What is an MCU-equipped battery charger? Next-generation charging technology that achieves miniaturization, high efficiency, and long lifespan

MCU-equipped battery chargers precisely control charging profiles and protection functions such as OVP and OCP in a single chip. Specification changes are easy via firmware updates, and with Unifive, custom solutions tailored to specific applications are possible.

MCU-equipped battery chargers/chargers represent state-of-the-art charging technology that enables one-chip control of charging profiles (methods) and various protection functions such as OVP and OCP using a microcontroller (MCU).

Compared to conventional analog-controlled chargers, advanced digital control by an MCU achieves high-precision charging and enhanced safety, while also enabling flexible specification changes through firmware updates.

UNIFIVE's MCU-equipped charging solutions can be customized to meet customer applications, contributing to miniaturization, higher efficiency, and extended battery life.

What is an MCU? Basics of Microcontrollers

An MCU (Microcontroller Unit) is an ultra-compact computer that integrates a CPU, memory, and I/O on a single chip. It is widely embedded in products ranging from home appliances to industrial equipment, and in recent years has also been built into battery chargers to enable advanced digital control.

By performing control through software instead of conventional analog ICs or hardware circuits, functional integration and flexible control become possible.

In chargers with built-in MCUs, the MCU reads battery voltage, current, and temperature information in real time and adjusts to optimal charging current and voltage using software algorithms. This enables precise tracking of complex charging profiles for lithium-ion batteries and others, and allows various threshold values to be freely set and optimized for each battery.

Three Reasons Why MCU-Equipped Battery Chargers Are Chosen

1. Multi-functionality and System Integration

Battery condition diagnostics (voltage and temperature monitoring), charging control, communication with external devices, and protection controls such as overvoltage protection (OVP) and overcurrent protection (OCP) can all be integrated into a single chip.

This allows functions that previously required separate ICs or circuits to be handled by a single MCU, leading to reduced component count and greater flexibility in circuit design. The entire system can be simplified and integrated, ultimately improving reliability.

2. Flexible Specification Changes via Software

One of the greatest advantages of adopting an MCU is the flexibility to modify charging specifications. Since charging algorithms and profiles can be adjusted simply by rewriting software, it is easy to support new battery chemistries and optimize control parameters even after deployment.

For example, customization such as switching from standard CC-CV charging to a pulse charging method, or adjusting charging voltage and current thresholds to match battery manufacturer recommendations, can be achieved through firmware updates.

New features and improvements can be added without hardware changes, resulting in shorter development cycles and designs that are robust against future updates.

3. Multiple Protection Functions and Real-Time Monitoring

Because the MCU can process sensor information at high speed, it can execute multiple protection functions with high precision, such as overvoltage protection (OVP), overcurrent protection (OCP), and overtemperature protection (OTP).

When an abnormality is detected, it enables real-time protection, such as immediately stopping charging or performing a safe shutdown. In addition, since voltage, current, and temperature values during charging can be continuously recorded and communicated as monitoring logs, battery status monitoring and degradation prediction can also be performed with high accuracy.

Features of MCU-Equipped Battery Chargers

Custom Configuration of Protection Functions

Thresholds and operation delay times for various protections such as OVP (overvoltage protection), OCP (overcurrent protection), and OTP (overheat protection) can be freely configured according to the application.

With MCU control, fine adjustments can be made, for example, "At what voltage overvoltage is detected" and "How many milliseconds after detection the cutoff occurs". This enables optimal protection behavior according to the application, firmly protecting batteries and equipment while avoiding unnecessary shutdowns.

Automatic Control of Long-Duration Peak Current

Even when a large current is temporarily required depending on the load, the MCU can programmatically control the duration of the peak current. If the peak current continues to flow longer than the set number of seconds, the current is automatically reduced to the rated value to suppress overheating and component degradation.

For example, flexible current profiles can be implemented, such as "Allow up to 150% of the maximum output current for 5 seconds, then return to the normal current". This achieves both inrush current supply at startup and long life and safety.

Integrated Monitoring of Multiple Outputs

A single MCU can collectively monitor and control the output voltage and current of multiple channels. Conventionally, individual control circuits and feedback were required for each output system, but with an MCU, multiple channels can be managed simultaneously via software, enabling simplification of wiring and control systems.

By integrally monitoring all outputs and performing power distribution and balance control as needed, it also contributes to overall system efficiency optimization.

Temperature-Linked Fan ON/OFF Control

In chargers equipped with cooling fans, the MCU can automatically control fan rotation according to values from temperature sensors. For example, the fan can be turned ON when the internal temperature exceeds a certain threshold and turned OFF once sufficiently cooled, avoiding continuous operation.

By operating the fan only when necessary, this leads to noise reduction and energy savings, while also reducing dust intake.

External Transmission of Alarm Signals

When a power supply or battery abnormality is detected, the MCU can immediately output an alarm signal to external devices or systems. For example, if abnormally high temperature is detected inside the charger, the MCU notifies the facility monitoring system or a higher-level microcontroller, prompting prompt action such as load cutoff or user notification.

It is also possible to send detailed information via communication protocols according to the type of abnormality, enabling support for smart monitoring in the IoT era.

AC/DC Power Adapters — Desktop & Wall-Mount

In chargers equipped with an MCU, the MCU circuit is generally integrated on the low-voltage side (secondary-side circuit) inside the AC/DC Power Adapters — Desktop & Wall-Mount.

