Buck Regulator Over-Current Protection with Foldback Control
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Solution Overview
Problem
Buck regulators face challenges in protecting against over-current conditions, leading to current limit runaway and undesirable inrush currents, especially at low output voltages, which can result in reliability issues and energy inefficiencies.
Innovation Solution
A controller-based system that selectively couples an inductor to a power supply, detects over-current events and low output voltages, and prevents current flow until all energy stored in the inductor is dissipated, employing a foldback mode to regulate inductor current and prevent runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional over-current protection is implemented in buck regulators, then current limiting is achieved, but current limit runaway and inrush currents occur at low output voltages
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors the output voltage of the buck regulator. When the output voltage drops below a threshold indicating a short-circuit condition, the system activates foldback current limiting. This feedback-based approach allows the regulator to distinguish between normal operation and fault conditions, preventing current limit runaway while maintaining protection functionality.
Solution Approach 2:
The patent employs dynamic current limiting where the current threshold is not fixed but adjusts based on output voltage conditions. During normal operation, standard current limiting applies. When low output voltage is detected (indicating short-circuit), the system transitions to foldback mode with reduced current thresholds. This dynamic adaptation prevents harmful inrush currents while maintaining effective over-current protection.
2Use of energy by moving object
If switching voltage regulator is used to convert battery voltage to lower DC voltage, then efficiency and size are improved, but switching currents cause noise problems
Solution Approach 1:
The patent extracts and separately manages the noise-related switching currents through dedicated current limiting circuits and foldback protection mechanisms. By isolating the noise-generating switching operations from the sensitive output stage through proactive current control, the system maintains high efficiency while reducing electromagnetic interference and noise propagation to connected devices.
3Reliability
If standard current limiting is applied in buck regulator, then over-current protection is provided, but energy dissipation is incomplete under short-circuit conditions
Solution Approach 1:
The patent applies preliminary detection of short-circuit conditions through output voltage monitoring before significant energy accumulation occurs in the inductor. By detecting low output voltage early and activating foldback current limiting proactively, the system prevents runaway conditions and ensures complete energy dissipation through controlled current reduction, avoiding both energy waste and potential damage.
Data Source
AI summary
Exemplary embodiments are related to a buck regulator. A buck regulator may include an inductor selectively coupled to an output and a power supply. The regulator may also include a controller configured to detect an over-current event if an amount of current flowing from the power supply to the inductor is equal to or greater than a current threshold and detect a low-voltage event if a voltage at the output is less than or equal to a reference voltage. Further, in response to the over-current event and the low-voltage event, the controller may be configured to prevent current from flowing from the power supply to the inductor until substantially all energy stored by the inductor has been dissipated.