Abstract: A circuit for charging an electrical storage device, such as a capacitor, from a source of energy via an induction coil interconnected between the source of energy and the storage device. Current from the source of energy builds up a magnetic field within a primary winding of the coil. A sensing circuit detects a desired maximum value of the magnetic field and then operates a switch to disconnect the primary winding from the source of energy. As the magnetic field starts to collapse, a voltage induced in a secondary winding of the coil enables energy stored in the magnetic field to be transferred to the storage device. When a given minimum value of the collapsing magnetic field is then reached, the primary of the induction coil is reconnected to the source of energy to repeat the above cycle. The minimum of the magnetic field is relatively close to the desired maximum, to permit only a partial magnetic field drop before commencing the next cycle.