In the world of DIY electronics, building practical, functional systems is one of the most rewarding activities. A battery charger is an essential component in many DIY projects, and having control over the design allows you to optimize it for specific needs. In this project, we will build a 12V battery charger using the ISL6259AHRTZ, an integrated circuit designed to efficiently manage the charging of lithium-ion (Li-ion) or lithium-polymer (LiPo) batteries.
The ISL6259AHRTZ is a versatile and highly efficient chip designed to charge 1-cell Li-ion or LiPo batteries. It integrates multiple features such as programmable charge current, charging termination, overvoltage protection, and thermal shutdown, making it ideal for building a smart and reliable battery charging system. We’ll dive into the circuit design, components needed, and step-by-step instructions for assembling the battery charger.
Overview of the ISL6259AHRTZ
The ISL6259AHRTZ is a highly integrated battery charge management IC from Intersil. It is designed specifically for portable applications like mobile devices, handheld electronics, and even small robotics, where a 1-cell Li-ion or LiPo battery is used for power. The chip incorporates several key functions in one package, which simplifies the design and reduces component count.
Some key features of the ISL6259AHRTZ include:
● Constant current/constant voltage (CC/CV) charging: Ensures the battery is charged in a safe manner by first supplying a constant current and then switching to constant voltage once the battery voltage reaches the pre-set charging threshold.
● Charge current control: The charging current can be adjusted using an external resistor, allowing the user to customize it according to the battery’s capacity and requirements.
● Charge status indicators: Provides useful feedback through its LED indicators, showing whether the battery is charging, fully charged, or not charging.
● Overvoltage and overtemperature protection: The chip automatically disables charging when the battery reaches an overvoltage condition or when the temperature exceeds a safe limit, ensuring the system operates within safe parameters.
● Thermal shutdown: This feature protects the circuit from excessive heat by stopping the charging process if the chip exceeds safe operating temperatures.
With these features, the ISL6259AHRTZ offers an excellent platform for designing a reliable and safe 12V battery charger for lithium-based cells.
Project Objective
In this project, we will use the ISL6259AHRTZ to design and build a compact 12V battery charger circuit. This charger will be capable of safely charging a single-cell 12V Li-ion or LiPo battery, providing the necessary current and voltage for efficient and safe charging. The circuit will include charge status indicators, overvoltage and overcurrent protections, and be powered by a DC input suitable for home or workshop applications.
Components Required
ISL6259AHRTZ – The main battery charge management IC.
Lithium-ion or Lithium-polymer battery (1-cell, 3.7V nominal) – The battery to be charged.
Resistors – To set the charge current and other parameters.
Capacitors – To filter voltage and ensure smooth operation.
Diode (e.g., 1N5819) – For reverse current protection.
LEDs – To indicate charge status (charging, full, or no charge).
Inductor (e.g., 10µH) – For efficient power conversion.
MOSFET (e.g., IRLZ44N) – For power switching and current control.
DC Power Supply (12V) – To power the charger.
Heat sink – For thermal dissipation if needed, to ensure the system does not overheat during charging.
PCB or breadboard – For assembling the components.
Connectors – To provide connections to the battery and power source.
Circuit Design
Power Supply Input
The first stage of the circuit design involves the power supply. The charger will be powered by a 12V DC input, which is commonly available from various power adapters. This 12V input will power the ISL6259AHRTZ and other circuit components.
A diode (1N5819) is placed in series with the input to protect the circuit from reverse voltage. This ensures that the system does not get damaged if the power supply is incorrectly connected.
Charging Circuit
The heart of the charging circuit is the ISL6259AHRTZ. This IC manages the charging process, ensuring that the battery is charged using a constant current (CC) phase until it reaches the target voltage, and then switches to constant voltage (CV) mode. The charging current is set by selecting an appropriate external resistor connected to the chip.
The key pins on the ISL6259AHRTZ include:
● BAT (Pin 2): Connected directly to the positive terminal of the battery.
● PGND (Pin 5): Connected to the ground of the circuit.
● VC (Pin 6): The voltage at this pin will indicate the charging status.
● ISET (Pin 7): This is the pin used to set the charging current through an external resistor.
● CHRG (Pin 10): This pin is used to connect an LED that will indicate the charge status. When the battery is charging, this LED will light up, and when charging is complete, it will turn off.
Inductor and Capacitor
To ensure smooth charging, an inductor (e.g., 10µH) and a set of capacitors are added to the circuit. These components will help filter out noise and smooth voltage fluctuations, ensuring a stable charging process. Capacitors should be placed close to the IC for optimal performance.
Charge Status Indicators
To visually represent the charging process, we add two LEDs:
● Charging LED (LED1): Lights up when charging is in progress.
● Full LED (LED2): Lights up when the battery is fully charged.
These LEDs are driven by the CHRG pin of the ISL6259AHRTZ. The charging LED will glow when the battery is charging, and the full LED will glow once the battery reaches full charge and the system switches to CV mode.
Thermal and Overvoltage Protection
The ISL6259AHRTZ includes built-in thermal shutdown and overvoltage protection, but additional thermistors or heat sinks may be added if needed. These components will ensure that the system remains safe under high temperatures or excessive voltage conditions.
Assembling the Circuit
Prepare the PCB or Breadboard: Start by placing the ISL6259AHRTZ on the PCB or breadboard. Make sure to route the pins for power, ground, and signal connections carefully.
Connect the Power Input: Connect the 12V DC power source to the input of the circuit. Place the diode in series to prevent reverse current.
Set the Charge Current: Use an appropriate resistor to set the charge current based on your battery's specifications. Connect this resistor to the ISET pin of the ISL6259AHRTZ.
Add Inductors and Capacitors: Place the inductor and capacitors as shown in the datasheet. These will help ensure stable charging and smooth operation of the IC.
Connect the Battery: Connect the positive terminal of the battery to the BAT pin of the ISL6259AHRTZ. The negative terminal connects to the ground.
Install LEDs: Place the LEDs on the CHRG pin to indicate the charge status.
Test the Circuit: Once everything is connected, power up the circuit. The charging LED should light up, and once the battery is fully charged, the full LED should indicate that the charging process is complete.
Testing and Calibration
After assembly, it is crucial to test the charger to ensure it works correctly. Connect a 12V Li-ion battery and observe the charging process. The charging LED should illuminate when the charger is connected, and it should turn off when the battery is fully charged.
Use a multimeter to check the voltage at the battery terminals during charging. The voltage should gradually rise as the charger operates in CC mode and switch to CV mode once the battery reaches the target voltage (typically 4.2V for a 3.7V nominal Li-ion cell).
Conclusion
Building a 12V battery charger with the ISL6259AHRTZ is a highly rewarding project that teaches valuable concepts in power electronics and charging systems. The charger is efficient, safe, and capable of charging a single-cell Li-ion or LiPo battery with features like thermal and overvoltage protection, charge status indicators, and adjustable current settings. This project can be adapted for use in various DIY electronics projects, from portable devices to robotics, where reliable battery charging is essential.