USB-PD AC Adapter

USB-PD AC adapter requirements for zudo-pd. The adapter plugs into Board A, the USB-PD sink core, which negotiates 15 V and hands the switched rail to Board B.

Required Specifications

Why 15V / 3A?

Board A uses the STUSB4500 USB-PD sink controller, NVM-configured to request the 15 V PDO (Power Data Object).

Power Budget Calculation:

At the design-target conversion efficiency (~75-80%, itself unmeasured), the input draw is roughly 33-35 W — about 2.2-2.4 A at 15 V. A 45 W adapter (15 V/3 A) therefore covers the full budget with headroom for inrush and the DC-DC stage's startup behavior.

Important Considerations

1. Must Support 15V PDO

Critical: The adapter must explicitly support 15V in its PDO profile.

Some cheaper adapters only support:

• 5V / 9V / 20V (skipping 15V)

Always verify the product specifications list 15V as a supported voltage.

2. Single Port Usage (For Single zudo-PD)

When using multi-port adapters with a single zudo-PD unit, power is typically split between ports. For reliable operation:

• Use a single USB-C port for full power delivery

• If using multi-port, ensure the port supports 45W+ when used alone

Note: For multi-case setups with multiple zudo-PD units, using a single high-wattage multi-port charger is what removes ground loops. See Multi-Case Setup below.

3. GaN Technology Recommended

GaN (Gallium Nitride) adapters offer:

• Smaller size

• Higher efficiency

• Lower heat generation

• Better reliability

4. Avoid No-Brand Adapters

Cheap no-brand adapters may:

• Have unstable voltage output

• Skip 15V PDO entirely

• Lack proper safety certifications (PSE in Japan)

Candidate Products (Amazon Japan)

These are shortlisted on published specs only. None has been confirmed against a working board, for the reason in the warning at the top of this page.

Product Links

1. Anker Nano II 65W — single-port, ample margin

• Compact design with GaN II technology

• Output: 5V/3A, 9V/3A, 15V/3A, 20V/3.25A

2. Anker Nano II 45W — minimum spec, most compact

• Smallest form factor

• PPS support

• Output: 5V/3A, 9V/3A, 15V/3A, 20V/2.25A

3. UGREEN Nexode 65W — multiple ports

• 3 ports for versatility

• GaN II technology

• PD3.0 and PPS support

4. BESTEK G651CA1 65W — budget option

• Explicitly lists 15V/3A support

• Compact design (~102g)

5. Belkin WCH013dq 65W — premium option

• 5V/9V/12V/15V/20V support

• Dual USB-C ports

6. CIO NovaPort SLIM 45W — ultra-thin design

• Only 13mm thick

• Dual USB-C ports

Verification Before Purchase

Before purchasing, check the product page for:

1. PDO List - Should include 15V (e.g., "5V/9V/15V/20V")

2. Power at 15V - Should be at least 3A (45W)

3. Safety Certification - PSE mark for Japan

4. Reviews - Check for stability issues

Charger Compatibility: What Is and Is Not Known

The observations

Bench attempts across the PCBA orders produced these results:

Why multi-port chargers are still the harder case

The hypothesis below is retained because it shapes what to test first once Board A works, not because this project's bench results support it.

Simple PD sink controllers have narrower negotiation behavior than the software PD stacks in laptops and tablets. Multi-port GaN chargers with intelligent power management assume an active, responsive sink:

• Dynamic power management — multi-port chargers redistribute power as devices connect and disconnect, re-advertising PDOs in real time

• Non-standard timing — some high-wattage chargers hold VBUS at 0 V until specific conditions are met, or run longer negotiation sequences

• Missing 5 V PDO — a charger whose Source_Capabilities starts above 5 V violates the USB PD spec's PDO1 requirement and can strand a simple sink at the pre-PD 5 V default

The STUSB4500 was chosen partly because it is USB-IF certified and has built-in retry and error recovery, which is the class of behavior these chargers demand.

Symptoms of a failed negotiation

When the 15 V contract is never established (whatever the cause):

1. Only the -12V LED briefly flickers

2. All LEDs turn off

3. No output voltage on any rail

Explanation: With only 5 V present, the DC-DC converters cannot produce their target voltages. The U4 inverting buck-boost (LM2596S-ADJ) briefly attempts to invert whatever voltage exists, which is what flickers the -12V LED.

This is the signature the v1-v4 boards produced. Note it is a sink-side observation: per the diagnosis page, a contract that forms and then collapses within a few hundred milliseconds is indistinguishable from "no negotiation" on a DMM — only a scope on VBUS_IN and CC separates them.

