# PCB E-dolly (Component) ## Description 36 V Contactor Coil Driver with Safe Kill Loop, 3.3 V Logic, SPI IMU, 24 V/5 A Buck, and ESP32 IO12-Driven E-Stop MOSFET via Series PH2.0 Safety Connectors #E_STOP #MOSFET #PH2.0 #SAFETY ## Component Details - **Owner:** azertyuiopqsdfghjklm - **Created:** 1/22/2026 - **Last Updated:** 1/29/2026 - **Visibility:** Public - **Project Description:** 36 V contactor coil driver with safe kill input loop interface and 3.3 V logic control. - **R9 Role:** Base-emitter pull-down for Q1 ensuring coil off when IC1 output is high-Z or low. - **Contactor Coil Driver Topology:** Low-side NPN transistor (Q1 MMBT5551) with flyback diode (D2 UF4007) across coil between Net 1 (36 V) and Net 14 (Q1 collector). - **R8 Role:** Base/gate series resistor limiting drive from IC1 to Q1 (switching control). - **SAFE_IN Filter Components:** R3 (10k), C4 (100nF) to GND provide RC filtering; R4 (1k) provides series input protection and loop termination from CN3. - **CN3 Role:** 2-pin connector for external safe kill loop input (Safe Raw on pin 1, GND on pin 2). - **System Architecture:** ```mermaid flowchart TD ESP32["ESP32\n(IO12)"] --> E_STOP_IN1["PH2.0 Conn1\nE_STOP_IN1"] E_STOP_IN1 --> E_STOP_IN2["PH2.0 Conn2\nE_STOP_IN2"] E_STOP_IN2 --> Gate["MOSFET Gate\n(E_STOP_DRIVE)"] Gate -->|10kΩ Pull-up\n3.3V Rail| PU["3.3V Rail"] subgraph Power VB36["36V Bus"] --> Coil["Contactor Coil"] Coil --> Drain["MOSFET Drain\n(E_STOP_PATH)"] Drain --> Source["MOSFET Source"] Source --> GND["System Ground"] end ``` - **SAFE_IN Net Name:** Net 11 - **Domain:** Automotive - **Q1 Part Type:** Transistor - **Buck Converter Role (U1 MP2565):** Steps 36 V down to 3.3 V (Net 7) for logic and control electronics. - **Coil Flyback Strategy:** Standard flyback / freewheeling diode D2 from 36 V supply to transistor collector (Net 14) to clamp inductive kick on turn-off. - **Power Requirements:** Battery - **Logic Function (IC1):** Schmitt Trigger Inverter - **Net 1 Role:** High-side 36 V supply for contactor coil and buck converter input. - **Operating Voltage:** 36V - **Net 7 Role:** 3.3 V logic rail powering ESP32 and SN74LVC1G14 Schmitt inverter. - **IC1 Part Type:** Integrated Circuit - **D2 Part Type:** Diode - **SAFE_IN Role:** Safe kill input loop sensed via R3/R4 and filtered by C4 into Schmitt-trigger IC1. - **Mount Type:** PCB --- *Generated from [https://www.flux.ai/azertyuiopqsdfghjklm/pcb-e-dolly](https://www.flux.ai/azertyuiopqsdfghjklm/pcb-e-dolly)*