An accurate CV-CC non-isolated buck battery charger using primary side PWM controller

Primary side flyback PWM controllers are available with large number of protection features such as over current protection, over/ under input voltage protection, over output voltage protection etc., and designs using such controllers can be cost effective. They are designed for flyback dc-dc converters for low power CV-CC applications like LED lighting and mobile/PDA battery chargers. Using this type of controllers for a Buck type CV-CC battery charger, which can be designed for higher power levels is a low cost option. It offers accurate CV-CC control function with a stable change over between constant current and constant voltage regimes. It is shown that the resulting design can fully utilize the protection features, which increases safety and reliability. This paper presents the design of a 14V, 7W CV-CC battery charger using such an integrated controller and explains the modifications required for the flyback controller to work as a buck CV-CC charger.