Portable device power system solution based on ATmega 16L microcontroller

In response to the growing demand for power systems in portable devices, a power system solution based on a microcontroller as the central control unit has been proposed. This system utilizes a high-performance, low-power ATmega16L microcontroller as the core for battery detection and control. It integrates a charging and discharging circuit, a DC/DC converter, an external adapter, and a lithium battery pack to create a highly flexible and fully functional power supply system. As technology advances, portable devices are becoming increasingly popular due to their convenience in both work and daily life. However, they also place higher demands on internal power systems. These devices typically require power supply through both the main power adapter and the battery, along with charge/discharge control, battery state estimation, and compatibility with embedded motherboards. They must also be compact, lightweight, and energy-efficient. While existing power solutions for notebooks and mobile phones are mature, they often lack adaptability for more specialized portable applications. Given these challenges, there is a clear need for a more powerful and versatile power system that can meet the requirements of general-purpose portable devices. ### 1. Overall Design of the Power System The system uses a microcontroller as the central unit for monitoring and controlling various components, including the power adapter, battery pack, charge/discharge module, and DC/DC converter. The overall block diagram is illustrated in Figure 1. The voltage, current, and temperature of the battery pack are sampled and sent to the microcontroller via A/D conversion circuits. As the central processing unit, the microcontroller continuously monitors the battery’s performance and status. It controls the high-power switch based on these parameters, enabling automatic switching between the external adapter and the internal battery when needed. With the external adapter, both normal power supply and battery charging can be achieved. Additionally, the system includes an RS-232 interface for communication with the embedded motherboard, allowing the power status to be displayed on the host computer. To support the ATX power interface requirements of low-power embedded systems, the microcontroller simulates the PS_ON and PW-OK signals using its I/O ports, effectively providing ATX power functionality. Thanks to the use of a microcontroller, the system is highly adaptable, capable of implementing complex logic controls and easily expanding or upgrading in the future. ### 2. Battery Management #### 2.1 Battery Selection Currently, common rechargeable batteries include lead-acid, nickel-cadmium (NiCd), nickel-metal hydride (NiMH), and lithium-ion batteries. NiCd batteries are being phased out due to environmental concerns and limited cycle life. NiMH batteries suffer from the "memory effect" and have lower energy density. Lithium-ion batteries, on the other hand, offer advantages such as high energy density, no memory effect, long cycle life, and low self-discharge. For this system, Sanyo 18650 lithium-ion cells were selected. A 4S4P configuration provides a total capacity of 130 WH, ensuring sufficient endurance for portable use. #### 2.2 Core Control Chip The system employs Atmel’s ATmega16L microcontroller, known for its high performance and low power consumption. Based on RISC architecture, it features 16 KB of Flash, 512B EEPROM, 1KB SRAM, multiple timers, an 8-channel 10-bit ADC, USART, SPI, and a watchdog timer. Its operating voltage ranges from 2.7V to 5.5V, and it offers six power-saving modes to optimize power efficiency. The microcontroller interfaces with the battery, charger, and motherboard, supporting real-time data acquisition and control. #### 2.3 Charging Solution A LTC4006 chip from Linear Technology is used for charging, supporting up to 4A charging current for 2–4-cell Li-ion batteries. It includes built-in protection against overvoltage, overcurrent, and thermal issues. An external 19.8V DC adapter is used to power the system, allowing the battery to be charged and managed by the ATmega16L and LTC4006. The charging circuit is designed to minimize losses and provide accurate current regulation. #### 2.4 Estimating Battery Remaining Capacity Accurate State of Charge (SOC) estimation is crucial but challenging due to the nonlinear behavior of batteries. Common methods include the integration method, open-circuit voltage method, internal resistance method, and Kalman filter. However, each has limitations. The DC internal resistance method was chosen for its simplicity and effectiveness in portable applications. By measuring the voltage difference under load and dividing by the current, the internal resistance can be calculated, which correlates with the remaining battery capacity. Multiple discharge tests are performed to build a lookup table of resistance versus SOC, stored in the microcontroller’s Flash memory. This allows real-time SOC estimation during operation. #### 2.5 Charge and Discharge Display Unlike traditional systems that rely on LED indicators, this design enables real-time communication with the embedded motherboard. The user interface displays charging status via icons, such as a mains plug symbol during charging and a battery icon during discharge. When the remaining power drops below 10%, an alert is triggered, improving user awareness of the device's power status.

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