Current Sense Circuit for Low-Voltage Reverse Battery Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing current sense circuits are large due to the need for operational amplifiers, struggle with low voltage operation, and lack protection against battery reverse connection, especially in automotive applications.
Innovation Solution
A current sense circuit design using bipolar transistors and MOS transistors that operate at low voltages and protect against reverse connection by turning off when reversed, with negative feedback control to match VDS and provide immunity to noise and fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an operational amplifier is used for current sensing, then measurement precision is improved, but device complexity increases and circuit size increases
Solution Approach 1:
The patent extracts the current sensing function from a complex operational amplifier-based circuit and implements it using a simplified transistor configuration. The sensing transistor is integrated within the power MOSFET structure, eliminating the need for external operational amplifiers and reducing circuit complexity while maintaining sensing accuracy through direct voltage measurement across the sensing transistor.
Solution Approach 2:
The patent merges the current sensing function with the power MOSFET structure by integrating a sensing transistor within the same device. This combination eliminates separate sensing circuits and operational amplifiers, reducing overall circuit complexity and component count while enabling direct current measurement through the integrated sensing element.
2Measurement precision
If an operational amplifier is used for current sensing, then measurement precision is improved, but the area of the circuit increases
Solution Approach 1:
The patent implements a nested structure where the sensing transistor is integrated within the power MOSFET device itself. The sensing element is embedded in the same semiconductor structure as the power transistor, allowing current sensing functionality to be nested within the existing power device footprint without requiring additional external circuit area.
Solution Approach 2:
The patent combines the power switching function and current sensing function into a single integrated device structure. By merging these functions, the circuit area is reduced as no separate operational amplifier or external sensing circuitry is required, achieving both power control and current measurement within a compact integrated footprint.
3Measurement precision
If conventional current sense circuit is used, then current sensing is achieved, but protection against battery reverse connection is not provided
Solution Approach 1:
The patent applies preliminary anti-action by configuring the sensing transistor and associated circuitry to automatically block current flow when battery reverse connection is detected. The circuit is designed with inherent polarity sensitivity that prevents operation under reverse voltage conditions, proactively protecting against damage before it can occur.
Solution Approach 2:
The patent converts the potentially harmful effect of reverse connection into a protective mechanism. The circuit utilizes voltage polarity detection to trigger a protective state where current flow is blocked, transforming what could be a damaging condition into a safety feature that automatically prevents damage.
4Measurement precision
If conventional current sense circuit is used, then current sensing is achieved, but low voltage operation capability is insufficient
Solution Approach 1:
The patent employs parameter changes by designing the sensing transistor and associated circuitry to operate effectively at low voltage levels. The circuit parameters such as threshold voltages and biasing conditions are optimized for low-voltage operation, enabling accurate current sensing even when the supply voltage is reduced, thus improving energy efficiency and low-voltage performance.
Data Source
AI summary
A current sense circuit is provided. The circuit includes a current mirror circuit QN1, QN2, and diode-connected QP1, QP2, QP3, and QP4 with their bases connected together, stacking such that the diode-connected side (QN1, QP1, QP3) aligns and connecting the emitter of QP2 to the collector of QP4. Furthermore, the gates of MP1 and MP2 are connected to the collector of QN2 and QP2, respectively. Additionally, the source of MP1 is connected to the drain of MP3 via the source of MP2 and also connected to the source of a Sense MOS. Moreover, the emitter of QP4 is connected to the source of MP4 via R1, and the drain of MP4 is connected to the source (OUT terminal) of a Main MOS. Furthermore, the gates of MP3 and MP4 are connected to the emitters of QN1 and QN2.