Main Switching Parameters
Output Winding 1
Optional Secondary Windings
Please enter valid values. Frequency, efficiency, AL, input voltage and output 1 values must be greater than zero.
RESULTS
Primary to Secondary 1 Ratio
Input Parameters Specification
Frequency and PeriodSwitching frequency in kHz is converted to Hz, then period is calculated in microseconds.
Voltage ParametersInput voltage, diode drop, transistor drop and maximum VDS define turns ratio and flyback stress margin.
Core AL ValueAL in µH per turns squared is used to estimate required primary turns from primary inductance.
Output WindingsUp to four output voltage and current pairs can be included for total flyback output power.
Practical Operational Examples
Single Output Flyback
Use Vo1 and Io1 for one isolated output. Leave optional outputs as 0 if unused.
Multi Output Supply
Add Vo2 to Vo4 and Io2 to Io4 when designing auxiliary or multiple isolated secondary windings.
SMPS Transformer Check
Use primary inductance, turns and peak current results to compare with ferrite core and winding limits.
Repair Reference
Useful for checking approximate turns ratio and winding behavior in offline or DC flyback power supplies.
Diagrams & Theory
A flyback converter stores energy in the transformer primary during switch on-time, then transfers energy to the secondary side through the diode when the switch turns off.
Formulas & Mathematical Logic
Output power: Po = (Vo + Vd) × Io
Input power: Pin = total output power / efficiency
Original turns ratio: Nps1 = (Vdsmax × 0.8 - Vin) / (Vo2 + Vd)
Dead time: Tdt = T × 0.2
Charge time: Tch = (Vo1 + Vd) × Nps1 × (T - Tdt) / ((Vin - Vtran) + (Vo1 + Vd) × Nps1)
Primary inductance: L = ((Vin × Tch) × (Vin × Tch)) / (2.5 × T × Pin)
Primary turns: Np = sqrt(L / AL)
Primary current: Ip = Vin × Tch / L
Step-by-Step Example
Example: Frequency = 65 kHz, Vin = 24 V, efficiency = 80%, diode drop = 0.7 V, transistor drop = 1 V, VDS max = 150 V, AL = 100 µH.
Step 1: Convert frequency from kHz to Hz and calculate switching period.
Step 2: Calculate output power for each enabled secondary winding.
Step 3: Add all output powers and divide by efficiency to estimate input power.
Step 4: Calculate turns ratio, charge time, discharge time and dead time.
Step 5: Calculate primary inductance, primary turns, secondary turns, peak current and RMS current.
How to Use This Calculator
Enter switching frequency, diode drop, transistor drop, efficiency, VDS max, AL value and input voltage.
Enter output winding 1 voltage and current. This output is required.
For extra outputs, enter Vo2 to Vo4 and Io2 to Io4. Keep unused outputs as 0.
Click Calculate to get periods, powers, turns, inductance and current estimates.
Use the result as an early flyback transformer design estimate, then verify with datasheets and real testing.
About This Calculator
Estimate flyback transformer winding and power supply design values.
The CalcBoy Flyback Transformer Power Supply Design Calculator estimates switching period, output power, input power, turns ratio, primary inductance, turns, peak current and RMS current.
Flyback converters are widely used in isolated SMPS designs, auxiliary supplies, offline adapters, LED drivers, battery chargers and compact DC-DC converters. Unlike a normal transformer, a flyback transformer stores energy in the primary inductance during switch on-time and releases that energy to the secondary winding when the switch turns off.
This calculator helps with early transformer planning by combining switching frequency, input voltage, output winding values, diode drop, transistor drop, efficiency and core AL value. It can estimate primary turns, secondary turns, primary inductance, peak current and RMS current so you can compare the design with ferrite core limits, wire size and switching device stress.
Flyback design is sensitive to real transformer construction, leakage inductance, core saturation, snubber design, air gap, diode recovery, MOSFET rating, insulation safety and PCB layout. Use this as a design starting point only. Final SMPS designs must be checked with oscilloscope testing, thermal testing, creepage/clearance rules and component datasheets.
Best UseEarly flyback transformer and SMPS winding estimates.
Supported OutputsTurns ratio, inductance, winding turns, current and power values.
Helpful ForDC-DC flyback, auxiliary SMPS, isolated power supplies and ferrite transformer checks.
Design ReminderAlways verify saturation, leakage, thermal rise and safety isolation.
Tip: In real flyback supplies, leakage inductance and snubber design can decide MOSFET survival. Never rely on winding calculations alone.
Frequently Asked Questions
What does this flyback calculator estimate?
It estimates flyback switching period, output power, input power, turns ratio, charge/discharge time, primary inductance, turns and current values.
Can I use this for multi-output flyback transformers?
Yes. The calculator includes up to four secondary output voltage and current entries.
What is AL value?
AL is the core inductance factor, usually given in µH per turns squared. It helps estimate primary turns from required inductance.
Is this enough to build a safe mains SMPS?
No. Mains SMPS design requires isolation, creepage, clearance, protection, thermal testing and safety standards.
Why are peak and RMS current important?
They help check MOSFET stress, winding heating, wire size, core saturation and current sense design.
Should I test the final flyback supply?
Yes. Always verify waveforms, MOSFET drain voltage, transformer temperature, output ripple and load behavior on real hardware.
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