Integrated 60W active clamp flyback controller cuts AC-DC size

April 15, 2019 //By Nick Flaherty
The SZ1105 Flyback PWM controller combines four key elements. These are an advanced adaptive digital ACF controller, an active clamp MOSFET, an active clamp FET driver and a startup voltage regulator.
Silanna Semiconductor has launched a fully integrated 60W active clamp flyback (ACF) controller for smaller AC-DC power supply designs.

The SZ1105 Flyback PWM controller combines four key elements. These are an advanced adaptive digital ACF controller, an active clamp MOSFET, an active clamp FET driver and a startup voltage regulator.

The integration allows efficient, high-power-density AC-DC power adapters with low bill-of-material (BOM) cost for notebooks, video game consoles and multi-port wall chargers.

High-power-density capabilities help designers overcome the thermal challenges of packing ever-increasing amounts of power into the small-form-factor power adapters that consumers have come to expect that also remain cool to the touch. High efficiency, or reducing power loss, is key to achieving the power density without overheating the adapter’s case. With a simple flyback controller and an all-silicon design, the SZ1105 delivers over 93% efficiency at 20V/3A, and over 20W/in3 power density at full 60W output power. This is achieved with an industry-standard, avalanche-rated silicon MOSFET main switch.

The SZ1105 combines the design simplicity of traditional flyback AC-DC design with the efficiency and power density of ACF as the integrated circuit overcomes the traditional complexities of designing with ACF controllers. It eliminates the need for a tight tolerance for the clamp capacitor and leakage inductance. Instead, Silanna’s proprietary OptiMode adaptive digital control technology manages the critical on/off timing of the active clamp FET based on system operating conditions.

By replacing the traditional RCD snubber with a clamp capacitor and an integrated active clamp MOSFET, the SZ1105 delivers lossless recycling of leakage energy to the output. Precise control of the active clamp circuit delivers near-zero-voltage switching (ZVS) for further efficiency improvements. Additional features include optimal valley mode switching, tight switching frequency control, and intelligent switching frequency handling, all of which result in higher efficiency, a reduced main switch voltage rating, and appreciable attenuation of common-mode EMI noise.


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