This circuit with a few watts of power was found in the April 1995 issue of Electronics Now magazine. The voltage obtained and the efficiency depend greatly on the transformer.
This setting appears elsewhere in this site from other sources or projects. Instead of the lamp...
In the figure we have the way to obtain an adjustable constant current source of 2 mA. The...
This circuit was obtained from an American publication of 1982, but can be easily assembled today...