Flyback Converter Calculator

A flyback converter is a buck-boost DC-DC converter that provides galvanic isolation between input and output using a transformer. It can step up or step down voltage while maintaining electrical isolation between circuits.

When the switching transistor turns on, energy is stored in the primary winding magnetic field. When it turns off, this stored energy transfers to the secondary winding and powers the load. Energy transfer occurs during the off-time, unlike forward converters.

Flyback converters have higher voltage stress on the switching transistor, limited power capability (typically under 120W), and higher output ripple compared to forward converters. They also require careful transformer design for proper operation.

A flyback transformer is actually a coupled inductor with an air gap that stores energy in its magnetic field. It provides voltage transformation, galvanic isolation, and energy storage functions in the converter circuit.

The flyback voltage depends on the turns ratio and output voltage. The primary side sees the reflected output voltage multiplied by the turns ratio, plus the input voltage, which determines the MOSFET voltage stress.

Flyback converters are typically used for power levels up to 120W due to their energy storage mechanism and voltage stress limitations. For higher power applications, forward or other topologies are preferred.

Higher frequencies allow smaller transformers but increase switching losses. Typical frequencies range from 50kHz to 500kHz. Consider EMI requirements, efficiency targets, and component availability when selecting frequency.

The air gap prevents core saturation and provides the energy storage capability. It linearizes the inductance and allows the core to store energy in the magnetic field, which is essential for flyback operation.