Created:2026/05/07
Updated:2026/05/07
Author:
Takeshi Takatsudo

Project Status and Plan

Current progress and future plans for the USB-PD powered modular synthesizer power supply.

🎯 Project Goal

Low-noise power module supplying ±12V/+5V for modular synths from USB-C PD 15V input

Protection circuit safe for modular synth beginners
All parts available from JLCPCB (stable supply, low cost)
Low-noise design with <1mVp-p ripple
Easy to use with USB-C PD

✅ Completed Items

1. Circuit Design (100% Complete)

4-Stage Architecture Completed:

USB-C 15V ──┬─→ +13.5V (DC-DC) ──→ +12V (LDO) ──→ +12V OUT
            │
            ├─→ +7.5V  (DC-DC) ──→ +5V  (LDO) ──→ +5V OUT
            │
            └─→ -15V (Inverter) ──→ -13.5V (DC-DC) ──→ -12V (LDO) ──→ -12V OUT

✅ Stage 1: USB-PD Power Supply (STUSB4500)
✅ Stage 2: DC-DC Converters (LM2596S × 3 + LM2586 inverted SEPIC)
✅ Stage 3: Linear Regulators (LM7812/7805/7912)
✅ Stage 4: Protection Circuit (PTC + Fuse + TVS)

2. Parts Selection (100% Complete) ✅

All parts confirmed: All JLCPCB part numbers finalized

✅ USB-PD Controller: STUSB4500 (C2678061)
✅ DC-DC Converter: LM2596S-ADJ × 3 (C347423)
✅ Voltage Inverter: LM2586SX-ADJ/NOPB (C181324)
✅ Linear Regulators: L7812CV-DG (C2914) / L7805ABD2T-TR (C86206) / CJ7912 (C94173)
✅ Inductors: 100µH 4.5A × 3 (C19268674)
✅ TVS Diodes: SMAJ15A, SD05
✅ Fuses: 1.5A × 2 confirmed (C95352)

~~Unconfirmed Parts~~ → All Confirmed! ✅

✅ PTC Resettable Fuses × 3
- PTC1: 1.1A 16V (1812) → C883148 (BSMD1812-110-16V)
- PTC2: 0.75A 16V (1206) → C883128 (BSMD1206-075-16V)
- PTC3: 0.9A→1.1A 16V (1812) → C883148 (BSMD1812-110-16V) ※
✅ 2A SMD Fuse × 1 (for +12V) → C5183824 (6125FA2A)

※ 0.9A part out of stock. 1.1A provides sufficient protection margin for -12V actual load of 800mA.

3. Documentation (100% Complete)

✅ Complete circuit diagrams (all 10 stages)
✅ Detailed BOM (with JLCPCB part numbers)
✅ Design philosophy and architecture explanation
✅ Protection circuit operation description

4. Cost Estimation (100% Complete) ✅

Total with all parts confirmed: $4.68/board

Stage 1: $0.43
Stage 2: $2.09
Stage 3: $0.37
Stage 4: $1.79 (all parts confirmed price)

5. PCB Layout (100% Complete) ✅

PCBA v2 layout complete — DRC clean as of 2026-04-18:

✅ R14 (470 Ω) placed — VBUS_IN to VBUS_VS_DISCH (pin 18) pull
✅ R15, R16 (4.7 k each) placed — I2C pull-ups for NVM programming interface
✅ J2 placed — pogo pad footprint for NVM programming access
✅ All components placed and routed
✅ DRC run with zero errors

🔄 Current Status

Where Are We Now?

PCBA v2 schematic and PCB layout complete — ready to generate manufacturing files

Full project history to date:

✅ Circuit design complete — Working 4-stage design finalized
✅ All parts selection complete — JLCPCB part numbers confirmed (100%), optimized to high-stock parts
✅ BOM fully confirmed — Cost $4.68/board
✅ PCBA v1 ordered and tested — Board powered up but STUSB4500 failed to negotiate USB-PD. Root cause: pin 18 (VBUS_VS_DISCH) unconnected, pin 22 (VSYS) shorted to VREG_2V7. Bodge wires applied for analysis.
✅ v2 schematic fixes applied — R14 (470 Ω, pin 18 pull), R15/R16 (4.7 k I2C pull-ups), J2 (pogo pads for NVM programming) added. VSYS connected to GND.
✅ v2 PCB layout complete — All components placed and routed. DRC clean as of 2026-04-18.
⏳ Generate manufacturing files — Gerbers, drill files, BOM, CPL for JLCPCB reorder ← This is next!

