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Project Specification — 12V Power Distribution Block
Project Overview
- Status: Draft
- A 50 mm × 100 mm PCB for distributing a 12V DC input to barrel-jack outputs and 3-pin fan connectors.
Intended Use
- Prototype / utility power distribution board for low-voltage 12V devices and fans.
- Not intended for mains voltage on the PCB.
What the Device Should Do
- Accept 12V DC through one 5.5×2.5 mm barrel input connector.
- Distribute the 12V bus to four 5.5×2.1 mm barrel output connectors.
- Distribute the same 12V/GND bus to four 3-pin fan connectors.
Main Features
- One 12V DC input connector.
- Four DC barrel output connectors.
- Four 3-pin fan connectors using +12V, GND, and an unconnected tach/sense/control pin unless later specified.
- Shared high-current copper bus for 12V and GND.
System Architecture
Diagram
Hardware Subsystems
- Power input: 5.5×2.5 mm DC barrel jack, rated for at least 10A if a suitable part is available.
- Power outputs: four 5.5×2.1 mm barrel jacks, each intended for 2A maximum.
- Fan outputs: four 3-pin fan headers tied to 12V and GND; third pin is currently not connected.
- PCB copper: 12V and GND should use wide traces and/or copper pours sized for 10A total input.
Interfaces and Connections
Table
| Interface | Quantity | Connection |
|---|---|---|
| 5.5×2.5 mm DC barrel input | 1 | Center positive assumed: +12V center, sleeve GND |
| 5.5×2.1 mm DC barrel output | 4 | Center positive assumed: +12V center, sleeve GND |
| 3-pin fan connector | 4 | Pin 1 GND, Pin 2 +12V, Pin 3 NC/Tach TBD |
Power and Runtime Expectations
- Input: 12V DC nominal.
- Total input current budget: 10A maximum.
- Each output connector current budget: 2A maximum.
- No battery or runtime constraint.
Power Tree and Power Budget
Table
| Rail | Source | Loads | Max Current |
|---|---|---|---|
| +12V | DC input jack | 4 barrel outputs + 4 fan connectors | 10A total |
| GND | DC input sleeve | Return for all outputs | 10A total return |
Manufacturing and Assembly Expectations
- Board size: 50 mm × 100 mm rectangle.
- Suggested stackup: 2-layer PCB with large top/bottom copper pours for 12V and GND.
- Connectors should be placed on long board edges: input on one long side, four barrel outputs on the opposite long side.
Firmware-Relevant Hardware Requirements
- None currently; no controller is included.
Physical Design Expectations
- 50 mm × 100 mm board.
- Input barrel jack on one long side.
- Four output barrel jacks on the opposite long side.
- Four fan connectors accessible from the board edge or near the output side.
Important Design Decisions
- Center-positive barrel polarity is assumed.
- The third fan connector pin is left unconnected until tach/PWM behavior is specified.
- Trace/pour sizing should be conservative for 10A total current.
Assumptions
- All connectors are PCB-mounted through-hole parts unless library availability requires otherwise.
- Barrel connectors are center-positive.
- No fuses, switches, LEDs, reverse-polarity protection, or per-output protection were requested yet.
Change Notes
- Initial requirements captured: 12V input, 10A total input, 2A per output, 50 mm × 100 mm PCB, one input jack, four output jacks, and four 3-pin fan connectors.
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