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Universal Mini Router UPS Pro v1.0 — Feasibility and Architecture Notes
Current Architecture Decision
User selected a 3S Li-ion architecture for smooth router and ONU backup with automatic power-failure switchover. The design priority is that the router/ONU must not restart when adapter power fails.
Updated Battery Architecture
- Battery pack: 3S Li-ion / 18650 pack.
- Nominal pack voltage: 11.1V.
- Full charge voltage: 12.6V.
- Cutoff voltage target: 9.0V pack-level, assuming 3.0V/cell minimum.
- Pack connection: use welded pack pads or a rated 3S pack connector. Avoid spring holders for production/current reliability.
User Requirement Summary
- 12V DC adapter input via 5.5mm x 2.1mm barrel jack.
- 3S Li-ion battery pack.
- Safe battery charging with temperature monitoring and protection.
- Seamless automatic switchover to battery.
- Regulated outputs: 12V at 3A continuous / 4A peak, 9V at 2A, 5V USB at 3A.
- JLCPCB SMT assembly, compact PCB, production-ready reliability.
Power Budget Check
Worst-case simultaneous requested output power:
Table
| Rail | Voltage | Current | Power |
|---|---|---|---|
| 12V output | 12V | 3A continuous | 36W |
| 9V output | 9V | 2A | 18W |
| 5V USB output | 5V | 3A | 15W |
| Total load | 69W |
Battery-side current at 3S cutoff voltage, assuming 90% conversion efficiency:
I_BAT = P_OUT / (V_BAT_MIN × efficiency) = 69W / (9.0V × 0.90) = 8.52A12V-only load at 3A requires:
I_BAT_12V_ONLY = 36W / (9.0V × 0.90) = 4.44A12V peak load at 4A requires:
I_BAT_12V_PEAK = 48W / (9.0V × 0.90) = 5.93AKey 3S Design Implication
A 3S pack makes the power current practical compared with 1S, but it introduces a charger constraint: a simple buck charger cannot fully charge a 3S pack from a 12V adapter because the pack requires 12.6V at full charge plus charger headroom. Therefore the design must use one of:
- A buck-boost 3S charger / power-path controller that can charge a 12.6V pack from a 12V input.
- A higher-voltage adapter input such as 15V to 20V, allowing a simpler buck charger.
- A separate boost-precharger stage feeding a 3S charger, which is less preferred for compact production.
Because the user wants 12V adapter input, the preferred production architecture is a buck-boost charger / power-path controller.
No-Reboot Switchover Strategy
To avoid router/ONU reboot during adapter failure:
- Use an always-regulated 12V system output rail from a 4-switch buck-boost regulator. It regulates 12V whether the source is 12V adapter or 3S battery.
- Use ideal-diode / power-path control so the adapter powers the system when present and the battery takes over when the adapter fails.
- Add low-ESR bulk hold-up capacitance on the 12V output rail to cover controller handoff, load transient, and cable inductance.
- Keep the 12V rail continuously enabled while the main power switch is on.
- Detect adapter present and battery mode with comparator/MCU GPIO, but do not rely on firmware timing for the actual power-path switchover.
Proposed Functional Blocks
- Input protection: barrel jack, fuse/eFuse, reverse-polarity protection, TVS, input-voltage sensing.
- 3S charger and power path: buck-boost charger, NTC thermistor, charge status, pack connector, balancing/protection.
- Battery protection/BMS: overcharge, over-discharge, over-current, short-circuit protection, cell sense lines.
- 12V no-reboot output: 4-switch buck-boost regulator, ideal-diode source selection or power-path ORing, output current protection, hold-up capacitors.
- 9V output: buck converter from 12V system rail.
- 5V USB output: buck converter from 12V system rail with USB-A connector protection.
- Monitoring/UI: MCU, fuel gauge, LEDs, push button, optional OLED/I2C header, test points.
- Mechanical/manufacturing: mounting holes, edge connectors, JLCPCB SMT assembly, thermal copper.
Design Direction
Proceed with 3S architecture using an always-regulated 12V buck-boost output and a buck-boost 3S charger/power-path design so router/ONU loads do not see a power gap during adapter failure.
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