LDO Regulator Short-Circuit Protection Circuit
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Solution Overview
Problem
Conventional low drop out (LDO) regulator over-current protection circuits experience high power loss and thermal issues during short-circuit conditions, leading to increased risk of device failure due to clamping of output current at limited levels.
Innovation Solution
The proposed regulator over-current protection circuit switches off the pass device upon reaching a short-circuit current limit, reducing energy losses and thermal risks, and includes a mechanism to detect and automatically recover from short-circuit conditions without consuming direct current during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the output current is clamped at a short-circuit current limit in conventional LDO regulator circuits, then over-current protection is provided, but power loss and thermal generation become significantly high
Solution Approach 1:
The circuit dynamically switches between two protection modes: current clamping mode for moderate over-current conditions and shutdown mode for severe short-circuit conditions. The error amplifier and control logic adjust the pass transistor gate voltage dynamically based on the severity of the over-current condition, transitioning from maintaining regulated output to complete shutdown to minimize power loss while providing adequate protection.
Solution Approach 2:
The circuit changes the operating parameters of the pass transistor by adjusting its gate voltage based on feedback from the error amplifier. During normal operation, the transistor operates in linear region for regulation. During over-current conditions, the gate voltage is reduced to clamp current, and during severe short-circuits, it is reduced further to shut down the transistor completely, thereby changing power dissipation parameters from high to near-zero.
2Reliability
If the output current is clamped at a short-circuit current limit, then over-current protection is provided, but thermal-induced device failure risk increases
Solution Approach 1:
The circuit incorporates beforehand cushioning by designing the protection mechanism to progressively reduce power dissipation as over-current conditions worsen. The error amplifier and control logic prepare the circuit for thermal management by transitioning through intermediate states (current clamping) before reaching complete shutdown, cushioning against thermal buildup and preventing thermal-induced device failure.
3Loss of energy
If the pass device is switched off during short-circuit conditions, then power loss is reduced, but the circuit requires detection and recovery mechanisms
Solution Approach 1:
The circuit uses feedback through the error amplifier to continuously monitor the relationship between reference voltage and feedback voltage. This feedback mechanism automatically detects over-current conditions and triggers the appropriate protection response. During short-circuit, the feedback voltage drops, causing the error amplifier to reduce the pass transistor gate voltage, shutting it off. When the short-circuit is removed, feedback restoration automatically recovers normal operation without complex external control.
Solution Approach 2:
The protection circuit is self-service in that it automatically detects, responds to, and recovers from short-circuit conditions using its own internal components. The error amplifier and control logic form a self-contained system that requires no external intervention to detect the fault or initiate recovery, simplifying the overall system architecture while maintaining effective protection.
Data Source
AI summary
A signal source generates a reference voltage, and a voltage regulator receives the reference voltage and generates an output voltage and current. During normal operation, a pass element in the voltage regulator generates the output voltage, and a sense element generates a sense voltage. A first voltage detector detects a short-circuit condition using the sense voltage. A second voltage detector deactivates the pass element in response to the detection of the short-circuit condition. The second voltage detector also detects removal of the short-circuit condition and automatically reactivates the pass element. The first voltage detector may detect the short-circuit condition by detecting a drop in the sense voltage. The second voltage detector may detect the removal of the short-circuit condition by applying a test current to a load. Both the first and second voltage sensors may not consume any direct current power during normal operation of the voltage regulator.