Introduction To Flyback Transformer

By Ashwini Kumar Sinha

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As you all are aware, the transformer is an electric device that converts high voltage to low voltage and vice versa using mutual induction.

A flyback transformer is a special type of step-up transformer that generates high voltage signals and has a huge potential boosting capacity. Picture tubes and CRT television are some application examples where a flyback transformer is used.

With an input of 230 V, these transformers can provide an output of around 20,000 V. They can even operate at voltages as low as 12 V to 5V.

Design of Flyback Transformer

It consists of a small number of electrical components. A switching device consisting of transistors or MOSFETs is present at the input to cut-on and cut-off the input voltage of the primary coil. The secondary coil has a diode that restricts the current flow in reverse bias.

Construction of Flyback transformer
Fig 1. Construction of Flyback transformer

Unlike normal transformers, a flyback transformer is designed in such a way that it can be excited using DC voltage. The primary winding is driven by a switch using DC supply. When the primary coil gets energised, the magnetic flux is transferred to the secondary coil. But since the secondary coil is connected to a diode in reverse bias, the current gets stored. Therefore the next incoming pulse from the primary winding adds on this stored current (i.e the energy stored in the previous pulse). This subsequent addition results in a very high pulse of electricity at the output.

Principle of Flyback Transformer

A flyback transformer works by storing energy in the form of a magnetic field during the first half-cycle and then releasing that energy with reverse terminal voltage. The device uses a diode (also known as a flyback diode) to conduct and stop the energy transmission.

Current when switching on and off
Fig. 2: Current when switching on and off

When the primary coil switch is in the on-state then due to inductance, electrical current is built up. The secondary coil connected to the flyback diode in series opposes the current formation. Instead, the energy gets stored in the magnetic core.

Current when switched off

When the primary coil switch is in the off-state, the voltage polarity is reversed due to the magnetic law of induction, causing the diode to shift to forward bias. So now, the secondary coil starts conducting current.

Advantage of Flyback converter

  • Multiple voltages can be supplied while isolated from the primary winding.
  • Multiple voltages can be regulated with a single control
  • Can operate across a wide range of input voltage

Application of Flyback Transformer

  • CRT television to control horizontal control beam
  • Telecommunication system for DC-DC voltage conversion
  • ¬†Aeronautics for getting high voltage electric supply
  • Electric converters use this transformer in fluctuating frequencies and convert low voltage to high voltage
  • These transformers are also used along with industrial motors, generators and pumps

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