Regulator v2 — Switching 12 V → 5 V / 3.3 V

Overview

Regulator v2 is the switching-mode redesign of Regulator v1. It swaps the LM7805 + LDO stack for two Diodes Incorporated AP6320x synchronous buck converters — the AP63205 for the 5 V rail and the AP63203 for 3.3 V. Efficiency climbs from around 40% to over 90%, the board stays cool to the touch, and both rails can now source 2 A instead of 500 mA.

The mechanical envelope, terminal blocks, and DC jack all match v1 so the two boards are drop-in swappable in any bench setup.

Design intent

• Same shape, better power: identical mounting and connectors so it slots into any bench where v1 lived.
• AP6320x picked for beginner-friendliness: fixed-output-voltage variants, internal MOSFETs, no external compensation. All you provide is the input cap, output cap, and inductor.
• Low-EMI variant: the AP6320x parts spread the switching spectrum, which keeps radiated noise on the 3.3 V rail low enough for microcontroller supply duty.
• 4.7 µH Würth WE-LHMI inductors on both channels — shielded so magnetic coupling into nearby circuits is minimal.

Trade-offs vs v1

Switching converters add a little high-frequency ripple that v1's linear stack does not. For sensitive analog work (ADC references, op-amp front ends) you may still want v1. For anything digital or motor-driven, v2 is the clear win.

See the side-by-side comparison on the Regulator v1 page for the full trade-off table.

Status

This board is a working prototype. Gerbers have not been ordered yet — the current test bring-up is running on hand-populated bare KiCad-fab PCBs. Once the rails hold their voltage under a real load for 24 hours, I'll publish the fabrication package here.

Bringing it up

1. Populate the input side only. Apply 12 V. Verify the AP63205's VIN pin sees 12 V and its SW pin is quiet.
2. Populate the output stage of the 5 V channel. Verify 5.0 V ± 100 mV under no load, and under a 1 A dummy load.
3. Repeat for the 3.3 V channel.
4. Scope both rails at the terminal block with a 20 MHz bandwidth limit — ripple should be under 30 mV pk-pk.

Next revision (v3, planned)

• Add a USB-C input option alongside the barrel jack.
• Bring a shutdown pin out to a header for wake-on-external control.
• Drop the second-source AP63203 for a jellybean 3.3 V buck to make sourcing easier.