PCB Design for UV Water Filter
Worked for 5 mins 5 sec
I’m blocked because the account has no available ACUs, so I can’t continue executing schematic/layout changes right now.
What I completed this session:
- Read the attached document and extracted the required architecture: USB-C → CH224K PD trigger at 9 V → AL8860 buck constant-current driver → 2-pin off-board UV-C LED output
- Confirmed: UV-C LED must not be placed on the PCB
- Researched and identified library parts for:
- CH224K USB-PD trigger
- AL8860 buck LED driver
- HT7333-A 3.3 V LDO
- ATtiny412 SOIC-8
- SS14 Schottky diode
- USB-C 16-pin receptacle
- UPDI header, button, status LED, interlock/output connectors
- Extracted key datasheet facts:
- AL8860 LED current: I = 0.1 / Rsense
- 0.30 Ω sets about 333 mA
- CH224K 9 V request can use CFG logic or RSET configuration
- HT7333-A supports 3.3 V output from 9–12 V input
- ATtiny412 UPDI is on PA0 / RESET / UPDI
What remains:
- Replace the current old schematic with the new CH224K + AL8860 + ATtiny412 design.
- Add the exact BOM values from the document.
- Add the 2-pin output connector instead of onboard UV-C LED.
- Update project docs and firmware notes.
- Create the under-40 × 40 mm 2-layer layout following Section 5.
- Run ERC/DRC and fix issues.
List exact BOM
Rebuild schematic first
Check old parts
Review layout constraints
Refine this doc
Ask about this doc
Project Specification
Project
USB-C UV-C Water Sterilizer LED Driver
Goal
Design a low-cost PCB powered from USB-C 5 V to drive a UV-C LED for a drinking-water sterilization prototype.
Confirmed Requirements
- UV source: UV-C LED
- Input power: USB-C 5 V
- Target use: drinking-water sterilization
- Low-cost implementation
Current Architecture
- J1: USB-C 5 V power-only input
- R1/R2: 5.1 kΩ CC pull-down resistors for USB-C sink operation
- F1: 500 mA hold resettable fuse on USB input
- U1: BCR421 linear constant-current LED driver
- D1: 275 nm UV-C LED
- J2: external lid/flow safety interlock; open interlock pulls EN low through R5
- D2/R4: visible UV-on status indicator
- C1/C2: input and local bypass capacitance
Important Assumptions
- This is a prototype driver board, not a validated water sterilizer product.
- One UV-C LED is used because many 275 nm LEDs have high forward voltage; two in series from USB 5 V usually needs a boost driver.
- Final UV dose depends on LED radiant power, chamber geometry, water transmittance, exposure time, and flow rate.
- A closed opaque chamber and interlock are mandatory before energizing UV-C.
Safety Notes
UV-C radiation can injure eyes and skin. Do not power the UV-C LED outside a fully enclosed chamber. Use the interlock connector with a normally-open/closed safety switch appropriate to the enclosure so the LED cannot turn on when the chamber is open. Drinking-water sterilization requires microbiological validation and is not guaranteed by this PCB alone.
Open Engineering Items
- Confirm desired water flow rate and chamber volume.
- Confirm target UV dose and LED radiant output.
- Verify BCR421 current-set resistor value from the datasheet for the selected LED current.
- Check thermal design for D1 and U1; UV-C LED lifetime strongly depends on junction temperature.
- Add PCB layout with thermal copper under D1 and short high-current loop routing.
Project
Goal
Confirmed Requirements
Current Architecture
Important Assumptions
Safety Notes
Open Engineering Items