An AC/DC Power Adapters — Desktop & Wall-Mount consists of a primary-side circuit that rectifies and steps down commercial AC power to obtain the required DC output, and a secondary-side control circuit that charges the battery with an appropriate voltage and current. The MCU is mainly placed in the latter control circuit section, where it monitors the battery voltage and current while driving the DC-DC converter and switching elements for charging.

Specifically, in an isolated AC/DC Power Adapters — Desktop & Wall-Mount, the MCU is placed on the transformer-isolated secondary side. From there, it may control the primary-side switching IC via a photocoupler, or directly control the secondary-side synchronous rectification and DC output stage. This enables digital feedback control across the primary and secondary sides, allowing the MCU to regulate the output voltage and current as intended.

In the digital control method recommended by UNIFIVE, the MCU is mounted at an appropriate location on the adapter board and connected to the necessary sensing circuits (voltage and current sensors) and gate driver circuits. This makes it possible to add the benefits of digital control without significantly changing the conventional circuit configuration, enabling highly accurate control and customization of charging profiles.

Main Parameters Adjustable via MCU Software

In battery chargers equipped with an MCU, the following charging control parameters can be finely configured and adjusted via software. Each parameter can be customized to optimal values according to the battery type and application, improving charging safety and efficiency.

Pre-charge Switching Voltage

This is the voltage threshold at which charging switches from pre-charge to main charge. For batteries that have been deeply discharged and whose voltage has dropped significantly, it is necessary to first charge slowly with a low current to reactivate the cells.

With MCU control, thresholds such as "End pre-charge and transition to fast charging when the battery voltage exceeds XX V (e.g., approximately 3.0 V for lithium-ion batteries)" can be programmed.

Pre-charge Current

This is the preliminary charging current applied in the initial stage to a deeply discharged battery. Typically, charging begins slowly at a low current of about 10% of the full-charge current (around 0.1C). For example, a 2000 mAh battery would be pre-charged at approximately 200 mA (0.1C).

Post-charge Start Voltage / Post-charge Current

When the main charging phase nears completion, a very low-current top-off (trickle charge) may be applied to maximize capacity or balance the cells. The voltage point at which this transition begins and the current value can be defined by the MCU.

Charge Completion Voltage

This is the target voltage (float voltage) used to determine when the battery is fully charged. For lithium-ion batteries, approximately 4.2 V per cell is typically set as the charge completion voltage, but the MCU allows this termination voltage to be freely adjusted.

For example, it can be adjusted to a slightly lower voltage to prioritize safety and extend lifespan, or to a slightly higher voltage for fast charging applications.

Recharge Voltage

This is the voltage threshold at which automatic recharge begins. After reaching full charge once and terminating charging, the battery voltage gradually decreases over time due to standby current consumption of the device. When the battery voltage drops to this recharge threshold, charging automatically resumes.

Battery Detection Time

This is a time parameter used to detect the presence and condition of the battery. When a battery is connected to the charger, the MCU first measures the terminal voltage or applies a small test current to determine whether the battery is properly connected.

Output Overvoltage Protection (OVP) / Output Overcurrent Protection (OCP)

These are protection thresholds for the voltage and current on the charger output side. If the values exceed the set limits due to an abnormal condition during battery charging, the MCU immediately limits or shuts off the output to prevent battery overvoltage (overcharging) or circuit damage.

Safety Timer Duration / Pre-Charge Timer

These refer to the overall charging timeout (safety timer) and the timeout dedicated to the pre-charge stage. If charging is not completed within the specified time or the battery voltage does not recover to the threshold, the system stops operation as a safety measure, considering it an abnormal condition.

As described above, an MCU-equipped battery charger can comprehensively control all charging parameters through software. By optimizing various thresholds, timers, and current/voltage values, it is possible to achieve a customized charging profile tailored to the battery type and condition, enabling both fast charging and safety while extending battery life.

Typical Charging Control Methods

Chargers equipped with an MCU can implement various charging methods through software, allowing the optimal control algorithm to be selected according to the application.

Constant Current / Constant Voltage Control (CC-CV Method)

This is the standard method used for lithium-ion batteries. First, during CC (constant current) charging, the battery voltage gradually rises. When it reaches the specified maximum voltage (charge termination voltage), the process switches to CV (constant voltage) charging, continuing to charge while the current gradually decreases. Charging ends when the current drops to a sufficiently low level during the CV stage.

This method offers the advantage of safe and relatively fast full charging. With MCU control, the CC current value, CV voltage value, and termination current can be flexibly configured.

Pulse Charging & Refresh Charging

Pulse charging uses intermittent current pulses as the name suggests and is effective for lead-acid batteries. By applying high-voltage pulses, it removes lead sulfate crystals (sulfation) accumulated inside the battery, helping restore capacity and reduce internal resistance.

On the other hand, for nickel-metal hydride (Ni-MH) and nickel-cadmium batteries, refresh charging is used to mitigate capacity loss caused by the memory effect by discharging the battery once and then recharging it. With MCU control, these complex patterns can also be executed through software.

Summary: Leave next-generation charging solutions realized by MCU-equipped chargers to the proven experts at UNIFIVE

MCU-equipped battery chargers/chargers are a key technology that dramatically enhances charging precision, safety, and operational flexibility.

UNIFIVE provides charging solutions optimized to meet customer requirements through multi-layer protection design based on extensive experience and firmware customization support. From the development of compact, high-performance AC/DC Power Adapters — Desktop & Wall-Mount to the implementation of special charging profiles, please feel free to contact us.