Abstract: A low dissipation shunt or series regulator apparatus is described comprising dump switching means coupled in parallel to each power source, which dump switching means is arranged for being responsive to a control signal produced by comparator means arranged for comparing the level of the error signal with a respective reference level. Each power source has its output connected to the reference level input of the corresponding comparator through feedback circuit means in order to set two operation thresholds for the comparator, thereby allowing each dump switching means to switch cyclically between two states, a first state serving to short the corresponding power source and a second state serving to allow the power source to provide current to the load.