US Patent 7755862 Apparatus for writing a magnetic layer

An apparatus for writing a magnetic layer writable with either low or high coercive field strength includes a magnetic head having a magnet coil and a voltage source. The apparatus includes switches between the voltage source and opposing ends of the magnet coil. Two further switches serve to maintain the direction of current flow through the magnet coil. A current measuring device determines the current intensity through the magnet coil. The current measuring device drives the switches in such a way that the current intensity in the magnet coil does not exceed or undershoot a level required for writing the magnetic layer.