Flyback converter
CCM, DCM and valley-delayed quasi-resonant energy-transfer models with leakage-clamp sizing.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
DCM energy: PO = ½ LP IPK² fs; D = LP IPK fs/VIN; D2 = LP IPK fs/(n VO)
Assumptions
- Ideal magnetizing energy transfer and output rectifier; magnetizing inductance is primary-referred. Primary/secondary current ratio follows the entered turns ratio.
- QR mode uses complete demagnetization followed by a fixed valley delay of (valley − 0.5)/fring. It does not claim a measured controller frequency or zero-voltage switching.
- RCD clamp loss includes continuing magnetizing energy during leakage discharge. Constant clamp voltage, small ripple and full leakage-energy capture are assumed.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Operating mode
- auto
- Minimum input
- 80 V
- Nominal input
- 120 V
- Maximum input
- 180 V
- Output voltage
- 12 V
- Output current
- 2 A
- Turns ratio Nprimary / Nsecondary
- 6
- Primary magnetizing inductance
- 0.0003 H
- Fixed switching frequency
- 100000 Hz
- Drain resonant frequency for QR
- 2000000 Hz
- QR valley number
- 1
- Primary leakage inductance
- 0.000003 H
- Clamp voltage above input rail
- 120 V
- Allowed RCD clamp ripple
- 10 V
- Effective output capacitance
- 0.00047 F
- Output-capacitor ESR
- 0.03 Ω
Results
- Nominal switch duty
- 0.316228
- Nominal conduction mode
- DCM
- Nominal switching frequency
- 100000 Hz
- Reflected output voltage
- 72 V
- Maximum primary peak current
- 1.26491 A
- Nominal switch RMS
- 0.410676 A
- Nominal secondary RMS
- 3.18108 A
- Maximum clamped drain voltage
- 300 V