220V AC mains through the power transformer into a low voltage AC, and then through the bridge rectifier circuit D1 ~ D4 and filter capacitor C1 rectification and filtering, in the fixed three-terminal regulator LM7805 Vin and GND ends to form a not very stable DC voltage (the voltage is often due to fluctuations in the mains voltage or load changes, etc. reasons and changes). This DC voltage is regulated by LM7805 and filtered by C3 to produce a high precision and good stability of the DC output voltage at the output of the regulated power supply. This voltage regulator can be used as the power supply for TTL circuits or microcontroller circuits. Three-terminal voltage regulator is a standardized, series of general linear voltage regulator integrated circuits, with its small size, low cost, good performance, high reliability, simple and convenient to use, etc., to become a voltage regulator in the most widely used monolithic integrated regulator devices.
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