Efficient Active Clamp Flyback (ACF) Controller For Power Adaptors

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The AC-DC controller delivers BOM savings in high power density universal input 65W and PFC-supported 100W adaptors

 

To reduce the operational and no-load/ standby power consumption of high-efficiency chargers and adaptors while driving down component count, BOM cost and size, Silanna Semiconductor has launched a new integrated active clamp flyback (ACF) controller called the SZ1131 ACF controller. This addition to Silanna Semiconductor’s family of CO2 Smart Power technologies helps address power management challenges faced by engineers while simplifying design and improving performance for achieving environmental sustainability through more efficient energy use. 

In the case of the SZ1131, efficiencies of up to 95% across universal (90Vac – 265Vac) input voltages and varying loads, combined with ultra-low no-load power of less than 20mW (including USB-PD applications) significantly reduce overall energy consumption.

The new ACF controller is targeted at high efficiency and high power density adaptors of up to 65W output power with universal input and 100W output power with PFC-support applications, including single-port and multi-port USB-PD fast chargers. A high integration level allows the SZ1131 to incorporate an adaptive digital PWM controller, ultra-high-voltage (UHV) active clamp FET, active clamp gate driver and startup regulator.

The SZ1131 provides the ease-of-design of a simple flyback controller with all the benefits of an ACF design, including recycling the leakage inductance energy of the flyback transformer and limiting the primary FET drain voltage spike during the turn-off events. By employing Silanna’s proprietary OptiModeTM digital control architecture, the SZ1131 adjusts a device’s mode of operation on a cycle-by-cycle basis to maintain high efficiency, low EMI, fast dynamic load regulation and other key power supply parameters in response to varying line voltage and load.

An all-silicon 65W USB-PD reference design using the SZ1131 demonstrates a 30W/inch3 power density (uncased) with impressive ~93% low line (90Vac) and > 94% high line (230Vac) efficiencies while using lower-cost components. These include a conventional RM8 transformer, 100V SR FET, minimal clamp capacitor and a single common mode choke in the input filter. The company’s technology-agnostic approach focuses on the ultimate power management challenges and delivers higher efficiency and power density when paired with GaN primary FETs.

Key Features

  • Integrated UHV active clamp FET, active clamp driver and start-up regulator
  • Capable of over 95% efficiency
  • Flat efficiency across universal (90Vac to 265Vac) input voltage and load
  • < 20mW system no-load power consumption
  • OptiMode cycle-by-cycle adaptive digital control
  • Self-tuning valley mode switching (VMS)
  • Multi-mode operation (burst mode, QR, VMS)
  • > 6 dB EMI margin
  • OTP, OVP, OCP, OPP, output short circuit and transformer saturation protection
  • Up to 65W output power with universal input and 100W+ output power with front-end PFC
  • 16-pin SOIC package
  • CO2 Smart Power by Silanna Semiconductor 

Applications

  • High power density AC-DC power supplies
  • High-efficiency power adapters
  • USB-PD/QC AC-DC power adapters
  • Battery chargers for mobile devices

“This device sets a new benchmark for integration and further re-enforces Silanna’s commitment to combining performance and sustainability. Chargers for smartphones and laptops are often left plugged in, even if they are only charging for a few hours at a time. By focusing on extending efficiency margins against CoC, DoE and other regulatory requirements and driving down no-load power we allow customers to deliver best-in-industry efficiency under varying line, load and temperature conditions at the same time as minimising ‘vampire’ power,” said Mark Drucker, CEO, Silanna Semiconductor.

Supplied in a 16-pin SOIC package, the SZ1131 offers protection against over-temperature, over-voltage, over-current, over-power and short circuit conditions and transformer core saturation faults without the need for additional external components. SZ1131 devices are being sampled to key accounts and will be released for full production in Q4 2021.


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