Differential Voltage Detection Circuit for Body-Diode Leak Suppression
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Solution Overview
Problem
Conventional voltage detection circuits fail to accurately detect differential voltages of both positive and negative polarity in battery cells, such as fuel cells, due to leak currents caused by body diodes in MOS transistors, limiting their operational range and accuracy.
Innovation Solution
A voltage detection circuit with a differential configuration using paired detection capacitors and switches formed of P-channel and N-channel MOS transistors, where the substrate potentials of the transistors are controlled by maximum and minimum selectors to prevent leak currents, and a Zener diode is used to stabilize the substrate potentials in unstable regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional voltage detection circuits use MOS transistor body diodes for voltage detection, then the circuit structure is simple, but leak currents are generated that limit the detection range and accuracy for both positive and negative polarities
Solution Approach 1:
The detection circuit is segmented into separate P-channel and N-channel MOS transistor paths, each handling specific polarity detection. This segmentation allows independent optimization of each path to eliminate cross-polarity leak current interference, thereby improving measurement precision while maintaining reasonable device complexity
Solution Approach 2:
A substrate potential control circuit acts as an intermediary between the power supply and the MOS transistor substrates. This intermediary dynamically adjusts substrate potentials to match the detected voltage polarity, preventing body diode forward biasing and eliminating leak currents that would otherwise degrade voltage detection accuracy
2Adaptability or versatility
If the detection range is extended to cover both positive and negative polarities, then the versatility is improved, but leak currents from body diodes increase causing detection errors
Solution Approach 1:
The substrate potentials are made dynamic rather than fixed, automatically adjusting according to the detected voltage polarity. When positive voltage is detected, the P-channel substrate potential rises; when negative voltage is detected, the N-channel substrate potential falls. This dynamic adaptation enables wide polarity detection range while preventing body diode conduction and associated leak currents
Solution Approach 2:
The circuit changes the substrate potential parameter in response to voltage polarity changes. By modifying the substrate potential level dynamically, the circuit maintains MOS transistor operation in the saturation region without body diode forward biasing, thereby eliminating leak currents across the full detection range from negative to positive voltages
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 enables accurate detection of differential voltages over a wide range, suppressing leak currents and enhancing the operational range for both positive and negative polarities, thereby improving the accuracy and reliability of voltage detection in battery cell applications.
Implementation Method 1
a Zener diode is used to stabilize the substrate potentials in unstable regions
Data Source
AI summary
A voltage detection circuit includes two detection capacitors, which are paired and configured differentially, first to third detection switches, a drive part, a minimum selector and a maximum selector. The first detection switch is formed of a pMOS transistor, which opens and closes a path between one of the detection capacitors and an input node. The second detection switch is formed of an nMOS transistor, which opens and closes a path between the other of the detection capacitors and an input node. The third detection switch is formed of a series circuit of a pMOS transistor and an nMOS transistor, which open and close a path between two detection capacitors. The driving part turns on and off complementarily between the first and second switches and the third detection switch. The minimum selector applies a lower one of voltages of the input nodes as a substrate potential of the nMOS transistor. The maximum selector applies a higher one of the voltages of the input nodes as a substrate potential of the pMOS transistor.