Friday, October 14, 2016

High Efficiency Step Down Isolated Supply

60W AC-DC adapter, synchronous rectification, fixed frequency current mode PWM controller. Very Low Quiescent Burden, Efficiency above 85%. That's Green.

STMicroelectronics - EVALSTSR30-60W. Synchronous rectification using L6668 and STSR30.

EVALSTSR30-60W: 60W AC-DC adapter
EVALSTSR30-60W: 60W AC-DC adapter

The converter works in both Continuous and Discontinuous conduction mode depending on the input voltage (the circuit has a wide input voltage range) and the output load. The 68-kHz switching frequency provides a good compromise between the transformer size and the harmonics of the switching frequency, optimizing input filter.

High Efficiency Step Down Isolated Supply

The input section includes protection elements (varistor, fuse and NTC for inrush current limiting), a standard Pi-filter for EMC suppression, a bridge and an electrolytic bulk capacitor as the front-end AC-DC converter. The transformer is a layer type, uses a standard ETD34 ferrite core and is designed to have a reflected voltage of 95V. The power MOS is a 700V - 1Ω and a transil clamp network is used for leakage inductance demagnetization.

From STMicroelectronics