New Industry Products

Silanna Unveils First Fully Integrated Active Clamp Flyback Controller

March 17, 2019 by Paul Shepard

Silanna Semiconductor today unveiled the world's first fully integrated active clamp flyback (ACF) controller with adaptive digital control for designing high-power-density ac-dc power adapters. Silanna's SZ1101 Flyback PWM Controller is being introduced to the industry at the IEEE Applied Power Electronics Conference in Anaheim, CA (booth #860). The SZ1101 integrates the 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 (see above schematic).

This unprecedented level of integration facilitates designing efficient, high-power-density adapters with low bill-of-material cost to satisfy power-hungry mobile phones, tablets, notebooks and video game consoles.

To support the ever-increasing energy and fast charging needs of mobile devices, designers today are challenged to deliver increasing amounts of power in a travel adapter while also keeping it cool to the touch and maintaining the small size consumers have come to expect. High efficiency, or reducing power loss, is key to achieving the power density without overheating the adapter's case.

For example, delivering 30W today without increasing the volume beyond the 2.4 cu-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/in3 power density at 30W while using an industry standard silicon MOSFET main switch.

Combining Flyback Simplicity with the Efficiency and Power Density of ACF

The SZ1101, with its integrated ACF circuit, overcomes 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 enabling designers to use a lower cost transformer, SR FET, clamp capacitor and input filter compared to conventional ACF or flyback-controller-based designs.

"With its ease-of-use and many other benefits for the power supply designer, we anticipate the SZ1101 will be a disruptive force in the industry," said Zahid Rahim, vice president of marketing, Silanna Semiconductor.

(click on efficiency curves to enlarge)

SZ1101-based ac-dc power supplies easily meet the stringent DoE and CoC efficiency and no-load standby power requirements.

Key Specifications:

  • Input: 90- to 265-Vac
  • Output: 3.3V, 5V, 9V, 11V, 12V, 15V, 20V
  • Output Current: 3A Max
  • Output Power: 30W Max
  • Output Port: USB-PD 3.0 or PPS
  • Efficiency: > 93% full power efficiency with an all silicon design

Key Features:

  • Integrated ultra-high-voltage active clamp FET/ driver/ startup voltage regulator
  • Advanced adaptive digital control
  • Tight switching frequency regulation for improved input EMI filter utilization
  • Cycle-by-cycle adaptive digital control (OptiMode™)
  • Up to 30W output power
  • Capable of over 15W/in3 power density
  • SO-16 package


Featuring the industry standard 16-pin SOIC package, a latched version (SZ1101-01) is available immediately for sampling, and a hiccup mode version will be available in Q2. 10K pricing is to be determined.