  The increase in the number of readout channels in new detectors, like the
Micro Pattern Gas Detectors (MPGD), in the order of several millions, requires
a large amount of electrical power to supply the front-end electronics, up to
hundreds kW. If this power is generated at long distances from the detector,
the voltage drop on the connection cables puts serious constraints to the
supply current, to the wire cross-section and to the power distribution. A
large amount of voltage drop on the cables, apart an increased power
dissipation on wire resistance, determines regulation issues on the load in
case of current transients. To mitigate these problems, a new generation DC/DC
converter, working in a heavily hostile environment and with a power density
greater than 200 W/dm3, was developed. It is modular, with up to four
independent modules, eight channels each, collected in a water-cooled crate,
and can supply the load with an adjustable 10 to 12 V output up to 170 W per
channel. In this contribution, the design constraints of such a converter are
analysed, taking as a basis the environmental, electrical and mechanical
requirements of the ATLAS New Small Wheel (NSW) project. Thermal considerations
require the converter to be water-cooled, and the dimensional constraints
impose the adoption of an innovative design to convey the dissipated heat
towards the heat exchanger. The control and monitoring system allows for the
full remote management of the converter. Main electrical parameters were
measured and are reported. The converter was also characterized in a harsh
working environment, with radiation tests in the CERN CHARM facility beyond the
limits estimated for ten years operation in ATLAS, and with magnetic field
tests in various orientations, using different magnets at CERN up to 1.3 T.
