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This project presents the design of a Battery Low Voltage Cut-Off Circuit Using Transistor. The circuit continuously monitors the battery voltage through a resistor-divider sensing network and automatically disconnects the load when the battery voltage falls below a preset threshold.
A transistor-based threshold sensing stage controls a MOSFET, which performs the actual load disconnection. An LED provides an indication of the load-connected condition.
- Battery low-voltage detection
- Automatic load disconnection
- Transistor-based threshold sensing
- MOSFET-based load switching
- LED status indication
- Hysteresis to reduce switching chatter near the threshold
- Manual ON/OFF control
- Two-layer THT PCB design
The circuit consists of the following major sections:
- Voltage Sensing – R1 and R2 form a voltage divider to sense the battery voltage.
- Threshold Detection – Q1 acts as the transistor-based voltage threshold element.
- Hysteresis – R4 provides feedback to help prevent rapid switching near the threshold.
- Gate Driver – Q2 drives the MOSFET gate.
- Load Disconnect – Q3 is the power MOSFET used to disconnect the load.
- Status Indicator – LED1 and R7 indicate the load-connected condition.
- Filtering – C1 reduces noise at the sensing node.
- Manual Control – SW1 provides manual battery input ON/OFF control.
| Reference | Component | Value / Type |
|---|---|---|
| R1 | Resistor | 10 kΩ |
| R2 | Resistor | 10 kΩ |
| R3 | Resistor | 10 kΩ |
| R4 | Resistor | 100 kΩ |
| R5 | Resistor | 4.7 kΩ |
| R6 | Resistor | 10 kΩ |
| R7 | Resistor | 1 kΩ |
| Q1 | NPN Transistor | Small-signal |
| Q2 | NPN Transistor | Small-signal |
| Q3 | N-MOSFET | Logic-level |
| D1 | LED | Green |
| D2 | Protection Diode | As selected in schematic |
| C1 | Capacitor | 1 µF |
| SW1 | Switch | SPST |
| J1 | Battery Connection | 2-pin |
| J2 | Load Connection | 2-pin |
The PCB is designed as a two-layer board using through-hole components. The sensing section is kept separate from the high-current battery/load path. Wider traces are used for the power path, while narrower traces are used for signal and control connections.
The PCB design includes:
- Front copper layer (F.Cu)
- Bottom copper layer (B.Cu)
- Through-hole components
- Ground return/ground zone
- Short MOSFET gate-drive connection
- Wider battery/load traces
- Board outline on the Edge.Cuts layer
This folder contains the eSim/KiCad project files required to open and continue the design:
- Schematic file (
.kicad_sch) - PCB layout file (
.kicad_pcb) - Project file (
.kicad_pro) - Supporting documentation
- PCB design screenshots and verification files
The design is checked using:
- Electrical Rules Check (ERC)
- Design Rules Check (DRC)
- PCB layout inspection
- 3D PCB viewer
A low-voltage cut-off stage is useful in battery-powered systems where excessive battery discharge needs to be prevented. Possible applications include:
- Portable electronic devices
- Battery-powered systems
- Solar power systems
- UPS/backup systems
- Battery management and protection stages
The objective of this project is to design and document a simple, practical battery low-voltage protection circuit and implement it as a complete PCB using eSim/KiCad.
- eSim
- eSchema
- KiCad PCB Editor / Pcbnew
- ngspice (for simulation, where applicable)
eSim Semester Long Internship – Autumn 2026 Submission Task 7