First fully integrated AC-DC active clamp flyback controller

March 19, 2019 //By Nick Flaherty
First fully integrated AC-DC active clamp flyback controller
Silanna Semiconductor has launched what it believes to be the world’s first fully integrated active clamp flyback (ACF) controller for high-power-density AC/DC power adapters.

The SZ1101 Flyback PWM Controller integrates four key ACF controller building blocks. These include an advanced ACF controller and three ultra-high-voltage components; an active clamp driver, an active clamp FET and a startup voltage regulator. This is aimed at adapters with low bill-of-material cost for mobile phones, tablets, notebooks and video game consoles.

Thermal constraints are limiting AC-DC converter design. For example, delivering 30W today without increasing the volume beyond the 2.4 cubic inch adapter that delivered only 15W a few years ago requires a minimum of 93.2% efficiency to ensure that the case stays under the desired limit of 50 degrees Celsius when operating at room temperature.

The SZ1101 delivers over 93% efficiency at 9V/3A with an all silicon design, and over 15W/in 3 power density at 30W while using an industry standard silicon MOSFET main switch. It uses an integrated ACF circuit, overcoming the traditional complexities of designing with ACF controllers. It does not require a tight tolerance for the clamp capacitor and leakage inductance, and Silanna’s proprietary OptiMode advanced adaptive digital control precisely controls the critical on/off timing of the active clamp FET based on system operating conditions. In an SZ1101-based power supply, designers get the benefits of an ACF controller with the design simplicity of a traditional flyback controller.

An SZ1101-based power supply replaces the conventional RCD snubber with a clamp capacitor and an integrated active clamp MOSFET for loss-less recycling of leakage energy to the output. Moreover, the SZ1101 utilizes proprietary techniques for precise control of the active clamp circuit to achieve near zero voltage switching (ZVS) to further improve efficiency. The device utilizes additional proprietary techniques to ensure optimal valley mode switching, tight switching frequency control and intelligent switching frequency handling to enable designers to achieve higher efficiency, reduced main switch voltage rating and appreciable attenuation of common-mode EMI noise.

Additionally, the SZ1101 reduces bill-of-material cost not only by integrating the ACF circuit, but also by


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