Flyback Transformer: Construction and Working Principle

The flyback transformer is a special type of transformer, which can produce high voltage, high-frequency electric signals, that are generally saw-tooth signals. The flyback is also known as a line output transformer (LOPT). It is exclusively used in modern electronic applications like CRT displays, LED fixtures, solar micro-inverters, telecom, AC-DC power supply, and many more. Since this device is of great use in modern electronics, it is essential to better understand its design, its construction, its function, and its range of applications. Are you aware of all these factors? If you are not, then this post holds some of the answers. This post introduces you to flyback transformer design and construction, its working principle, and its significant industrial applications.

Flyback Transformers

An Overview of Flyback Transformer

The flyback transformer is an inductor featuring conductive coils called primary and secondary winding with an inductive gap in between. As the input voltage is applied to the primary winding, it generates energy which is first stored in the gap and then is transferred to the secondary winding. It works on the basis of flyback topology in which the energy generated is first stored in the form of a magnetic inductor and then is transferred to the secondary winding after switch is turned off. These flyback transformers are used as voltage converters or circuit isolators. Generally, the flyback transformer is the principle component in a flyback converter circuit and it is used in many applications.

Flyback Transformer Design/Construction

The flyback transformer is a special type of transformer, poses a slightly different design or construction layout. In order to give a better understanding of the flyback transformer, the flyback transformer design layout is discussed below.

  • At first, the primary coil is wound around a ferrite core. It generates the first portion of the inductor circuit.
  • Further, the secondary coil is wound around the same core as the primary winding. This links the two “inductors” magnetically. In some cases, the secondary winding is wound around the primary winding.  This is often done to minimize leakage inductance. Due to the high voltages involved, the secondary is typically built using a layering technique were the magnet wire is layered between insulators such as polyester film to offer higher dielectric strength for high voltage assemblies.
  • Finally, the ferrite core is assembled such that there is a gap in the magnetic flux loop. This gap helps increases magnetic reluctance and the magnetic field lines remain in the ferrite core.

However, this construction or design layout is traditional. It is further integrated with a primary switch, input capacitor, output capacitor, and output rectifiers in real-time industrial applications. The primary switch enables the flow of voltage through the primary winding, the input/output capacitors are attached to flyback transformer assembly in order to store electric current and the output rectifier smoothens the output before sending it to operational electronic equipment.

disc shaped AC flyback transformer

Working Principle of Flyback Transformer

In principle, the flyback transformer is connected to an integrated circuit with other electronic devices.  The real-time operation of a flyback transformer is detailed as follows.

  • In an integrated circuit, a flyback transformer is powered by turning on a primary switch. As the switch is turned on, voltage/current is passed through the primary winding.
  • As the current passes through the primary winding, primary power increases.
  • The generated power is stored in the form of magnetic energy in the inductive gap of the transformer. This energy storage takes place in accordance with flyback topology. The energy is stored in the gap until the primary switch is turned off.
  • The secondary winding is attached to a diode that allows the current to flow in one direction in the secondary circuit and blocks the current from flowing in the opposite direction. Therefore, once the primary switch is turned off, the secondary current flows through the diode and the energy stored in the gap is transferred to the load.

This completes one cycle of a flyback transformer. However, the cycle can be repeated after the secondary coil discharges the current to zero. If this happens and there is no stored current remaining in the gap then this is called discontinuous mode. If there is still some amount of current stored in the gap, then it is called continuous transformer mode.

Now that we have introduced the flyback transformer along with its design and working principle, it is important to acknowledge that the quality of the flyback transformer is just as important to its performance. Therefore, if you are looking to source a quality flyback transformer, please contact Custom Coils. The company has been a prominent supplier of various flyback transformers and inductors since 1967.


GT Stepp - Electrical Engineer with over 20 years of dedicated experience, proficient in the research, evaluation, test & support of various technologies. Devoted to success; comprising strong analytical, organizational & technical skill. Currently working as Sales & Operations Manager at Custom Coils, developing sales and marketing strategies that increase sales to make Custom Coils more recognized and respected in the marketplace.