Circuit principle of PFC+ unregulated isolated converter to obtain high efficiency switching power supply

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Overview:
The rising global energy prices have caused all industries to seriously consider the issue of energy conservation. Among various energy-saving methods, improving the efficiency of the switching power supply is an important means. The United States has introduced the 85PLUS and 88PLUS plans since the introduction of the 80PLUS program, and implemented it in the short term. Therefore, it is the goal of the power industry to continuously improve the efficiency of the switching power supply.

In order to improve the efficiency of the switching power supply, it is first necessary to clearly understand the factors affecting the switching power supply. In general, the flyback and its derivative circuits are the least efficient, and the multipole transform circuit topology is less efficient than a single-stage transform. Therefore, the above circuit topology should be avoided as much as possible in the application.

For forward power conversion, the greater the duty cycle, the higher the efficiency. Therefore, the actual duty cycle should be as large as possible. If the duty ratio is close to 1, it is ideal.

A switching power supply with a large input voltage variation range is less efficient than a range of input voltage variations. Avoiding large variations in input voltage or avoiding unnecessary input voltage change margins is one of the easiest ways to increase the efficiency of switching power supplies.

As switching frequencies get higher and higher, switching losses are a factor that cannot be ignored. A simple RCD snubber circuit approach is an important factor affecting efficiency. Therefore, the use of soft switching, zero voltage switching can effectively eliminate switching losses.

With a MOSFET of 400 to 700V, the conduction loss may account for two-thirds of the total loss. Therefore, trying to reduce the on-resistance of the MOSFET can effectively reduce the loss of the MOSFET.

Based on the above factors, we propose a method for obtaining a high-efficiency switching power supply using a combination of PFC+ unregulated isolated converters. PFC control is realized by MC33368, and DC/DC conversion is performed by IRS2453 self-vibration full-bridge converter.
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