What Is the Flyback Converter DCM Magnetizing Design Calculator?
A Flyback transformer is actually a coupled inductor that stores magnetic energy during switch ON time and releases it into the secondary circuit during switch OFF time.
In Discontinuous Conduction Mode (DCM), the secondary current drops to zero before the next switching cycle begins, eliminating secondary diode reverse recovery losses.
How Does the Flyback Converter DCM Magnetizing Design Calculator Work?
Input power Pin = Pout / efficiency accounts for internal copper, core, and semiconductor switching losses.
Peak primary current is derived from the triangular energy storage profile.
Primary inductance Lp is calculated to store precisely the required energy 0.5 * Lp * Ipk^2 each switching cycle.
Reflected primary voltage Vor sets the turns ratio Np/Ns to ensure complete core demagnetization.
Flyback Converter DCM Magnetizing Design Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Calculates peak primary switch current, critical primary inductance, and transformer turns ratio in DCM.
How to Use the Flyback Converter DCM Magnetizing Design Calculator
- Specify minimum DC input voltage (e.g., 100V for universal 85-265 VAC rectified mains).
- Enter regulated DC output voltage and power demand.
- Choose switching frequency and allowable maximum duty cycle.
Step-by-Step Example Calculation
Flyback DCM Design Standard Case
Input Values:
Understanding Your Result
Primary inductance Lp defines the transformer gapped core inductance index AL.
Peak switch current determines the current rating of the primary MOSFET and current-sense resistor.
Reflected voltage Vor + Vin_max determines the minimum breakdown voltage rating (BVDSS) for the MOSFET (plus leakage spike margin).
Factors That Affect the Result
- Switching frequency: Doubling frequency cuts required transformer core size in half.
- Duty cycle: Lower Dmax increases peak currents but gives more time for secondary demagnetization.
- Leakage inductance: Primary-to-secondary leakage inductance creates high-voltage turn-off spikes requiring RCD snubber clamps.
When Should You Use This Calculator?
- Designing USB-C power delivery adapters, auxiliary industrial power supplies, and LED lighting drivers.
- Specifying custom EE or RM ferrite core winding turns and air gaps.
Assumptions & Limitations
- Assumes pure DCM operation at full load; higher loads or higher input voltages may transition into quasi-resonant (QR) or CCM modes.
- Assumes 0.7V forward drop for secondary Schottky rectifier diode.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard energy conservation formulation for discontinuous flyback coupled inductors.