{"id":308,"date":"2026-04-01T22:48:46","date_gmt":"2026-04-01T22:48:46","guid":{"rendered":"https:\/\/mrsdprojects.ri.cmu.edu\/2026teamj\/?page_id=308"},"modified":"2026-04-02T00:09:23","modified_gmt":"2026-04-02T00:09:23","slug":"power-distribution-board","status":"publish","type":"page","link":"https:\/\/mrsdprojects.ri.cmu.edu\/2026teamj\/documents\/power-distribution-board\/","title":{"rendered":"Power Distribution Board"},"content":{"rendered":"\n

1 Design Overview<\/h2>\n\n\n\n

The Power Distribution Board (PDB) is the central power management hub for the planting mechanism on the Canopy reforestation robot. Powered from a MARBERO portable power station (110 VAC, 200 W continuous \/ 270 W surge), an isolated AC\/DC converter steps the input down to a 24 VDC main bus. The PDB routes this bus to the NEMA 23 stepper motor driver and the BLDC motor driver, while also generating regulated 9 V and 5 V rails for the microcontroller and encoder logic respectively. Reverse-polarity protection, fusing, and e-stop integration are incorporated on-board to ensure safe field operation.<\/p>\n\n\n\n

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2  Power Architecture<\/h2>\n\n\n\n

2.1  Input and Main Bus<\/h3>\n\n\n\n

The 110 VAC inverter output is converted to 24 VDC via an isolated AC\/DC converter. After accounting for downstream conversion losses, the practical continuous DC power budget is estimated at 150\u2013170 W. The 24 V rail is the primary distribution bus and serves as the supply for both high-power motor loads.<\/p>\n\n\n\n

2.2  Subsystem Power Rails<\/h3>\n\n\n\n
Rail<\/th>Load<\/th>Regulation<\/th>Peak Current<\/th><\/tr><\/thead>
24 V<\/td>NEMA 23 Stepper Motor Driver<\/td>Direct from bus (no additional regulation)<\/td>7.0 A<\/td><\/tr>
24 V<\/td>BLDC Motor Driver<\/td>Direct from bus (driver-capped at 30 A)<\/td>30 A<\/td><\/tr>
9 V<\/td>ELEGOO Mega R3 (MCU)<\/td>Mean Well N7809-1C DC\/DC buck (8\u201336 V \u2192 9 V)<\/td>0.1\u20130.3 A<\/td><\/tr>
5 V<\/td>Stepper encoder logic<\/td>XP Power isolated DC\/DC (6.5\u201336 V \u2192 5 V, 2 A)<\/td>1\u20132 A<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

The ELEGOO Mega R3 is isolated on its own 9 V rail (via the N7809-1C buck) to protect I\/O pins from noise on the high-current 24 V bus. The 5 V rail provides a clean logic supply for the stepper’s built-in encoder and may be extended to future sensors (e.g., flex force, soil moisture) for closed-loop control.<\/p>\n\n\n\n

2.3  Operating Modes<\/h3>\n\n\n\n

Because the combined peak draw of both motors exceeds the 200 W source capacity, the system enforces mutually exclusive operating modes. Simultaneous high-power operation is prohibited until power-station overload behavior is verified under stall conditions.<\/p>\n\n\n\n

Stepper Mode<\/p>\n\n\n\n

Stepper motor enabled, BLDC disabled. Used during horizontal positioning of the planting mechanism via the ball screw actuator.<\/p>\n\n\n\n

BLDC Mode<\/p>\n\n\n\n

BLDC driver enabled, stepper disabled. Activated once the auger is aligned with the planting location and drilling begins.<\/p>\n\n\n\n

3  Protection Circuitry<\/h2>\n\n\n\n

3.1  Reverse-Polarity Protection<\/h3>\n\n\n\n

A comparative thermal analysis was performed between a high-side P-MOSFET and an ideal-diode controller (LM5050MK-1\/NOPB) driving a low-RDS(on)<\/sub> N-MOSFET (NVMFS5C604NLAFT1G). At the worst-case continuous current of 4.2 A:<\/p>\n\n\n\n

P-MOSFET  (RDS(on)<\/sub> = 75 m\u03a9)<\/p>\n\n\n\n

Pcond<\/sub> = (4.2)\u00b2 \u00d7 0.075 \u2248 1.32 W
\u0394T = 1.32 \u00d7 R\u03b8JA<\/sub> \u2192 66 \u00b0C (best case) to 99 \u00b0C (worst case)
TJ<\/sub> = 91\u2013124 \u00b0C @ 25 \u00b0C ambient  \u2192  unacceptably high<\/strong><\/p>\n\n\n\n

N-MOSFET via LM5050  (RDS(on)<\/sub> = 10 m\u03a9)<\/p>\n\n\n\n

Pcond<\/sub> = (4.2)\u00b2 \u00d7 0.01 \u2248 0.18 W
\u0394T \u2248 0.18 \u00d7 50 \u2248 9 \u00b0C @ 25 \u00b0C ambient  \u2192  substantial thermal margin<\/strong><\/p>\n\n\n\n

The LM5050 ideal-diode controller was selected. It generates the necessary gate overdrive for high-side N-MOSFET switching, achieving robust reverse-polarity protection with significantly reduced steady-state conduction losses compared to a P-channel solution of equivalent footprint. 60 V P-channel devices inherently exhibit higher RDS(on)<\/sub> than comparable N-channel devices in the same package.<\/p>\n\n\n\n

3.2  Fusing<\/h3>\n\n\n\n

An 80 V \/ 15 A panel-mount fuse holder (F1<\/code>) is placed in series with the 24 V fused output path to the NEMA 23 stepper connector (J1<\/code>). A dedicated test point (J4, TP_NEMA_FUSED<\/code>) provides probe access at this node. A 40 V Schottky diode (D4<\/code>) provides back-EMF clamping on the fused 24 V rail to protect upstream circuitry during motor deceleration.<\/p>\n\n\n\n

3.3  E-Stop Integration<\/h3>\n\n\n\n

A two-position terminal block (J6, ESTOP_Block<\/code>) interrupts the 24V_SAFE<\/code> net when the e-stop circuit is opened. This net feeds the gate drive path of Q1<\/code> (N-MOSFET) and the NEMA motor connector, ensuring both high-power loads are de-energized on e-stop assertion. Ring-terminal connectors are required for reliable e-stop wiring; these were pending delivery as of the March 26 bringup milestone.<\/p>\n\n\n\n

3.4  Status Indicators<\/h3>\n\n\n\n