In the development of new switching power adapters, engineers usually provide appropriate output overload protection for ACDC adapters in order to ensure that adapters can adapt to the operation requirements of different environments and provide continuous and stable current and voltage conversion for users during the use of adapters to ensure the safe operation of adapters. . This article will introduce two widely used output overload protection technologies to help engineers better complete the design of new adapter products.
Constant power limit protection method
Constant Input Power Limit Protection (CIRP) is one of the most popular output protection techniques for switching power adapters in the world. The principle of this method is to protect the primary circuit by limiting the maximum transmission power. But in the flyback converter, this technology can hardly protect the secondary output components. For example, in a discontinuous flyback converter, the peak current of the original side has been limited, that is, the limited transmission power is given. When the load resistance decreases and the load exceeds its limiting value, the output voltage begins to decrease.

It is precisely because the voltage-current product of the input and the corresponding output is specified that when the output voltage begins to drop, the output current will rise. In short circuit, the secondary side current will become very large and consume all power in the switching mode power supply. This form of power limitation is generally only used as a supplementary form of some limitations, such as the sub-boundary current in a circuit with supplementary limitations.
Flyback super power limited protection
The counterattack overpower protection method is widely used in adapter research and manufacture in China. This protection technology is an extension of the high-speed mode, in which there is a circuit to monitor the primary side current and secondary side voltage and reduce power when the output voltage is reduced. In this way, when the load resistance drops, the output current decreases and the secondary edge components are prevented from being damaged by excessive stress. The disadvantage of this method is that lock-in occurs when used for nonlinear loads.