Power Switch Current Sensing Across Overcurrent and Short Circuit
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Solution Overview
Problem
Existing power switch circuits face inaccuracies in over current protection due to voltage differences and oscillations during short circuit protection, leading to errors in current sensing and output voltage control.
Innovation Solution
A power switch circuit design that utilizes two sensing circuits, a first current sensing circuit for over current protection and a second for short circuit protection, switched based on output voltage levels, with matching transistors and isolation circuits to maintain accurate current sensing across varying voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single sensing circuit is used for both over current protection and short circuit protection, then the device complexity is reduced, but the measurement precision of current sensing deteriorates due to voltage differences and oscillations during short circuit protection
Solution Approach 1:
The sensing function is segmented into two separate sensing circuits: a first sensing circuit for normal over-current protection and a second sensing circuit for short-circuit protection. Each circuit is optimized for its specific operating condition, with the second circuit designed to eliminate voltage offset errors that occur during short-circuit events. This segmentation allows each circuit to maintain high measurement precision for its designated function without compromising the other.
Solution Approach 2:
The system dynamically switches between the first and second sensing circuits based on the operating condition. A selecting circuit determines which sensing circuit to use based on voltage levels and protection requirements. This dynamic switching ensures that the appropriate sensing circuit is active at any given moment, maintaining measurement precision across all operating conditions while managing device complexity through intelligent control.
2Reliability
If the output voltage drops to close to 0V during current limitation, then the short circuit protection is activated, but the measurement precision of current sensing deteriorates due to voltage offset caused by the current limit circuit
Solution Approach 1:
A second sensing circuit is introduced as an intermediary solution specifically for short-circuit conditions. This circuit bypasses the voltage offset issues that plague the first sensing circuit when output voltage approaches 0V. The second sensing circuit uses a different sensing topology that remains accurate even under extreme voltage conditions, acting as a mediator that provides reliable current measurement when the primary sensing method fails.
Solution Approach 2:
The sensing approach changes parameters based on operating conditions. During normal operation, the first sensing circuit uses standard voltage-based sensing. During short-circuit conditions when output voltage drops to near 0V, the system switches to the second sensing circuit that employs different sensing parameters and topology, eliminating the voltage offset error that would otherwise occur and maintaining measurement precision across the full voltage range.
3Measurement precision
If two separate protection circuits are used for over current protection and short circuit protection, then the measurement precision of current sensing is improved, but the device complexity increases and output voltage oscillates during switching
Solution Approach 1:
The two sensing circuits share common components and infrastructure, including the selecting circuit that routes between them, shared power supply connections, and common output stages. This merging approach allows the system to maintain two specialized sensing circuits for high measurement precision while reducing the overall complexity increase that would result from completely separate circuits. The shared architecture minimizes redundant components and simplifies the overall protection circuit structure.
4Measurement precision
If the selecting circuit switches between two sensing circuits based on output voltage, then the measurement precision is maintained across different voltage levels, but the device complexity increases due to the switching mechanism
Solution Approach 1:
The selecting circuit is designed with multi-functionality, serving not only to switch between sensing circuits but also to monitor voltage levels, detect protection conditions, and coordinate the operation of both sensing circuits. This universal approach allows a single circuit to perform multiple functions, maintaining measurement precision across all voltage levels while minimizing the complexity increase that would result from separate dedicated switching and monitoring circuits.
Data Source
AI summary
A power switch circuit is provided. The power switch circuit includes a power switch, a sensing circuit, a selecting circuit and a modulating circuit. The power switch has an output terminal for providing an output voltage and an output current. The sensing circuit is coupled to the power switch, senses the output current and outputs a current sensing signal. The selecting circuit is respectively coupled to the output terminal and the sensing circuit. The selecting circuit controls the sensing circuit according to the output voltage, so that the sensing circuit selectively outputs a first sensing current or a second sensing current as the current sensing signal. The modulating circuit is coupled to the sensing circuit and a control terminal of the power switch. The modulating circuit outputs a controlling voltage to the control terminal of the power switch, and modulates the controlling voltage according to the current sensing signal.