Silanna Touts Efficiency and Ease of Design with World’s First Active Clamp Flyback Controller

March 20, 2019 by Baker Lawley

Silanna announces an active clamp flyback controller with built-in UHV components for AC/DC power adapters.

At APEC this week, Silanna announced an active clamp flyback (ACF) controller with integrated UHV components for AC/DC power adapters.

Power adapters used to charge our mobile devices have growing power demands as devices consume more energy. Yet the power adapters themselves must remain both small and cool in temperature, so adapters have to negotiate conflicting demands.

One reason the small size is a challenge is because of the FET in power adapters. The faster the switching frequency, the smaller the power adapter can be. However, faster switching brings with it more leakage, and if that leakage is stored it can generate enough heat to burn the adapter up. 

What is Active Clamp Flyback?

Flyback controllers are often used to capture leakage and store it, but this is taken another step when the flyback controller is active.

Active clamp flyback is a method of harnessing the leakage energy from the transformer generated by the switching frequency. The active clamp flyback increases efficiency by intelligently sending the stored leakage energy through the output in a controlled pattern later in the cycle. This allows the FET to switch at higher frequencies, reducing the necessary size of the power supply. 

The SZ1101 Addresses Active Clamp Flyback with Integration

At APEC this week, AAC met with Zahid Rahim, VP of Marketing at Silanna Semiconductor, about the SZ1101. Silanna claims the SZ1101 to be the world's first fully-integrated active clamp flyback controller. In a typical AC-DC power supply, you have a flyback controller, but the active clamp flyback controller requires a few more components.


The front and back of the SZ1101 PCB. Image courtesy Silanna.


"In an active clamp flyback design, you need an active clamp MOSFET, a high-voltage driver for that active clamp MOSFET, and you need a high-voltage startup circuit. And then, of course, you need a flyback controller," Rahim states. "So in the SZ1101, all four of those components are integrated in the IC. As a user, you get the benefit of active clamp flyback which gives you a higher efficiency. And you get the simplicity of design of a flyback control."


SZ1101 schematic. Image courtesy Silanna.


Integrating the flyback with the three UHV components allows a simpler setup that has many performance advantages. The platform is 93% efficient, and is built on an all-silicon design which gives it a low BOM. Further, as an IC, the product has a lifetime reliability of millions of hours. 

"With our solution, [designers] can enjoy the benefits of active clamp flyback with that ease of the design of a flyback controller. That is a disruption in the market," notes Rahim.

Silanna has a 30W product available now with 15W/in3 power density, and they will be releasing a 60W product next quarter. 

Key Features:

  • Integrated ultra-high-voltage active clamp FET/ driver/startup voltage regulator
  • Advanced adaptive digital controller 
  • Tight switching frequency regulation for improved input EMI filter utilization
  • Up to 140kHz switching frequency
  • Cycle-by-cycle adaptive digital control (OptiMode   )
  • Up to 30W output power
  • Capable of over 15W/in  power density 
  • 16-pin SOIC package


Key Specs:

  • Input: 90 – 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

Featured image courtesy Silanna.

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