Application of LLC resonant conversion technology in switching power supply

　　With the rapid development of electronic technology and the increasing awareness of people's environmental protection, the requirements for power products in terms of size, efficiency, reliability, lifespan and comfort are getting higher and higher. Traditional switching power supply technology can no longer meet these requirements. . In 70W-500W AC-DC power supplies, switching power supplies using LLC resonant conversion technology are more efficient than traditional topology switching power supplies. Therefore, LLC resonant conversion technology is increasingly used in power supply products.

　　The figure below shows a typical half-bridge LLC resonant converter circuit:

　　Its equivalent voltage transmission relationship is:

　　fr1 is the resonant frequency of the resonant cavity

　　x is the normalized value of the switching frequency relative to the resonant frequency

　　k is the ratio of the transformer’s excitation inductance and resonant inductance.

　　Zr is the characteristic impedance of the resonant cavity

　　Re is the equivalent load AC impedance

　　Q is the quality factor

　　According to the voltage transmission relationship formula, the voltage transmission relationship curve under different variable conditions can be drawn:

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