Summary: Under the condition that the electrical technical indicators meet the normal use requirements, in order to make the power supply work safely and reliably under harsh environment and sudden failure, it is necessary to design a variety of protection circuits, such as current limiting circuit and output voltage to prevent inrush current during power-on. Overshoot soft start circuit and overvoltage, undervoltage, overcurrent, short circuit protection circuit gates, etc. With the development of electronic technology, there are many types of control chips for switching power supplies. When forming DC/DC or AC/DC switching converters, UC3842 is the earliest current-type control chip, which is still the most widely used. PWM integrated controller. UC3842 has its own current detection comparator, which can realize output over-current and short-circuit protection. Its internal input under-voltage lockout circuit can also easily realize input under-voltage protection. Therefore, the switching power supply with UC3842 as the core is easy to use. The output overcurrent or short circuit protection is realized, and the input undervoltage protection r2 l is realized. However, in the UC3842-based switching power supply, how to implement input overvoltage protection has not been reported yet. In fact, such power supplies do not have input overvoltage protection, which makes the device a safety hazard. The input of overvoltage to the switching power supply is mainly caused by damage to the device due to the voltage and current stress exceeding the normal use range. At the same time, the electrical performance index may be damaged and cannot meet the requirements. Therefore, an overvoltage protection circuit must be used to improve the reliability and safety of the power supply. In this paper, a novel input overvoltage protection circuit is designed and applied to the switching power supply based on flyback converter with UC3842 as the core. The experimental results verify the feasibility of the design circuit. UC3842 internal circuit diagram and pin diagram Practical switching power supply circuit with input overvoltage protection See the upload document for details.
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