Flyback converter principle and practical reference design template

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L0504-Murata muRata common mode inductor 90Ω 150mA

This paper mainly explains the working principle, working mode and design of the flyback transformer topology of the switching power supply technology in detail, and emphasizes the design considerations of the flyback converter. The practicality of this paper is relatively strong. After determining the design conditions, according to the step-by-step calculation of the transformer design template, the novice can also complete the transformer design, which can also be used as a reference for experienced designers.

Flyback converters, also known as single-ended flyback or "Buck-Boost" converters, are named for their output gaining energy when the primary winding is turned off. In the flyback converter topology, when the switch is turned on, the transformer stores energy, and the load current is provided by the output filter capacitor; when the switch is turned off, the transformer transfers the stored energy to the load and the output filter capacitor to compensate the capacitor separately. The energy consumed when the current is loaded.

advantage:

a. The circuit is simple and can provide multiple DC outputs efficiently, so it is suitable for multiple sets of output requirements;
b. The output voltage can be increased or decreased. When the input voltage fluctuates within a large range, it can still have a stable output. Generally, the AC input can be between 85 and 265V, and the stable output can be achieved without switching.
c. High conversion efficiency and low loss;
D. The transformer turns ratio is small.
Disadvantages:
a. There is a large ripple in the output voltage, and the load adjustment accuracy is not high. Therefore, the output power is limited, and is usually applied to medium and small powers of 300 to 500 W or less;
b. The flyback transformer is essentially a coupled inductor that converts and stores energy. When operating in continuous current (CCM) mode, it has a large DC component. To prevent saturation of the core, it is necessary to add gas to the magnetic circuit. Gap, which causes the transformer to become larger;
c. The transformer has DC current component and will work in CCM / DCM mode as the load changes. Therefore, the transformer is difficult to design and the number of repeated adjustments will be more.

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