Power Conversion / design models
SMPS Design
Explore AC-mains and DC-input isolated flyback supplies, calculate a first-pass DCM operating point, and follow energy through an interactive circuit.
Answer first
How do I estimate a DCM flyback SMPS operating point?
Use this flyback SMPS designer to estimate duty cycle, primary inductance, turns ratio, peak current, and semiconductor stress for a discontinuous-conduction operating point. The result gives you a first design to examine, not a production-ready mains supply. Magnetics, snubbers, feedback stability, isolation, EMI, and safety still need engineering review.
One topology / Two input arrangements
Where does the power come from?
Both use a fixed-frequency DCM flyback model. Changing mode loads its example values. The existing buck tool is a different, non-isolated step-down topology.
Mains safety: rectified mains can be lethal and capacitors can remain charged after unplugging. This is an educational estimator, not a safe-to-build schematic. Do not prototype the mains stage on a solderless breadboard. A transformer symbol does not certify isolation. A qualified design review and hardware testing are required.
01 / Targets and assumptions
Set the operating point
ON + transfer must stay below 100%. Remaining time is idle. Example values illustrate the model; they are not recommended component ratings.
02 / Follow one switching cycle
Mains-fed flyback
- Primary DC bus
- 271.3–356.4 V
- T1 · primary Lm
- 3608 µH
- T1 · Np : Ns
- 16.88 : 1
- Cout · ideal minimum
- 60.06 µF
- DC output
- 12 V
Component-level power stage, not a finished supply: input filtering and protection, clamp/snubber, feedback, controller supply and compensation still require design. Cbulk is shown but not sized. Gold marks the selected switching-current path; it does not model the AC bridge charging pulses.
Scroll horizontally on a small screen. Gold shows the highlighted path; dashed control lines are not power wires.
The primary switch is ON. Primary current rises from zero and energy builds in the magnetic field. The secondary diode is reverse biased; the output capacitor supplies the load.
Flyback magnetics
This is a coupled energy-storage inductor, often called a flyback transformer. The calculated ratio Np/Ns is not a winding recipe. Core material, effective area, gap, saturation, losses, insulation, creepage and leakage inductance require a separate magnetic design. Dot markers show winding polarity.
03 / Analytical results, not a bill of materials
First-pass design estimates
Calculations include the entered secondary diode drop but otherwise assume lossless transfer, ideal coupling and fixed frequency. At higher input voltage the controller must reduce ON time. Voltage stresses shown are ideal lower estimates; they omit leakage spikes and ringing. Do not select parts directly at these numbers.
How the calculation works
D is the ON fraction, D₂ is the secondary energy-delivery fraction, and 1 − D − D₂ is idle. Estimates apply to the specified full-load operating point. Startup, light-load behavior and transient control are outside this model.
Technical reference: TI — Designing a DCM flyback converter ↗What must still be designed?
Core and winding construction; isolation barriers; controller and gate drive; feedback compensation; current limiting; startup and auxiliary supply; snubber/clamp; input filtering; fuse, surge and inrush protection; capacitor ripple-current ratings; thermal behavior; layout and EMC. This tool does not generate an approved mains power supply.
Design guide
Use the result with engineering context
Technical content reviewed
When this tool is useful
- Comparing an AC-input flyback with a DC-input isolated converter
- Checking whether a target power and switching frequency produce practical first-pass stresses
What the result includes
- Duty cycle, turns ratio, primary inductance, and peak current
- Estimated MOSFET, diode, and winding stress for the selected operating point
What the model does not guarantee
- The model does not design insulation, creepage, clearance, EMI filtering, or a certified transformer
- It does not replace loop-compensation, leakage-inductance, snubber, thermal, and bench validation
Worked approach
Start with the energy path
Enter the input range, output target, efficiency estimate, and switching frequency. Compare the calculated stresses with realistic controller, MOSFET, diode, core, and winding limits before selecting parts.
Common decisions
Questions engineers ask
Is this enough to build a mains-powered SMPS?
No. Mains designs require isolation, protection, transformer construction, creepage, clearance, fusing, EMI, thermal, and regulatory work that a browser calculator cannot approve.
Why does switching frequency change the transformer design?
A higher frequency transfers energy in shorter cycles and can reduce the inductance and core size, but it also raises switching, magnetic, gate-drive, and EMI losses.
What should I verify in a controller datasheet?
Check startup behavior, maximum duty cycle, current-sense threshold, gate-drive capability, compensation method, protection modes, and the voltage range used by the controller itself.
Related build evidence
AgriBot system architecture
See how power, sensing, control, connectivity, and an operator interface fit inside one embedded system. This project is system evidence, not a claim that it uses the flyback values shown here.
See the projectApply it to real hardware
Need a power stage reviewed as part of a prototype?
Send the input range, output rails, load profile, isolation need, size limit, and parts you have already considered.
Discuss the system