Power management: based on PI LNK564DN flyback power supply circuit

The isolated flyback power supply shown in Figure 1 is designed around the LNK564DN (U1) from the LinkSwitch-LP product family. It can deliver 5 V/350 mA (1.75 W) over a universal input voltage range of 90-265 VAC.

Diodes D1 and D2 provide half-wave rectification of the AC input voltage. Storage capacitors (C1) and L1 attenuate conducted EMI. Inductor L1 is wrapped in heat shrink tubing and can be used as a fuse if any component is damaged.

The LNK564DN uses the reflected voltage of the secondary winding voltage on the bias winding to stabilize the output voltage and current , eliminating the need for an optocoupler. Regulation is achieved by skipping MOSFET switching cycles in the CV state (from no load to 1.75 W). When the load current exceeds the peak power point, the MOSFET switching cycles are no longer skipped, but the internal oscillation frequency is reduced proportionally with the voltage on the FEEDBACK (FB) pin, providing the CC portion of the output VI curve when this voltage reaches between 0.8-1.7 V. If the voltage on the FB pin is less than 0.8 V, U1 will enter the auto-restart state. During auto-restart, the controller switches the MOSFET for approximately 100 ms approximately every 800 ms. The LNK564DN will remain in the auto-restart state until the voltage on the FB pin rises above 0.8 V within the 100 ms switching cycle.