Lithium-ion batteries are widely used in portable electronics due to their high energy density, lightweight design, and rechargeable nature. However, charging these batteries requires careful voltage and current regulation to ensure safety, prevent overcharging, and maximize battery lifespan.
The 3.7V Smart Battery Charger Circuit is a compact and efficient solution designed to safely charge 3.7V lithium-ion batteries using a 5V input source, such as USB power or a standard adapter. The circuit employs a combination of active components, including the TL431 adjustable shunt regulator and the MJE13005 NPN transistor, to regulate the charging process effectively.
Component Details
S.no
Components
Value
Qty.
1.
Transistor
MJE13005
1
2.
Adjustable Shunt Regulator
TL431
1
3.
Resistor
1k, 680R, 470R, 47R
2,1,1,1
4.
LED
Red, Green
1,1
5.
Power Supply
5V DC
–
6.
Battery
3.7v
–
MJE13005 Pinout:
Circuit Daigram
Key Components
MJE13005 (NPN Transistor)
Controls current to charge the battery.
The transistor acts as a switch and regulator.
TL431 (Adjustable Precision Shunt Regulator)
Ensures voltage regulation for proper battery charging.
Adjusts its internal reference voltage for feedback control.
Resistors (47Ω, 680Ω, 1k, 470Ω)
Control current and set reference voltages.
Resistor values play an important role in feedback and limiting current.
LED Indicators
Red LED: Indicates charging status.
Green LED: Indicates charging completion or ready state.
3.7V Lithium-Ion Battery
The battery to be charged.
Input Power Source (5V DC)
Provides the required power for the charger circuit.
Working Principle
Input Power: The circuit takes 5V DC as the input to charge a 3.7V lithium-ion battery.
TL431 Feedback Regulation:
TL431 regulates the voltage and provides a stable reference.
It ensures that the output voltage does not exceed the safe charging voltage of 4.2V for the battery.
MJE13005 Control:
The NPN transistor (MJE13005) acts as a pass switch, controlling the charging current to the battery.
The transistor is turned ON/OFF based on the feedback provided by TL431.
Current Limiting:
The resistors (47Ω, 680Ω, and others) help limit the charging current to protect the battery.
LED Indicators:
When charging starts, the red LED lights up.
Once the battery is fully charged or the circuit detects the desired voltage level, the green LED turns ON, and the charging stops or reduces.
Battery Protection:
The circuit ensures the battery does not overcharge, extending battery life.
