An electronic resonant circuit of very high efficiency which is suitable for driving loads with a known and controlled current. The resonant circuit has input terminals and output terminals with a first reactance Xs, in series with an input terminal, a second reactance XL, in series with an output terminal, and a reactance Xp, connected such that there is a series connection path between the first input terminal through Xs and Xp to the second input terminal and such that there is also a second series connection path between the first output terminal through XL and Xp to the second output terminal the input terminals being driven from a high frequency inverter, the output terminals being connected to a load, the value of the reactances Xs, XL and Xp being chosen such that at least one frequency, the reactances of Xs, XL and Xp are approximately similar in magnitude. The reactance Xs and second reactance XL, are predominantly capacitive over a wide range of the frequency of operation and the reactance Xp, is predominantly inductive over a wide range of the frequency of operation. The circuit according to this invention is particularly suited to driving LED lighting systems, constant torque motors, battery charging and capacitor charging.