For such a low component count circuit, these new era power supply ICs take a bit of time to get your head around. Aside from the fact that they can accommodate over 375V DC directly (500V MOSFET), they have the MOSFET, current sensing and lots of control circuitry crammed into a tiny transistor-sized package.

This style of chip is appearing in many WiFi plugs where the PSU has to be tiny, but still drive a relay.

The three pin SOT23-3 version is suitable for up to about 100mA, while the bigger versions can accommodate higher current.

Let me know if I managed to explain the operation well.

Here are some datasheet links:-

Fremont Micro Devices FT8430.
https://datasheet4u.com/datasheet/FMD/FT8430-1571666

LANDP LP2178.
https://sharvielectronics.b-cdn.net/wp-content/uploads/2024/10/LP2178.pdf


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