3.7V Battery Charger Circuit 1s-2s TL431 auto off
Build a 3.7V battery charger circuit 1S – 2S using TL431 for high-precision auto cut-off. Step-by-step guide, schematic, components, working principle, and safety tips included.
What is a 3.7V Battery Charger Circuit?
The circuit of a 3.7V battery charger is made to protect the charging of the lithium-ion batteries by managing the
voltage and current. Li-ion cells can be overcharged, and this may decrease the battery life or lead to safety issues.
The charger of the TL431-based has a precision voltage reference and thus the output voltage is kept constant and
disconnects charging when the battery attains full voltage.
This circuit can accommodate 1S (single cell) or 2S (two cells in series) lithium-ion packs, and a voltage of around
4.2V/cell. There is an auto cut-off feature that makes sure that the batteries are not overcharged.
3.7v battery charger
The circuit 1S 2S TL431 high precision auto cut-off 3.7V battery charger is a necessary DIY electronics project to safely charge lithium-ion batteries. This circuit, with a TL431 shunt regulator, offers correct voltage regulation, automatic cut-off on full charge of the battery, and avoids excessive charge. It may be set to single-cell (1S) or two-cell (2S) battery, and may apply to small electronics, DIY projects, and portable projects. This guide will describe the main characteristics, the principle of operation, the list of all the components, the step-by-step construction, the test procedure, the usability, and the safety precautions. At the conclusion, you will have a fully operating 3.7 V charger battery with a definite auto cut-off to charge batteries safely and in an effective manner.
Features of TL431-Based Charger Circuit
High Precision Voltage Regulation
- TL431 provides a 2.5V reference voltage that can be amplified using a resistor network to achieve a precise output voltage for charging.
- Ensures stable constant voltage during the charging process.
Auto Cut-Off Function
- Automatically stops charging when battery voltage reaches the pre-set limit.
- Prevents overcharging and prolongs battery lifespan.
Supports 1S and 2S Li-ion Batteries
- Can charge single or dual-cell packs.
- Easily adjustable by resistor selection in the TL431 network.
Components Needed
TL431 Shunt Regulator
- Acts as a precision voltage reference and comparator for the cut-off function.
MOSFET or Transistor
- Used as a switching device to control current flow to the battery.
- Recommended: IRF540N, 2N7000, or similar low-voltage MOSFETs.
Resistors and Capacitors
- Set charging voltage and current limits.
- Filter capacitors reduce voltage ripples.
Battery Connectors
- Connect the battery safely to the circuit using proper polarity connectors.
Optional LED Indicators
- Red LED for charging
- Green LED for full battery
Working Principle of the Charger Circuit
Constant Voltage Charging
When the battery is connected, the circuit regulates current initially, then maintains a constant voltage until the The battery is nearly full.
Auto Cut-Off Mechanism
- TL431 monitors battery voltage.
- When voltage reaches the pre-set cut-off (e.g., 4.2V per cell), TL431 turns off the MOSFET, stopping the current flow.
Step-by-Step Circuit Assembly
Preparing the Power Source
- Use a DC adapter that can provide 5–6V for 1S or 8–9V for 2S with current limit according to battery capacity.
Connecting TL431 and MOSFET
- Connect TL431 reference input via resistor divider to battery terminals.
- MOSFET drain/source controls the charging path.
Setting the Cut-Off Voltage
- Adjust resistor values to achieve 4.2V per cell at the TL431 feedback pin.
- Measure with a multimeter before connecting the battery.
Testing the Charger Circuit
- Connect a dummy load or test battery.
- Measure charging voltage and current.
- Verify auto cut-off functionality at full charge.
Applications of 3.7V Battery Charger Circuits
- DIY battery packs
- Portable electronics
- Power banks
- Small robotic devices
- Rechargeable LED lights
Safety Precautions
- Always verify battery polarity before connecting.
- Do not exceed the recommended current or voltage.
- Use fuses or PTC resettable fuses for safety.
- Avoid charging unattended.
- Ensure good ventilation to prevent overheating.
Troubleshooting Common Issues
- Battery not charging: Check power source and MOSFET connections.
- LED indicator not working: Verify LED orientation and resistor values.
- Battery overcharges: Recheck TL431 voltage divider values.
Frequently Asked Questions - 3.7V Battery Charger Circuit 1s-2s TL431 auto off:
What is a 3.7V battery charger 1S – 2S TL431?
A charger circuit using TL431 for precise voltage regulation with auto cut-off for 1S or 2S lithium-ion batteries.
Can I use it for a single-cell battery?
Yes, it supports 1S battery charging with precise voltage control.
Can it charge two cells in series?
Yes, 2S configuration is supported with adjusted voltage divider values.
What is the role of TL431?
TL431 acts as a precision voltage reference and comparator for auto cut-off.
Do I need a MOSFET?
Yes, it controls current flow to the battery and switches off when fully charged.
How do I set the cut-off voltage?
Adjust resistor values in the TL431 voltage divider to achieve 4.2V per cell.
Is it safe for beginners?
Yes, if you follow safety precautions and double-check connections.
Can I use it with high-capacity batteries?
Yes, but ensure current rating of MOSFET and power source is sufficient.
Do I need LED indicators?
Optional, but helpful for showing charging status.
How do I maintain the charger circuit?
Keep it clean, check connections, avoid moisture, and store safely.
