What Is a Flyback Converter?

A flyback converter is a buck-boost converter in which the electrical current is isolated, preventing energy from carrying over between the inputs and outputs. It is used in applications with both alternating current (AC) and direct current (DC). A transformer is formed inside the circuit by splitting the inductor, and flyback converters are used in high power systems, such as computers and televisions, to allow them to consume as little power as possible. They are preferred mainly because they use fewer components than other electrical devices, and are relatively inexpensive to include.

The flyback converter operates by switching quickly between on and off states. A metal oxide semiconductor field effect transistor (MOSFET) and diode are used to control the switching. When the converter is in an on-state, a transformer stores energy and then releases it when the unit is switched off. The tight coupling of the primary with the secondary windings minimizes the leakage inductance, or drop in current due to magnetic flux between misaligned windings. In a flyback converter, the energy generated by this is released as heat.

When the flyback converter switch is in the on-state, the transformer’s primary input and the input voltage source are linked. If it is off, the switch allows energy to move from the transformer to the converter’s output. With energy stored in the transformer, several outputs can be included. The converters also have a rail that loads in order for the transformer to be energized via pulse width modulation.

By allowing for low power consumption, the electrical power conversion from a flyback converter is suited for devices operating from 50 to 100 watts. Each output added consists of its own winding, diode, and capacitor, and multiple outputs can add enough voltage to increase the leakage inductance. The ringing voltage caused by this can be reduced by a snubber circuit. This ensures adequate protection based on the type of transistor used.

Eliminating the diode from the system classifies the unit as a flyback transformer, which is used to run a plasma lamp or voltage multiplier. In general, the converter and the control circuit each have to be isolated on a flyback converter. Current mode control is essential to stabilize the power output. Signals for voltage mode control are created using an optocoupler on the circuit or by using an additional coil winding. Regulation of voltage and current modes is important for items such as phone chargers, which require high accuracy that is attained using thorough waveform analysis and computer-driven design principles.