Recommended approach

1. Start with a dedicated single-port charger — the simplest negotiation, and the smallest set of variables while Board A is under bring-up

2. Test before relying on any charger, particularly a high-wattage multi-port GaN unit

3. Report what you find — this project has no compatibility data to hand you, so a confirmed result is genuinely new information

Troubleshooting

Adapter Not Working

If the power supply doesn't work with your adapter:

1. Check PDO support - Adapter may not support 15V

2. Check cable - Use a USB-C cable rated for 3A or higher

3. Check port - Some multi-port adapters reduce power on certain ports

4. Check the board - Given the bring-up history, work through the bench discrimination procedure before concluding the adapter is at fault

LED Not Lighting

The three rail indicators all live on Board B: LED2 (green) on +12 V, LED3 (blue) on +5 V, LED4 (red) on −12 V. All three dark means Board B never received 15 V, which points at Board A's negotiation rather than at any single rail:

1. Verify adapter is connected and powered

2. Try a different USB-C cable

3. Verify adapter supports 15V PDO

4. Verify the J4 ↔ J5 interface cable is seated — Board B has no other power source

A single dark LED with the other two lit is the opposite situation: the 15 V contract is fine and that one rail has tripped its PTC or lost its regulator.

Multi-Case Setup (Multiple zudo-PD Units)

When you need more power for a larger modular synth system, you can power multiple zudo-PD units from a single multi-port USB-PD charger. This approach has significant benefits over using separate AC adapters.

Why Use a Single Multi-Port Charger?

Ground Loop Elimination:

When using separate AC adapters for each case, connecting modules via patch cables creates ground loops:

Separate Adapters (BAD):
┌─────────────────┐          ┌─────────────────┐
│   Adapter A     │          │   Adapter B     │
│   GND_A         │          │   GND_B         │
└────────┬────────┘          └────────┬────────┘
         │                            │
    ┌────┴────┐                  ┌────┴────┐
    │ Case A  │◄───patch cable───│ Case B  │
    └─────────┘   (has ground)   └─────────┘
         │                            │
         └─────── ground loop ────────┘
              ↑
         Potential 50/60Hz hum

Single multi-port charger solves this:

Single Multi-Port Adapter (GOOD):
┌─────────────────────────────┐
│  Multi-Port GaN Charger     │
│  (shared internal ground)   │
└──────┬─────────────┬────────┘
       │             │
   ┌───┴───┐     ┌───┴───┐
   │zudo-PD│     │zudo-PD│
   │ Case A│◄───►│ Case B│  ← Patch cables OK!
   └───────┘     └───────┘

No ground loop - both share same ground reference!

Power Requirements

Each zudo-PD unit draws approximately 35 W at 15 V (≈2.4 A) at its full rail budget — but it negotiates a 15 V/3 A contract, so budget the charger against the 45 W contract, not the 35 W draw.

Important Considerations

1. 15V must be maintained on all ports - Some chargers drop to 9V when power is split

2. Check simultaneous output specs - Not just total wattage, but per-port when multiple ports are used

3. USB Hubs don't work - Regular USB hubs only provide 5V, not USB-PD

⚠️ Nothing below is verified

No multi-port charger has been shown to work with zudo-PD — and neither has any single-port one. See Charger Compatibility above. The chargers listed here meet the wattage and PDO requirements on paper; that is all that can be said about them today.

Before committing to a multi-port charger for a multi-case setup:

1. Confirm the published per-port specs hold 15 V when all ports are loaded

2. Consider multiple single-port chargers instead, with ground-loop mitigation

3. Test before relying on it for live performance

Multi-Port Chargers (Unverified — Use at Your Own Risk)

These chargers have sufficient power specifications on paper but have not been verified with zudo-PD:

For 2 zudo-PD Units

For 3 zudo-PD Units

Note: If you find a charger that negotiates 15 V with zudo-PD, please report it — it would be the project's first working data point.

Verification Checklist

Before purchasing a multi-port charger for multi-case setup:

• Total wattage ≥ (number of units × 45W)

• Supports 15V PDO on multiple ports simultaneously

• Check reviews for multi-device usage scenarios

• Verify power distribution when all ports are used (check manual or QR code specs)

Alternative: Separate Single-Port Adapters

Separate single-port adapters trade the ground-loop benefit for the simplest possible negotiation per unit:

Pros:

• ✅ Simplest, most predictable PD negotiation

• ✅ Each unit has dedicated power, no per-port sharing to reason about

Cons:

• ⚠️ Potential ground loops when connecting patch cables between cases

• ⚠️ More wall outlets needed

Ground Loop Mitigation (if using separate adapters):

1. Use balanced audio connections where possible

2. Ground lift on one case (if your synth supports it)

3. Use the same power strip for all adapters (shared AC ground)

4. Avoid connecting patch cables between separately-powered cases during performance