Hardware Acquired

NUCLEO-F072RB (STM32 Nucleo board, used as USB-to-I2C bridge for STUSB4500 NVM programming) — purchased
4P 2.54 mm pogo pin clip (AliExpress item 1005006108783889, mates with J2 pogo pads) — purchased
PCBA v1 physical boards — N boards retained for bodge reference (see JLCPCB order history)

What's Next?

Generate Gerber/BOM/CPL files and place PCBA v2 order at JLCPCB

✅ Schematic and PCB layout done — v2 schematic and layout with all debug fixes applied
✅ DRC clean — Zero errors as of 2026-04-18
📐 Next Action: Generate manufacturing files from KiCad

Gerber files → Drill files → BOM (JLCPCB format) → CPL (component placement)

📋 Next Steps (Priority Order)

🔴 Priority: High - Do Immediately

Step 1: Search for Unconfirmed Parts ✅ Complete!

Parts found:

✅ PTC Resettable Fuses × 3 types

PTC1 (1.1A 16V, 1812): C883148 - Stock: 11,029
PTC2 (0.75A 16V, 1206): C883128 - Stock: 51,532
PTC3 (1.1A 16V, 1812): C883148 - Stock: 11,029 ※0.9A part unavailable

✅ SMD Fuse (2A 250V)

C5183824 (6125FA2A, 2410 package) - Stock: 744

Step 2: Finalize BOM ✅ Complete!

✅ Part numbers added to /notes/parts.md
✅ Final cost calculated: $4.68/board
✅ Reflected in /doc/do../components/bom.md
✅ All parts optimized to high-stock items (CH224D, L7812/7805, CJ7912)

🟡 Priority: Medium - Do Next

Step 3: Prepare PCB Design ✅ Complete!

KiCad Project Setup:

Create new KiCad project
Enter circuit in schematic editor
Add JLCPCB footprint library
Assign footprints to all parts

Required footprints:

/footprints/CH224D.png - Already available
/footprints/USB-TYPE-C-009.png - Already available
Other standard footprints use KiCad standard library

Step 4: PCB Board Design ✅ Complete!

Layout Policy:

4-Layer Board Structure:

Layer 1 (Top): Signals + component placement
Layer 2 (Inner): GND plane
Layer 3 (Inner): Power plane (+15V, +12V, etc.)
Layer 4 (Bottom): Signals

Power Layout:

Place USB-PD → DC-DC → LDO in sequence
Physically separate high-noise (DC-DC) and low-noise (LDO) sections
Make high-current paths thick and short

Thermal Design:

LM2596S (TO-263) → Place thermal vias
LM78xx/79xx (TO-220) → Reserve heatsink area
Consider electrolytic capacitor heat dissipation

JLCPCB Design Rules:

Minimum trace width: 6mil (0.15mm)
Minimum clearance: 6mil
Via diameter: 0.3mm (hole 0.2mm)

🟢 Priority: Low - Pre-Prototype Preparation

Step 5: Generate Manufacturing Files (Time: 1 hour) ← We are here!

Generate Gerber files
Generate Drill files
Generate BOM file (JLCPCB format)
Generate CPL file (component placement data)

Step 6: Get JLCPCB Quote (Time: 30 minutes)

Quote contents:

PCB manufacturing: 5 or 10 boards
SMT assembly: both sides or single side
Parts procurement cost
Shipping

Estimated Cost (for 10 boards):

PCB manufacturing: ~$30
SMT assembly: ~$50-100
Parts cost: ~$50 (for 10 boards)
Shipping: ~$20
Total: $150-200 (10 boards = $15-20 per board)

Step 7: Order Prototype (Time: 15 min order + 2 weeks manufacturing)

Recommended Initial Order:

Quantity: 5-10 boards
SMT assembly: All parts installed
Delivery: DHL (2-3 weeks)

PCBA v1 Failure Findings

The first prototype PCBA (v1) failed during testing. The STUSB4500 USB-PD controller did not negotiate power delivery. Root cause analysis identified three issues:

Issues Found

Pin 18 (VBUS_VS_DISCH) not connected - This pin was left as NC but must be connected to VBUS_IN via a 470ohm series resistor for VBUS voltage sensing. This is a critical connection required by the datasheet.
Pin 22 (VSYS) floating - After cutting the incorrect VSYS-to-VREG_2V7 trace, VSYS was left floating. The datasheet requires VSYS to be connected to GND when not used.
Pin 22 (VSYS) shorted to Pin 23 (VREG_2V7) - A routing error in the original schematic connected these pins together, overloading the internal 2.7V regulator. Fixed by cutting the trace on the PCBA.

Required Schematic Fixes Before Next Order

Add R14 (470ohm) from VBUS_IN to VBUS_VS_DISCH (pin 18)
Connect VSYS (pin 22) to GND
Verify VREG_2V7 (pin 23) decoupling is correct (C30 only)
Run DRC and review all STUSB4500 connections

See the full PCBA v1 Debug Report for detailed analysis, bodge wire instructions, and reference design comparison.

