Build Simple 12.6V CC/CV Lithium Battery Charger using Viper VP22A Low Power Primary Switcher IC

This project implements a switched-mode power supply (SMPS) operating in a flyback topology to deliver a regulated 12.6V Constant Current/Constant Voltage (CC/CV) output tailored for lithium battery charging. Mains AC voltage enters through a T500mA slow-blow fuse and is converted to high-voltage DC via a DB107G bridge rectifier and filtered using a 22uF 400V capacitor along with an AC capacitor. The Viper22A low-power primary switcher IC drives the custom EE25 SMPS transformer, rapidly switching the primary winding to transfer energy across the magnetic barrier. On the secondary side, an SR360 Schottky diode and an array of capacitors (including 1000uF and 16V variants) rectify and smooth the output into a steady DC voltage. Regulation and CC/CV profile control are managed using an LM358 operational amplifier, a TL431 programmable shunt regulator, and an EL817 optocoupler, which provides galvanic isolation by feeding error and current-sensing feedback from the output back to the primary-side Viper22A. Various resistors—such as the 1R 2W current-sense resistors and feedback components like the 10K, 1K, and 680R resistors—set the precise voltage thresholds and current limits. Visual feedback for the charging stages is provided by red and green LEDs.