Power Electronics Calculators: Buck, Boost & Flyback Converters

Interactive workspace initializes in your browser. Engineering method, assumptions, validation, and references are available below.

Engineering reference

Power Electronics: theory, method, and sources

This electrical engineering workspace publishes 7 governing equations, 3 stated assumptions, 1 documented boundary, 1 worked example, 1 validation case, and 3 sources so the numbers it returns can be checked rather than taken on trust.

Calculations run locallyContent reviewed September 8, 2026Calculation & source methodology

How this tool works

Eleven guided modules cover regulator efficiency, ideal converter relationships, magnetic ripple, semiconductor losses, thermal design, and full power budgets.

All plots label voltage, current, time, power, temperature, duty cycle, and efficiency units explicitly.

Numerical inputs, imported state, text lists, and graph samples are bounded before calculation and rendering.

Engineering theory

Voltage direction, timing, and power balance

A buck converter reduces voltage; a boost converter raises it. Entering a buck target above its input, or a boost target below it, does not become valid by clipping the duty cycle. This workbench rejects those combinations and explains which topology can support the requested direction. Ideal high-duty ratios are retained, with a warning that actual minimum off-time, switch loss, and control limits may make them impractical.

For buck, boost, and inverting buck-boost, the triangular ripple estimate assumes continuous conduction. If the calculated current valley reaches zero, the conduction mode changes and the CCM equation set no longer predicts a diode-based DCM operating point. The displayed waveform is then an extrapolation used to identify the model boundary. Efficiency is an entered power-budget assumption, not a prediction of a particular controller or semiconductor.

DCM flyback timing must fit inside a cycle

In the ideal discontinuous flyback, primary current starts at zero and rises according to di/dt = Vin/Lp. The requested peak current therefore sets the on-time. During secondary conduction the primary-referred current falls to zero under the reflected output voltage. Both intervals must fit within one switching period, leaving an idle interval for discontinuous operation. At zero idle time the converter is at the boundary.

A CCM voltage-ratio equation alone cannot set DCM duty while an independent peak current is used to calculate transferred energy. This model instead derives on-time and demagnetization time from the same peak current, inductance, turns ratio, and voltage inputs. It rejects inconsistent timing. The graph shows primary-referred magnetizing current; it is not the primary switch-current waveform during the secondary conduction interval.

Inputs and outputs explained

Inputs

Converter voltage targetsV: Use positive input and output magnitudes and the correct step-up or step-down topology. The inverting model reports a negative output voltage.
Flyback turns ratioNs/Np: Secondary turns divided by primary turns. The primary sees an ideal reflected output voltage of Vout/(Ns/Np).
MOSFET RMS currentA during on-time: Use RMS current over the conducting interval when applying the separate duty factor. Full-cycle RMS already includes duty and must not be multiplied by duty again.

Outputs

Thermal feasibility: A negative allowable sink resistance means the package and interface already exhaust the thermal budget. Even an ideal passive heatsink cannot meet the target.
Power-budget efficiency%: Losses must not exceed input power. Gate-drive power is part of the system budget and is not all dissipated in the MOSFET junction.

Calculators and topics covered

power electronics
DC-DC converters
buck
boost
flyback
switching losses
thermal design
linear regulator
duty cycle
inductor ripple
capacitor ESR
MOSFET loss
diode recovery
heatsink

Core equations

D \approx \frac{V_{\mathrm{out}}}{V_{\mathrm{in}}}

\Delta IL = \frac{V_L \cdot D}{Lf}

Pcond = I_{\mathrm{on,rms}}^{2} R_{DS} \left(on\right) D

Psw \approx \frac{1}{2} VI \left(tr + tf\right) f

Tj = Ta + P\sum \theta

\eta = \frac{P_{\mathrm{out}}}{P_{\mathrm{in}}}

\text{DCM flyback:}\quad \begin{gathered}t_{on} = \frac{Lp \cdot I_{\mathrm{pk}}}{V_{\mathrm{in}}}\\t_{\mathrm{demag}} = \frac{Lp \cdot I_{\mathrm{pk}} \cdot \left(\frac{Ns}{Np}\right)}{V_{\mathrm{out}}}\\t_{on} + t_{\mathrm{demag}} \le \frac{1}{f}\end{gathered}

Worked examples

A feasible DCM flyback

Use Vin = 12 V, Vout = 5 V, Ns/Np = 1, Lp = 100 µH, f = 100 kHz, Ipk = 0.2 A, and 85% assumed efficiency.

Method

The period is 10 µs. The on-time is 100 µH × 0.2 A / 12 V = 1.667 µs.
Demagnetization takes 100 µH × 0.2 A / 5 V = 4 µs, leaving 4.333 µs idle.
Stored energy per cycle is ½ × 100 µH × (0.2 A)² = 2 µJ. Multiplying by 100 kHz gives 0.2 W.

Result: On-time duty is 16.67%, estimated output power is 0.17 W, and output current is 0.034 A.

Interpretation: Raising the peak current to 2 A with all other settings unchanged would require 56.67 µs for charging plus demagnetization. That cannot fit the 10 µs cycle and is rejected.

Common mistakes

Hiding an impossible thermal target

Rounding a negative required heatsink resistance to zero and presenting it as achievable.

Better approach: Reduce dissipation, ambient temperature, or junction/interface resistance before choosing a heatsink.

Treating a negative current valley as a real diode current

Interpreting the CCM triangular extrapolation below zero as the converter response.

Better approach: Use the warning to identify the conduction boundary. A DCM model or suitable hardware model is needed beyond it.

Method and assumptions

Assumptions

Buck, boost, and inverting buck-boost use ideal steady-state CCM ratios with a separate lumped efficiency estimate. A nonpositive current valley is flagged as outside the CCM assumption.
Efficiency is entered as a lumped assumption in converter modules.
Flyback calculations use a simplified discontinuous energy-transfer model.

Limitations and design boundaries

Not a substitute for magnetic core design, control-loop compensation, switch-node ringing analysis, isolation safety, creepage/clearance review, EMI testing, device SOA verification, PCB layout analysis, or regulatory compliance.

Validation cases

These checks document how representative calculations are cross-checked against analytic or reference results.

Validation policy

DCM timing and energy

Analytic cross-check

Method: Calculate charging time, demagnetization time, and energy independently from the inductor voltage/current relationships.
Expected: 1.667 µs on-time, 4 µs demagnetization, 0.2 W input energy rate for the worked example.

Sources and references

Primary sources are preferred for ratings, standards, manufacturer data, and externally defined constants.

Source policy

Texas Instruments: Designing a DCM flyback converterCharging, demagnetization, and idle intervals in discontinuous flyback operation.
Erickson and Maksimović, Fundamentals of Power ElectronicsConverter steady-state models, ripple, loss, and control foundations.
Mohan, Power ElectronicsPower-semiconductor devices, converters, and thermal considerations.