

Worked Example

Design a boost converter for a single-cell Li-ion (2.7-4.2 V) to 5 V USB output at 2 A. Target specifications: >90% efficiency across input range, <50 mV output ripple, 1 MHz switching frequency. Step 1: Calculate duty cycle at minimum Vin — D = 1 - 2.7/5 = 0.46 (46%). Step 2: Calculate inductor current — Iin_max = Pout/(η × Vin_min) = 10 W/(0.9 × 2.7 V) = 4.1 A. Step 3: Select inductor for 30% ripple — ΔIL = 0.3 × 4.1 = 1.23 A. L = 2.7 × 0.46/(1M × 1.23) = 1.0 µH. Use 1.0 µH Coilcraft XAL5030 (8.5 A Isat, 12.5 mΩ DCR). Step 4: Calculate output capacitor — Cout = 2 A × 0.46/(1M × 0.05 V) = 18.4 µF. Use 2 × 22 µF/6.3V X5R ceramics. Step 5: Select IC — TI TPS61088 (10 A switch, 1.2 MHz, 95% peak efficiency). Step 6: Verify thermal — Power loss ≈ 10 W × 0.08 = 0.8 W at 92% efficiency, requiring θJA < 75°C/W for 85°C ambient operation.

Practical Tips

  • ✓Per Analog Devices AN-1106, select Schottky diodes with 150% voltage rating (7.5 V for 5 V output) and 200% current rating (4 A for 2 A output) to handle switching transients and thermal derating
  • ✓Use input current sensing for MPPT applications — solar panels require ≤0.1 V sense voltage to maintain >98% tracking accuracy per TI SLVA446
  • ✓Implement soft-start (1-10 ms) to limit inrush current — boost converters see Vin/Rdson inrush before the control loop stabilizes, potentially exceeding switch current rating

Common Mistakes

  • ✗Undersizing the inductor saturation current — at 46% duty cycle with 2 A output, inductor peak current reaches Iin + ΔIL/2 = 4.7 A; a 3 A inductor saturates, causing thermal runaway
  • ✗Ignoring output diode reverse recovery — standard PN diodes exhibit 50-200 ns recovery time, causing 5-10% efficiency loss at 1 MHz; use Schottky diodes (5 ns recovery) or synchronous rectification
  • ✗Neglecting input-to-output energy backfeed — battery-powered systems require load disconnect switch to prevent output capacitor from discharging back through the boost when shutdown

Frequently Asked Questions

Per Mohan's 'Power Electronics' textbook, efficiency losses include: switch conduction (Irms² × Rds(on)) at 2-4%, diode forward voltage drop (Vf × Iout) at 2-5%, switching losses at 1-3%, and inductor DCR at 1-2%. Synchronous boost converters replace the diode with a low-Rds(on) MOSFET, reducing losses from 5% to <1% — critical for low Vin/Vout ratios where diode drop becomes significant.
Higher frequencies enable smaller inductors (L ∝ 1/fsw) but increase switching losses. TI recommends: 100-500 kHz for >10 W applications, 500 kHz-2 MHz for portable devices, 2-4 MHz for miniaturized designs. At 2 MHz, a 5 V/2 A boost uses 0.47 µH inductor (2.5×2.5 mm) versus 4.7 µH (6×6 mm) at 200 kHz.
Yes — modern boost controllers support 10:1 input range. TI TPS61178 operates from 2.7-30 V input to 40 V output. Wide-Vin designs require: (1) duty cycle limiting at D > 90% to maintain stability, (2) slope compensation to prevent subharmonic oscillation, (3) current-mode control for faster transient response across the operating range.
Boost converters have a right-half-plane zero (RHPZ) at fz = (1-D)² × R/(2π × L), causing 90° phase lag. At D = 0.5, 1 µH inductor, 5 Ω load: fz = 200 kHz. Crossover frequency must stay below fz/3 for >45° phase margin. Solutions: reduce bandwidth, increase inductance, or use current-mode control (shifts RHPZ higher).
Boost converters require both peak current limiting and average current limiting. Per TI SLVA535: cycle-by-cycle limiting protects the switch (triggers at 120-150% of Ipk_design), while average limiting prevents inductor saturation during soft-start and output short circuits. Hiccup mode (off for 10-100× the soft-start period) limits thermal stress during sustained faults.

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