Active clamp fly-back controller for adapters up to 100W

Called SZ1131, it has an integrated clamp mosfet and a driver for an external fly-back mosfet.

Efficiencies up to 95% across 90 – 265Vac input voltages and varying loads are possible, according to the company. No-load power can be as little as 20mW, including in USB Power Delivery (USB-PD) applications.

65W can be delivered from a universal input, and 100W output power with PFC-support.

Active clamp fly-back controller for adapters up to 100WApplication circuit (preliminary)

“SZ1131 provides the ease-of-design of a simple fly-back controller with all the benefits of an ACF design, including recycling the leakage inductance energy of the fly-back transformer and limiting the primary FET drain voltage spike during the turn-off events,” according to the company. Using its digital control architecture “SZ1131 adjusts the device’s mode of operation on a cycle-by-cycle basis to maintain high efficiency, low EMI and fast dynamic load regulation.”

An all-silicon 65W USB-PD example design is available that achieves 30W/in3 (uncased), ~93% low line (90Vac) efficiency and >94% high line (230Vac). It includes a conventional RM8 transformer, 100V synchronous rectifier fet, clamp capacitor, and single common mode choke input filter. It “delivers even higher efficiency and power density when paired with GaN primary FETs,” said Silanna.

Supplied in a 16pin SOIC package, protections include over-temperature, over-voltage, over-current, over-power, short-circuit and transformer core saturation without additional external components.

Parts are sampling now, with full production planned in Q4 2021.

The SZ1131 product page is here

Silanna Semiconductor’s HQ is in San Diego.