An intrinsically safe power supply for conditioning power or current has an input power or current transformer with three devices to limit the power drawn and a fourth device for switching off the power source in the case of an external disturbance plus a fifth device for limiting the energy stored in the output filter. The first of the limiting devices is a switch connected between the input transformer and output filter which conducts current through a low impedance path. The second and third devices are series impedances in the output circuit. The fourth device is an adaptive non-linear spark discriminator circuit detecting changes in the output current and the fifth device is a multi-stage LC filter.
