FROM EDN EUROPE: Configurable supply reaches for new efficiency levels
By Graham Prophet -- EDN, June 10, 2004
In the search for ever-higher efficiencies in the power-conversion chain, Lambda has turned its attention to the ac/dc (offline) multiple-output power supply (Picture). With the introduction of the NV series, the vendor uses a new topology with reduced switching losses. As efficiencies rise to 90% and above, companies are making incremental gains by paying attention to the fine detail of tracking the energy through every part of the switching cycle; the NV is no exception. It uses a topology based on synchronous rectification in a resonant mode. Previous configurable Lambda products used a magnetic-amplifier-based architecture and were configurable by adding discrete secondary windings to the main isolation transformer. This series, however, is structured as an ac/dc converter (to 400V) configurable by adding dc/dc converters as required.
First units in the range have 175 and 300W; a modular 600W unit will follow. For compatibility with 1U rack-mount applications, the units measure 95 mm high. The design uses reduced-value inductors for lower losses, multilayer ceramic capacitors in inductor-less filters, and silicon-carbide diodes in the power-factor-correction input stage, all leading to increased efficiency. Other gains the vendor claims for the design are reduced cooling requirements (the 350W unit has small twin fans, and the 175W device has an open frame and is ambient-cooled), lower EMI, and preapproval for medical-equipment standards. You can specify up to three single- or dual-output modules on the 350W version, spanning 3.3 to 32V, with 2 to 40A output-current ratings. The nonconfigurable, open-frame supply can provide as many as five outputs from 0.9 to 15V, 1 to 25A, with all outputs regulated. You cool it with forced airflow, and you can derate it to fully convection-cooled. Resulting overall energy densities are 6.6 and 9.36W/in3, respectively, for the two supplies.
Lambda, +44 1271 856666, www.lambda-europe.com.
