Flyback transformers are a key component in switched-mode power supplies (SMPS), used for their ability to provide electrical isolation and convert voltages efficiently. Unlike traditional transformers, flyback transformers store energy in the magnetic field during the switch “on” time and release it during the “off” time. This operation allows them to serve as both an inductor and a transformer.

Key Construction Features:

Magnetic Core with Air Gap:

A gapped ferrite core (often EE or EC core shapes) is used to store energy and prevent core saturation.

The air gap is precisely calculated based on energy requirements per switching cycle.

Winding Configuration:

Primary winding connects to a high-frequency switching element (MOSFET, IGBT).

Secondary winding(s) are coupled magnetically and isolated electrically, providing one or more outputs.

Proper winding techniques (e.g., interleaving, shielding) are applied to reduce leakage inductance and improve coupling.

Insulation & Isolation:

Designed for compliance with UL and IEC insulation standards.

Isolation voltage levels are customized per design for safety-critical applications.

Bobbin & Wire Materials:

Thermally rated bobbins (UL94V-0) and enameled copper wire of appropriate gauges ensure durability and performance under high-frequency operation.

🔌 Connection & Operation
Basic Flyback Circuit Connection:

Input Side:

The primary winding is connected to the input voltage via a switching transistor.

Switching:

When the switch turns ON, current builds in the primary and energy is stored in the core.

When the switch turns OFF, the collapsing magnetic field induces voltage in the secondary.

Output Side:

The secondary winding delivers the output through a fast-recovery diode and output capacitor.

Energy is transferred only during the switch-off phase, unlike forward transformers.

⚙️ Modes of Operation
Discontinuous Conduction Mode (DCM):

Energy is fully discharged before the next cycle begins.

Results in simpler control loops, lower cost, smaller transformer size.

Common in lower-power and cost-optimized applications.

Continuous Conduction Mode (CCM):

Some energy remains in the core between cycles.

Reduces peak currents and EMI but requires more complex feedback control.

Used in higher-power designs.

🔧 Custom Design Capabilities
If you need a flyback transformer with specific electrical, mechanical, or environmental requirements, CET Technology can help.