Boost Converter Designer — Inductor, Capacitor, MOSFET & Diode Sizing | CalcEngines

Electronics Calculators

Boost Converter Designer

Name: Boost Converter Designer
Author: CalcEngines

Complete step-up DC-DC converter design tool. Calculate duty cycle, inductor, output capacitor, MOSFET and diode ratings, switching losses, and efficiency. CCM and DCM analysis included.

Step-up DC-DC · CCM/DCM · Full loss analysis · Interactive schematic

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Input / Output Specification

V_in (Input)

V_out (Output)

I_out Max

Switching Parameters

Freq f_sw

kHz

Ripple ΔV_out

ΔI_L Ripple

Target η

MOSFET / Diode / Cap

R_DS(on)

mΩ

Diode V_f

Gate Q_g

Cap ESR

mΩ

V_gs Drive

Key Results

Duty Cycle D

—%

Ideal D (no loss)

—

Practical D (with η)

—

Voltage Gain M

—

Input Current I_in

—

◆ CCM — Continuous Conduction Mode

Min Inductance

—

μH (CCM boundary)

Recommended L

—

μH (with margin)

Output Cap C_out

—

μF minimum

I_L Average

—

I_L Peak

—

ΔI_L Ripple

—

A peak-to-peak

Estimated Efficiency

—

Enter parameters

60%75%85%92%98%

Inductor Specification

Min L (CCM)

—

μH

Recommended L

—

μH (×1.5 margin)

I_L Peak

—

A (saturate ≥ this)

I_L RMS

—

ΔI_L p-p

—

Energy ½LI²

—

μJ

Select an inductor with saturation current ≥ I_L,peak and DCR as low as possible.

Output Capacitor

C_out for ΔV

—

μF

ESR Ripple

—

Total Ripple

—

V p-p

Cap RMS Current

—

Target ΔV_out

—

Voltage Rating

—

V (≥1.5× Vout)

MOSFET Requirements

V_DS Blocking

—

V (= Vout)

I_D Peak

—

I_D RMS

—

R_DS(on)

—

mΩ

Cond. Loss

—

Rec. V_DS Rating

—

V (1.3×Vout)

Diode Requirements

V_R Reverse

—

I_F,avg

—

I_F,peak

—

Diode Loss

—

Component Summary Table

Component	Parameter	Minimum	Recommended	Status

Loss Breakdown

Total Estimated Loss

—W

P_in

—

P_out

—

Calculated η

—

Output/Loss ratio

—

MOSFET Conduction (I²·R_DS)—

MOSFET Switching (Q_g·V·f)—

Diode Conduction (V_f·I_out)—

Inductor DCR (estimated)—

Output Cap ESR—

Calculated Efficiency

—

Calculate to see result

60%75%85%92%98%

Detailed Loss Table

Loss Source	Formula	Value (W)	% of Total	Reduction Tip

Key Waveforms — One Switching Cycle

Inductor Current i_L(t)

MOSFET Gate Signal V_gs(t)

Diode Current i_D(t)

Period T

—

μs

ON time D·T

—

μs

OFF time (1-D)·T

—

μs

Ideal Duty Cycle

D = 1 − (Vin / Vout) Practical: D = 1 − (Vin × η / Vout)

D ranges 0 to <1. Higher D = more voltage boost but more stress. At D > 0.8 efficiency drops sharply.

Voltage Gain

M = Vout / Vin = 1 / (1 − D) Practical: M = Vout / (Vin × η)

Ideal gain is 1/(1−D). At D=0.5 gain=2, at D=0.75 gain=4.

Minimum Inductance (CCM)

L_min = (Vin × D) / (2 × Iout × fsw) = Vout×D×(1−D)²/(2×Iout×fsw)

Inductor must exceed L_min to ensure CCM at full load. Recommended L = 1.5 × L_min.

Inductor Ripple Current

ΔiL = (Vin × D) / (L × fsw) I_peak = I_in + ΔiL/2 I_valley = I_in − ΔiL/2

I_in = Iout / (1−D) — average inductor current in CCM. Peak current must be below inductor saturation rating.

Output Capacitor

C_min = Iout × D / (fsw × ΔVout) ΔV_esr = ESR × ΔiL ΔV_total = ΔV_cap + ΔV_esr

Both capacitive and ESR contributions add to output ripple. Low-ESR capacitors minimise the ESR term.

CCM/DCM Boundary

I_boundary = Vin × D / (2 × L × fsw) DCM if Iout < I_boundary

Below the boundary current the converter enters DCM. Output voltage rises in DCM for the same duty cycle.

MOSFET Losses

P_cond = I_sw_rms² × Rds(on) P_sw = Qg × Vgs × fsw I_sw_rms = sqrt(D)×sqrt(IL²+ΔiL²/12)

Conduction loss scales with I². Switching loss scales with frequency. Minimise both by selecting a low Rds·Qg FOM device.

Diode Loss

P_diode = Vf × Iout

Schottky diodes with low Vf (0.3–0.5 V) minimise diode loss. Synchronous rectification replaces the diode with a MOSFET for very high efficiency.

How a Boost Converter Works

A boost (step-up) converter increases a DC input voltage to a higher DC output voltage using an inductor, a switch (MOSFET), a rectifying diode, and an output capacitor. During the ON phase the MOSFET closes, current ramps up through the inductor storing energy. During the OFF phase the MOSFET opens — the inductor’s collapsing field forward-biases the diode, delivering the stored energy plus the input voltage to the output.

The key relationship is Vout = Vin / (1 − D) where D is the duty cycle. A 50% duty cycle doubles the voltage; 75% quadruples it.

CCM vs DCM: At full load the inductor current stays above zero throughout the cycle (CCM). At light loads the current may reach zero before the next cycle (DCM). CCM offers more predictable gain and lower peak currents.

Frequently Asked Questions

What is the duty cycle formula for a boost converter?

Ideal: D = 1 − (Vin / Vout). Practical with efficiency η: D = 1 − (Vin × η / Vout). For example, boosting 12 V to 24 V at 90% gives D = 1 − (12 × 0.9 / 24) = 0.55 (55%).

How do I calculate the minimum inductor for a boost converter?

L_min = (Vin × D) / (2 × Iout × fsw). Use 1.5× L_min for margin. The inductor saturation current must exceed I_peak = I_in + ΔiL/2.

What causes a boost converter to oscillate or be unstable?

The Right-Half-Plane (RHP) zero in the boost transfer function makes it harder to stabilise than a buck. The RHP zero = (1−D)² × R / L. High duty cycles push this lower, limiting achievable bandwidth.

What MOSFET should I choose for a boost converter?

The MOSFET must handle Vds = Vout (derate to 80%), peak drain current = I_L,peak. Minimise Rds(on) × Qg FOM. Above 200 V consider SiC for lower switching losses.

Calculations are theoretical estimates. Actual performance depends on component parasitics, PCB layout, thermal management and control loop design.
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