🤔 Design Concerns and Considerations

Issues Resolved in Current Design

✅ Noise countermeasure: DC-DC + LDO 2-stage design expected to achieve <1mVp-p
✅ Beginner-friendly: PTC auto-reset for automatic recovery from overload
✅ Cost: Parts cost under $5 using many Basic Parts
✅ Procurement stability: All parts have abundant JLCPCB stock

Items Not Yet Verified (Confirm with Prototype)

⚠️ Thermal design: Is LM2596S heat dissipation sufficient?

Maximum loss: Each 1.5V × 1A = 1.5W
TO-263 package should handle it but needs actual measurement

⚠️ Ripple noise: Can actual measurement achieve <1mVp-p?

Design should be fine but needs measurement

⚠️ Efficiency: Can actual measurement achieve 75-80%?

LM2596S: 85-90%
LDO loss: 10-15%
Calculated overall efficiency: 75-80%

⚠️ EMI/EMC: DC-DC switching noise impact?

Countermeasures with input/output filters but needs measurement

📝 Design Philosophy Review

Why This Design?

DC-DC + LDO 2-Stage Method

Reason: Balance efficiency and noise
DC-DC only: Efficient but high ripple
LDO only: Low noise but poor efficiency (high heat)
2-stage: Best of both worlds ✨

USB-C PD 15V Input

Reason: Can use generic chargers
No AC adapter needed → Easy to carry
Any PD-compatible charger works
15V voltage optimal for generating ±12V

All Parts from JLCPCB

Reason: Stable supply, low cost, automated assembly
Many Basic Parts → No extra fees
Abundant stock → Long-term procurement possible
SMT automated assembly → No hand soldering needed

PTC Auto-Reset Protection

Reason: Safe for beginners
Module overload → Notice when LED goes out
Auto-reset after 30 seconds → No repair needed
Fuse for short circuits → Safety ensured

🎯 Project Goals

Final Goal

"Manufacture beginner-friendly modular synth power supply with JLCPCB for under $20/board"

Achievement Criteria

Ripple noise <1mVp-p (measured)
Efficiency 75-80% (measured)
Output voltage accuracy ±1% (measured)
Overload protection operation confirmed (LED off → auto-reset)
Short circuit protection operation confirmed (fuse blown)
Manufacturing cost under $20/board (when ordering 10 boards)

Secondary Goals

📖 Comprehensive English documentation → Contribute to international Maker community
🔧 Open-source KiCad project
📝 Write build article (Blog/Medium)
🎓 Share JLCPCB SMT utilization know-how

💡 What You Can Do Now

After reading this document, you can immediately start:

5 minutes: Search for parts ✅ Complete!
30 minutes: Update BOM ✅ Complete!
1 hour: Install KiCad and create new project ✅ Complete!
1 day: Enter complete circuit in schematic editor ✅ Complete!
1 hour: Generate Gerber/BOM/CPL files in KiCad and place PCBA v2 order ← Start here!

PCBA v2 schematic + layout done and DRC clean! Generate manufacturing files and reorder! 🚀

🎯 Project Goal​

✅ Completed Items​

1. Circuit Design (100% Complete)​

2. Parts Selection (100% Complete) ✅​

3. Documentation (100% Complete)​

4. Cost Estimation (100% Complete) ✅​

5. PCB Layout (100% Complete) ✅​

🔄 Current Status​

Where Are We Now?​

Hardware Acquired​

What's Next?​

📋 Next Steps (Priority Order)​

🔴 Priority: High - Do Immediately​

Step 1: Search for Unconfirmed Parts ✅ Complete!​

Step 2: Finalize BOM ✅ Complete!​

🟡 Priority: Medium - Do Next​

Step 3: Prepare PCB Design ✅ Complete!​

Step 4: PCB Board Design ✅ Complete!​

🟢 Priority: Low - Pre-Prototype Preparation​

Step 5: Generate Manufacturing Files (Time: 1 hour) ← We are here!​

Step 6: Get JLCPCB Quote (Time: 30 minutes)​

Step 7: Order Prototype (Time: 15 min order + 2 weeks manufacturing)​

PCBA v1 Failure Findings​

Issues Found​

Required Schematic Fixes Before Next Order​

🤔 Design Concerns and Considerations​

Issues Resolved in Current Design​

Items Not Yet Verified (Confirm with Prototype)​

📝 Design Philosophy Review​

Why This Design?​

🎯 Project Goals​

Final Goal​

Achievement Criteria​

Secondary Goals​

💡 What You Can Do Now​