Flyback Transformers - Kickback Transformers

The single ended flyback circuit topology is a simple and low cost power supply. The flyback transformer utilizes the flyback, or kickback, action of an inductor or flyback transformer to convert the input voltage and current to the desired output voltage and current.


Figures 1A and 1B show simple flyback transformer schematics for an inductor and a flyback transformer.

These schematics do not show any parasitic effects, such as leakage inductance and winding capacitance. Modern flyback transformer and circuit design now permit use in excess of 300 watts of power, but most applications are less than 50 watts.

By definition a transformer directly couples energy from one winding to another winding. A flyback transformer does not act as a true transformer. A flyback transformer first stores energy received from the input power supply (charging portion of a cycle) and then transfers energy (discharge portion of a cycle) to the output, usually a storage capacitor with a load connected across its terminals. An application in which a complete discharge is followed by a short period of inactivity (known as idle time) is defined to be operating in a discontinuous mode. An application in which a partial discharge is followed by charging is defined to be operating in the continuous mode. See figures 2A and 2B for illustration.

Gapped core structures increase the magnetizing force needed to reach saturation and lower the inductance of the flyback transformer (or inductor). Consequently, a gapped flyback transformer (or inductor) can handle higher peak current values, and thereby storing more energy, most of which is stored in the magnetic field of the gap. For these reasons almost all flyback transformers (or inductors) are gapped. The gap may be a discrete physical gap, several smaller discrete physical gaps or a distributed gap. Distributed gaps are inherently present in low permeability powdered cores. The bulk of the stored energy is stored in the magnetic field of the gap(s). Most modern flyback transformers are operated at high frequency hence gapped ferrite core materials are typically used.

Butler winding can make (and has made) flyback transformers in a wide variety of shapes and sizes. This includes; various standard types of core with bobbin structures (E, EP, EFD, EC, ETD, PQ, POT, U and others), toroids, and some custom designs. We have experience with foil windings, litz wire windings, and perfect layering. For toroids, we can (and have done) sector winding, progressive winding, bank winding, and progressive bank winding. Butler winding has a variety of winding machines, bobbin/tube and toroid. That includes two programmable automated machines and a taping machine for toroids. To ensure quality, Butler Winding purchased two programmable automated testing machines. Most of our production is 100% tested on these machines.

If you need assistance with your design, please contact Butler Winding and ask for Engineering.