Tape Wound Toroidal Transformers
Tape wound core toroidal transformers are made by wrapping thin long strips of magnetic material around a winding mandrel. Originally, tape wound core toroids were developed to replace vacuum tubes. Vacuum tubes were fragile and required frequent replacement. The tape wound core toroidal transformers were more reliable. Magnetic coupling permitted the mixing of signals while maintaining electrical isolation between circuits. Tape wound core toroidal transformers also developed along another path. Early toroidal transformers used thin ring shaped laminations stamped from electrical steel. The steel from the center was waste material. A core was made by stacking these rings to the desired height. The laminated stack reduced core eddy currents. Lower eddy currents result in lower core losses. The thinner the laminations, the lower the losses were, but the more time it took to process and stack the laminations. Designers adapted the tape wound core process to general-purpose transformers as well. Winding tape wound core toroidal transformers were much faster than stacking toroidal cores; hence use of thinner material became more practical. The process was then adapted to rectangular cores known as C cores.
Today, tape wound core toroidal transformers can be made with strip as thin as 0.000125 inches. They are available in alloys of silicon steel, nickel-iron, cobalt-iron, and amorphous metals. Some materials are processed to enhance square loop properties. With appropriate gauss derating, the thin strip extends the useful frequency range up to 10 to 20 kilohertz depending on the type of material. Ferrite cores have lower core losses and cost less per unit weight, but their saturation levels are much lower. Low weight and minimal space are desired features for aviation and aerospace applications. Consequently tape wound core toroids are usually preferred over ferrites for these applications provided the operating frequency is not too high.
Tape wound core toroids wound with nickel-iron alloys are particularly sensitive to shock and vibration. These cores need to be place in a protective box with a damping medium such as silicon oil. Silicon steel alloys are the least sensitive. Silicon steel is frequently used without a protective box. It depends on the particular application.