Charge Control Circuit for Boosting USB Voltage to Charge Two-Cell Li-Ion Batteries
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Solution Overview
Problem
Existing charge circuits for mobile electronic devices, such as those using USB power supplies, are unable to generate the higher voltage required for charging two-cell lithium-ion secondary batteries like those in digital video cameras, as they rely on step-down DC-DC converters that cannot produce voltages above the input voltage, typically limited to around 5 volts.
Innovation Solution
A charge control circuit that includes a comparator circuit, transistors, and control circuits to manage a boost DC-DC converter, allowing it to switch between constant-current and boost modes based on the battery voltage, effectively increasing the input voltage from a USB power supply to the required level for charging two-cell lithium-ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a step-down DC-DC converter is used to charge the secondary battery, then the circuit can operate with simple configuration, but the output voltage cannot exceed the input voltage (limited to about 5 volts from USB power supply)
Solution Approach 1:
The patent inverts the conventional step-down converter approach by using a step-up (boost) DC-DC converter instead. This allows the output voltage to exceed the input voltage, enabling charging of two-cell lithium-ion batteries requiring 8.4V from a 5V USB power supply. The boost converter topology fundamentally reverses the voltage transformation direction to solve the voltage limitation problem.
Solution Approach 2:
The patent implements dynamic switching between two operational modes: constant current charging mode and boost operation mode. The control circuit dynamically selects the appropriate mode based on real-time voltage comparison between the secondary battery and input power supply, allowing the system to adapt its charging strategy to optimize both voltage output and charging efficiency.
2Power
If a boost DC-DC converter is used to increase output voltage above input voltage, then the voltage requirement for two-cell batteries can be met, but the device complexity increases due to additional control circuits and switching mechanisms
Solution Approach 1:
The patent merges the voltage comparison function and charging mode control function into an integrated control system. The comparator circuit directly feeds its output to the control logic that manages both the constant current charging and boost operation modes, eliminating the need for separate control circuits and reducing overall system complexity despite the enhanced functionality.
Solution Approach 2:
The control circuit automatically determines the appropriate charging mode by comparing the secondary battery voltage with the input power supply voltage through the comparator circuit. This self-service mechanism eliminates the need for external control signals or complex microcontroller-based decision-making, simplifying the control architecture while maintaining intelligent adaptive charging capability.
3Productivity
If constant current charging is used when battery voltage is low, then charging efficiency is improved, but the voltage remains insufficient for two-cell batteries requiring higher voltage
Solution Approach 1:
The patent employs periodic mode switching between constant current charging and boost operation based on voltage thresholds. The system periodically evaluates the battery voltage against the input voltage through the comparator, and switches between charging modes accordingly. This periodic action ensures efficient charging at low voltages while transitioning to voltage boosting when needed, achieving both charging efficiency and voltage requirements over the charging cycle.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient charging of two-cell lithium-ion batteries by switching between constant-current and boost modes, ensuring the battery voltage is increased to the necessary level, even when the input voltage is lower, thereby addressing the voltage limitation of previous charge circuits.
Implementation Method 1
a boost DC-DC converter performs a boost operation
Data Source
AI summary
A charge control circuit includes a comparator circuit to compare a secondary-battery voltage with a comparison voltage corresponding to an input-power-supply voltage, a transistor to supply an input current to an inductor, a first control circuit to control the transistor, and a second control circuit to control second and third transistors to increase and decrease an inductor current, respectively, so that a boost DC-DC converter performs a boost operation. When the secondary-battery voltage is equal to or higher than the comparison voltage, the first and second control circuits turn on the transistor and perform switching of the second and third transistors complementarily, respectively. When the secondary-battery voltage is lower than the comparison voltage, the first control circuit controls the transistor so that the input current takes a predetermined value, and the second control circuit turns on and off the third and second transistors, respectively.