This Design Idea is a two-wire current regulator that strikes a good balance between performance and parts count, and can deal with low voltage and medium to high currents.

Correction: Corrigendum: Hybrid single-electron transistor as a source of quantized electric current Jukka P. Pekola, Juha J. Vartiainen, Mikko Möttönen, Olli-Pentti Saira, Matthias Meschke & ...