BAJA POWER
DISTRIBUTION

I designed a custom Power Distribution Board (PDB) for Olin Baja's off-road race vehicle, replacing ad hoc battery wiring with a centralized, protected power architecture. The board accepts a 9–12 V battery input and generates three regulated rails: 12 V, 5 V, and 3.3 V to power the vehicle's telemetry sensors, network supervisor, and auxiliary embedded subsystems. Total output capability is approximately 124 W across all rails, with reverse-polarity protection, TVS surge clamping, per-rail current limiting, and MCU-supervised rail control built in.

Baja is transitioning to a data-driven development workflow, with increasing reliance on onboard telemetry and distributed sensing to tune vehicle performance. As the sensor suite expanded, two electrical needs became critical: reliable power distribution and low-noise, well-regulated voltage rails for sensitive electronics.

Previously, subsystems were powered directly from the 12 V battery bus. This was insufficient for mixed-voltage electronics. Several boards require regulated 5 V and 3.3 V supplies and are sensitive to supply variation and noise. The PDB was developed to centralize conversion and distribution so each subsystem receives the correct regulated rail from a single, documented power architecture.

Power Architecture

• Total output capability: ~124 W continuous
• Input range: 9–12 VDC
• Output voltage tolerance: ±5% on all rails at full load
• Operating temperature: -10°C to +50°C

Each rail is generated by a dedicated switching stage with its own inductor, output capacitance, and feedback network. The buck-boost topology on the 12 V rail maintains regulation even when the battery sags below 12 V under load.

Input Protection

• Reverse-polarity MOSFET: Chosen over a series diode to minimize conduction losses at 6 A+ input current. A MOSFET's milliohm R_DS(on) dissipates far less power than a Schottky diode's forward drop.
• 40 V TVS surge clamping: Absorbs transient spikes from hot-plug events and inductive loads on the vehicle harness.
• Rail-level protective elements at regulator outputs prevent upstream faults and transients from propagating into logic and sensor rails.

Distribution and Switching

• High-side switches (HSS_12V, HSS_5V) provide MCU-controlled load distribution with overcurrent protection.
• Per-rail fusing for additional fault-current limiting.
• Rail status LEDs and test points on all rails (12V, 5V, 3V3, GND) for rapid bench bring-up and field debugging.

Control and Telemetry

An on-board STM32F405 supervises rail behavior through:

• Enable lines (EN_12V, EN_5V) for software-level startup sequencing
• Current-sense feedback (12V_IS, 5V_IS) for load monitoring
• Voltage-sense feedback (12V_VS, 5V_VS) for rail health verification
• Heartbeat output for rapid "board alive" verification during bring-up

A CAN bus interface (transceiver with common-mode choke, termination, and ESD protection on CAN_P/CAN_N) transmits power telemetry to the CAN network for real-time monitoring and post-session analysis.

Mechanical

• Board size: 80 × 100 mm
• 2-layer stackup, optimized for small-batch fabrication cost.

Schematic Organization

The schematic is partitioned by function so each block can be reviewed independently and debugged in isolation:

• MCU + CAN + I/O: Microcontroller, CAN transceiver, test points, and heartbeat indicator
• Line Regulation and Distribution: Battery input protection, rail enable/control, current/voltage sense, and high-side switch blocks
• 5V Regulator: Switching regulator, compensation network, and MOSFET/inductor/output filter
• 12V Regulator: High-power switching stage, dual gate-drive/power stage, and feedback/sense network
• 3.3V Regulator: Local buck stage for logic/MCU rail (3V3_STM_PWR)

PCB Floorplan

The PCB is physically zoned by function: 12 V regulation, 5 V regulation, 3.3 V regulation, protection, MCU, CAN, and HSS distribution, to minimize interference between high-current switching loops and sensitive control/communication circuitry.

Layout priorities:

1. Keep switching loops compact (MOSFET–driver–inductor–capacitor)
2. Keep CAN protection and choke close to connector entry
3. Maintain easy probe access to test points and key nets

• Power electronics design: Switching regulator selection, inductor/capacitor sizing, feedback loop compensation
• Circuit protection: TVS selection, MOSFET-based reverse polarity, high-side switch overcurrent limiting
• Embedded integration: STM32 ADC signal conditioning, CAN bus communication, software-controlled rail management
• PCB design: High-current 2-layer layout, functional zone partitioning, thermal management, design-for-test
• Systems thinking: Translating vehicle-level electrical needs into a documented, testable board-level architecture

The board is currently in validation. Planned improvements for the next revision include:

• NTC thermistor for on-board temperature monitoring
• Battery state-of-charge estimation