  SPIDER, the ion source prototype for ITER neutral beam injectors, has been in
operation since 2018. The experiment includes a system of Ion Source and
Extraction Power Supplies (ISEPS), whose design dates back to 2011. Since then
the experience gained has led to substantial changes, the most dramatic
modification being the complete replacement of the radiofrequency power supply,
described elsewhere. This contribution details operating experience and
calculations that have led to defining new requirements for a specific subset
of power supplies, the bias power supplies. The bias power supplies perform the
function of filtering out electrons extracted together with the negative ions
and in the original 2011 ISEPS design are single quadrant resonant converters.
For the two bias power supplies, the picture resulting from the review
described in the paper is a substantial redesign, with the ability to operate
in four quadrants and a twofold increase of the rated output voltage the most
significant new specifications.
