How to improve the reliability of the power system, with circuit diagram analysis

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Recently, the LLC topology has been favored by power supply design engineers for its high efficiency and high power density. However, this soft switching topology requires more MOSFETs than any previous hard switching topology. Especially in the case of power start, dynamic load, overload, short circuit, etc. The Infineon CoolMOS CFD2 series meets these needs with its high breakdown voltage, fast recovery body diodes, low Qg and Coss and greatly enhances the reliability of the power system.

For a long time, improving the power density, efficiency and reliability of power systems has always been a major issue for researchers. Increasing the switching frequency of the power supply is one of the methods, but the increase of the frequency will affect the switching loss of the power device, so that the lifting frequency is not very effective for the hard switching topology, and the hard switching topology has reached its design bottleneck. . At this time, soft switching topologies, such as LLC topology, are sought after by design engineers for their unique characteristics. But... This topology puts new demands on power devices.

The characteristics of the LLC circuit

The following features of the LLC topology make it widely used in a variety of switching power supplies:
1. The LLC converter enables zero voltage switching over a wide load range.
2. The output can be adjusted with a wide range of input voltage and load variations, while the switching frequency changes relatively little.
3. With frequency control, the duty cycle of the upper and lower tubes is 50%.
4. By reducing the voltage stress on the secondary synchronous rectifier MOSFET, a lower voltage MOSFET can be used to reduce cost.
5. Eliminate the need for an output inductor to further reduce system cost.
6. Higher efficiency can be achieved with a lower voltage synchronous rectification MOSFET.

See the PDF document for details.