Battery Cell Balancing Circuit Using Current Regulators
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Solution Overview
Problem
Conventional battery cell balancing circuits require extra pins for control, leading to increased costs and limited applicability for low voltage cells, and struggle to simultaneously balance neighboring cells due to conflicting current directions and high voltage requirements.
Innovation Solution
A cell balancing circuit using a current regulator to control a bypass path, allowing for simultaneous balancing of multiple cells without additional control pins, and utilizing switches with varying threshold voltages, including PMOSFET and NMOSFET, to manage conductance status independently of cell voltage, enabling balancing across a series-connected battery pack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated pin is used to control the bleeding control switch, then the cell balancing function is achieved, but the cost increases due to additional pins
Solution Approach 1:
The patent extracts the control function from a dedicated external pin and relocates it to an internal switch within the controller. This eliminates the need for an additional control pin while maintaining the cell balancing function. The internal switch is controlled by the controller's internal logic based on cell voltage measurements, achieving the same bleeding control without external pin intervention.
Solution Approach 2:
The controller is designed to perform multiple functions: it monitors cell voltages, determines unbalanced conditions, controls the bleeding switch, and manages battery charging/discharging. By integrating the bleeding control function into the existing controller architecture, the system achieves cell balancing without requiring dedicated control pins, thus reducing device complexity while maintaining reliability.
2Ease of manufacture
If a small voltage drop is used to control the bleeding control switch, then the circuit works with standard MOSFETs, but the threshold voltage requirement becomes too low (e.g., 1V) increasing cost
Solution Approach 1:
The patent introduces an intermediary voltage boosting mechanism between the voltage drop across the sensing resistor and the bleeding control switch gate. The controller measures the small voltage drop (e.g., 0.01V) across the sensing resistor and actively boosts this signal to a sufficient gate voltage (e.g., 4.5V) using its internal voltage regulation capabilities. This intermediary boosting stage allows the use of standard MOSFETs with normal threshold voltages while maintaining sensitivity to small voltage drops.
3Productivity
If the internal switch is turned on to conduct the bypass path, then the bleeding current flows through the resistor, but neighboring cells cannot be simultaneously balanced due to current direction conflicts
Solution Approach 1:
The patent segments the battery pack into individually controllable cell groups, with each cell having its own bypass path and bleeding control switch. The controller can independently manage each cell's balancing operation by selectively activating specific internal switches and bleeding switches based on which cells require balancing. This segmentation eliminates current direction conflicts between neighboring cells and enables simultaneous balancing of multiple cells.
4Adaptability or versatility
If the cell voltage is too low, then the gate-to-source voltage of the bleeding control switch cannot exceed the threshold voltage, but the circuit requires sufficient voltage to operate the switch
Solution Approach 1:
The controller performs preliminary voltage measurement and assessment before attempting to activate the bleeding control switch. It measures the cell voltage and determines whether it is sufficient to support switch operation. If the voltage is insufficient, the controller can take preliminary actions such as adjusting the reference voltage for comparison, modifying the bleeding current magnitude, or delaying the balancing operation until sufficient voltage is available, thereby ensuring reliable switch operation across different voltage conditions.
Data Source
AI summary
According to one embodiment of the invention, there is provided a cell balancing circuit used for balancing a cell. The cell balancing circuit includes a bypass path coupled to the cell, a current regulator coupled to the bypass path, and a bleeding control switch. The current regulator is operable for producing a current and for controlling a conductance status of the bypass path. The bleeding control switch conducts the bypass path in response to the current produced by the current regulator.