Q1 MOSFET Replacement Notes
Summary
Q1 was replaced with a BSS138 N-channel MOSFET placeholder to preserve the intended BATTERYCUTOFF switching role from the image-derived schematic.
Original BJT mapping assumption
- Original Q1 was
MMBT3904LT1G NPN BJT.
- Original/approved functional mapping from the BATTERYCUTOFF circuit:
- BJT Base -> MOSFET Gate
- BJT Emitter -> MOSFET Source
- BJT Collector -> MOSFET Drain
Implemented MOSFET connectivity
Q1:G -> BATTERYCUTOFF net, shared with the S1/R8 side of the cutoff control network.Q1:S -> GND.Q1:D -> VCC, representing the collector/R8/VCC side requested in the replacement plan.
Uncertainties to review before production
- The source schematic image was blurry and image-derived; confirm whether Q1 should be an N-channel MOSFET.
- Confirm whether a BSS138-class MOSFET is electrically appropriate for the actual load/current.
- Confirm physical pin mapping, footprint orientation, and symbol orientation for the selected MOSFET.
- Confirm whether the drain should connect directly to
VCC or to a separate collector/load node tied to VCC through R8 in the original CAD.
Production recommendation
Treat Q1 as a placeholder until the original BOM, clearer schematic, or designer intent confirms the exact MOSFET MPN, pinout, and orientation.