Configurable ac/dc power supplies have medical approval

Paul Boughton

Former distributor XP has developed its first family configurable ac/dc power supplies that has been designed entirely in-house, with medical approval included for the first time.

XP Power now distributes all its own products, and the FleXPower family is the first product since the acquisition of Switch Signal International (SSI) in Anaheim, California, three years ago. Using the design team in Anaheim and its relationship with the Underwriters Labs (UL) approval house, the new range is pre-approved for all power output ranges, rather than having to qualify each individual product.
The ac/dc system is configurable from a universal input providing 400W to 900W at 3.3V to 60V with a high line option to bring the power output to 1100W. Two chassis together provide up to 2200W.
The company has made a number of innovations to the design, which uses modules on a 400V bus to provide a configurable output.
By reducing the number of PCBs from three to one with four layers, and using a thermal clad material to reduce the thermal resistance of the power transistors, the unit has been made one inch shorter and the MTBF has been doubled. This has also allowed more space to achieve the medical qualification. Removing the daughter cards has also improved the shock and vibration resistance, from 10G to 20 o 30G.
The fan has also been made quieter (again a demand from the medical market) and set on a removable board so that it can be replaced as part of a maintenance programme. This has increased the MTBF from 50000 hours to over 200000 hours, says Gary Bocock, European technical director.
The design has been optimised for fast configuring in the factory, with access to the unit from the bottom without taking the top off, for example to turn the fan around to reverse the airflow.
The new design also replaces its snubber with a single silicon carbide diode from Cree that provides 1percent better efficiency and is the same cost as the existing seven components in the snubber. That SiC diode is now being used across the whole range of XP suppliers, he says. The metal oxide varistors and gas tubes have also been removed.
An electrically floating heatsink provides better EMI protection by reducing the differential voltage, and lower leakage current, he says.
What fleXPower does not add is direct digital control. It has an interface for an I2C or CAN bus, but XP has not added microcontrollers for the main control loop, which is more suited for point of load applications.

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