An LED light source powered by an unstable three-phase AC network is described and relates to lighting technology and is intended for use in LED lighting devices which run on unstable three-phase AC networks. The technical and economic results of the claimed invention are a significant reduction in the cost, an increase in the reliability and a reduction in the weight and dimensions of LED lighting drivers, as well as an increase in the efficiency thereof. An LED-based light source includes a three-phase voltage rectifier (a first voltage source), a second adaptive voltage source, a voltage sensor of the first voltage source, and a group of series-connected LEDs with a passive current source, the first and second voltage sources being matched and connected in series, and the group of LEDs, connected in series with a passive current source, being connected into their combined voltage, wherein the voltage of the adaptive (second) voltage source is controlled by the voltage sensor of the first voltage source such that the combined voltage of the two voltage sources is always constant and depends on the range of instability of an AC network and the voltage at the adaptive voltage source.