Bidirectional MOSFET Charge Control Circuit Leakage Reduction
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Solution Overview
Problem
Conventional charge/discharge control circuits for secondary batteries face issues with high leakage current when OFF and unstable operation due to limitations in gate voltage control and floating back gate states, leading to inefficient overcharge and overdischarge protection.
Innovation Solution
A charge/discharge control circuit using a single bidirectionally conductive field effect transistor with a control circuit, switch circuit, and transistors to monitor voltage and control the gate and back gate, reducing leakage current and ensuring stable operation by connecting the gate to source or drain voltage and the back gate to external terminals or power supplies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional enhancement mode N-channel MOSFET is used for bidirectional charge/discharge control, then the circuit can achieve bidirectional energization and interruption, but the leakage current increases and operation becomes unstable due to gate voltage limitations and floating back gate states
Solution Approach 1:
The patent divides the gate control function into two independent control paths: one for the main gate (controlling channel conduction) and one for the back gate (controlling threshold voltage). This segmentation allows independent optimization of each control function, enabling precise control of the MOSFET's ON/OFF states and threshold voltage to reduce leakage current while maintaining bidirectional control capability.
Solution Approach 2:
The patent introduces a back gate as an intermediary element between the control circuit and the main channel. By controlling the back gate voltage, the threshold voltage of the MOSFET can be adjusted, which indirectly controls the leakage current and stabilizes the OFF state without affecting the main gate's bidirectional control function.
2Loss of energy
If the gate voltage is controlled to reduce leakage current, then leakage current decreases, but the MOSFET may fail to maintain stable operation due to floating back gate states
Solution Approach 1:
The patent extracts the back gate function from the conventional MOSFET structure and makes it an independently controllable element. By separating the back gate control from the main gate control, the patent can independently manage the threshold voltage (via back gate) to reduce leakage while the main gate maintains stable switching operation, preventing floating state issues.
Solution Approach 2:
The patent dynamically changes the threshold voltage parameter by adjusting the back gate voltage. This parameter change allows the MOSFET to operate with reduced leakage current in the OFF state while maintaining stable operation, as the back gate voltage can be optimized to prevent floating states without compromising the main switching function.
3Device complexity
If a single bidirectionally conductive MOSFET is used for charge/discharge control, then device complexity is reduced, but control precision and reliability deteriorate due to inability to independently control gate and back gate
Solution Approach 1:
The patent makes the single MOSFET multi-functional by enabling independent control of both gate and back gate. This allows the same device to simultaneously perform bidirectional switching, leakage current reduction, and threshold voltage optimization, achieving high control precision without increasing the number of transistors.
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
The solution effectively reduces leakage current and stabilizes the operation of the charge/discharge control circuit, preventing overcharge and overdischarge by controlling the gate and back gate voltages, thereby enhancing the reliability of the battery device.
Implementation Method 1
an enhancement mode N-channel MOSFET 306 capable of bidirectional energization/interruption is connected in series to a negative terminal of a secondary battery 101
Implementation Method 2
A control circuit 102 detects a voltage of the secondary battery 101 and a voltage of the enhancement mode N-channel MOSFET 306
Data Source
AI summary
Provided is a battery device for controlling charge/discharge of a secondary battery by a single bidirectionally conductive field effect transistor, a charge/discharge control circuit with which a leakage current of the bidirectionally conductive field effect transistor is reduced to perform stable operation. The charge/discharge control circuit includes: a switch circuit for controlling a gate of the bidirectionally conductive field effect transistor based on an output of a control circuit for controlling the charge/discharge of the secondary battery; and two MOS transistors for preventing back-flow of a charge current and a discharge current. The first MOS transistor has a drain and a back gate which are connected to each other, and a source connected to a drain of the bidirectionally conductive field effect transistor. The second MOS transistor has a drain and a back gate which are connected to each other, and a source connected to a source of the bidirectionally conductive field effect transistor.