12V 1A SMPS Power Supply Circuit Design on PCB

This project designs a custom PCB-based Switched-Mode Power Supply (SMPS) capable of delivering a regulated 12V output from a high-voltage AC mains input ranging from 85V to 265V AC. The power conversion process begins at the input stage, where incoming AC power passes through a 1A 250VAC slow blow fuse (F1) for overcurrent protection, a 7mm 275V metal oxide varistor (RV1) to absorb voltage surges, and a common mode choke (L1) to suppress electromagnetic interference. The filtered AC voltage is then rectified into DC using a DB107 full bridge rectifier and smoothed out by high-voltage input capacitors (C1, C2). The core of the power conversion is managed by the TNY268PN power management IC, which works in conjunction with a switching transformer to efficiently step down the high DC voltage through high-frequency switching. On the secondary output side, diodes (such as D1, D2, D6) and output capacitors (C3 through C7) rectify and filter the transformer's high-frequency output into a steady DC voltage. To ensure tight regulation, a TL431 shunt regulator and an optocoupler form a feedback loop across the isolation barrier, communicating output voltage fluctuations back to the primary-side TNY268PN IC to dynamically adjust the switching duty cycle. The overall circuit layout and transformer characteristics are calculated and optimized using PI Expert software before being fabricated onto a custom PCB.