Buck Boost Charging Circuit for USB Battery Packs
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Solution Overview
Problem
High voltage battery packs in mobile devices, such as computer tablets and digital SLR cameras, cannot be efficiently charged using standard USB power sources due to voltage mismatch, as most USB devices operate at 5V, which is insufficient for batteries with voltages ranging from 6-8.4V.
Innovation Solution
A battery charging circuit that operates in buck or boost mode to adapt voltage levels, allowing power to be stepped up or down between the input terminal and the battery or electronics, and includes a current sensor for monitoring and managing current flow, sharing power transistors to reduce space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a standard USB power source (5V) is used to charge a high voltage battery pack (6-8.4V), then the charging interface is universal and easy to operate, but the voltage is insufficient to charge the battery
Solution Approach 1:
The patent employs a buck-boost converter that dynamically adjusts the voltage parameter to transform the fixed 5V USB output into variable voltage levels (6-8.4V) required by the battery pack. The converter changes operating parameters including duty cycle and switching frequency to achieve the necessary voltage transformation ratio, resolving the contradiction between universal 5V interface and high voltage charging requirement
Solution Approach 2:
The buck-boost converter serves as an intermediary device between the USB power source and the battery pack. It receives power at 5V from the universal USB interface and transforms it into the required high voltage for battery charging, enabling compatibility between the low-voltage universal interface and high-voltage battery without requiring device-specific charging adapters
2Measurement precision
If separate power transistors are used for the current sensor and power train, then the sensing accuracy is improved, but the circuit space requirement increases
Solution Approach 1:
The patent merges the current sensor power transistor with the power train by utilizing the existing high-side power transistor (HS2) for dual purposes: both power switching and current sensing. The body diode of HS2 is configured to conduct during specific switching phases, allowing current measurement without requiring a separate sensing transistor, thus maintaining measurement accuracy while reducing circuit space
Solution Approach 2:
The high-side power transistor HS2 is designed with multi-functionality, serving both as a power switching element in the buck-boost converter and as a current sensing element. By configuring the body diode and control logic appropriately, the same transistor performs dual functions, eliminating the need for dedicated sensing transistors and reducing overall circuit component count and space requirements
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 charging of high voltage battery packs from standard USB sources by adjusting voltage levels, ensuring safe and efficient power delivery while minimizing circuit size, thus addressing the voltage compatibility issue and enhancing charging flexibility.
Implementation Method 1
The battery charging circuit may operate in buck mode (power stepped down) or boost (power stepped up) mode
Implementation Method 2
The battery charging circuit may operate in buck mode (power stepped down) or boost (power stepped up) mode
Implementation Method 3
the battery charging circuit may include a current sensor for sensing current in the one terminal and deriving an indication of current flow in the other terminal based on current flowing in the one terminal
Data Source
AI summary
Disclosed is a battery charging circuit having several operating modes include boost and buck mode, and forward and reverse mode. A power train and a current sensing block may share power transistors thus reducing the number of space-consuming power devices in the circuit. The current sensing block may indicate output current based only a sensed input current, and vice versa.