AHB Flyback AC-DC Power Circuit Design

Asymmetric Half-Bridge Flyback Circuit Overview:

The Asymmetric Half-Bridge Flyback (AHB) is a soft-switching isolated power conversion topology. It combines the low stress of the half-bridge topology with the simplicity of the flyback, using transformer leakage/magnetizing inductance and a resonant capacitor to achieve ZVS for the primary-side switches, while recovering the leakage energy that is normally lost in a traditional flyback converter. It is therefore well suited to high-efficiency, high-power-density low-to-medium power applications (adapters, automotive power, server auxiliary supplies, etc.).

Detailed design of the 100~240W AC-DC AHB flyback circuit

Key Input/Output Specifications:

Input voltage: AC100V~AC240V

Power factor

0.99

Output power

max 240W

Output voltage

this example 20-48V, regulation accuracy ±1%

Output current

this example 3-5A, current accuracy ±10%

Power efficiency

94% @AC220V input, 20V 7A output

Overall Circuit Scheme

This design adopts an integrated "PFC + AHB asymmetric half-bridge" + synchronous rectification architecture. The front-end PFC stage uses the PFC-specific integrated chip DK8318 with built-in GaN FET switch, operating in highly efficient critical conduction mode (CrM) to achieve a power factor as high as 0.99. The main power conversion stage uses the DK8515 with dual integrated GaN FETs to implement the AHB (asymmetric half-bridge) topology, which achieves ZVS for the primary switches via resonance, effectively reducing switching losses. On the output side, the KP4060LGA high-performance synchronous rectifier controller replaces traditional Schottky rectifier diodes, minimizing secondary rectification loss and significantly boosting overall efficiency.

1. Circuit Schematic

Key components BOM list: