Switching Power Supply Short Circuit Detection Offset Comparator
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Solution Overview
Problem
Existing switching power supplies face delays in detecting short circuits to ground, leading to prolonged operation of switching elements and potential damage, and have complex circuit structures for abnormality detection.
Innovation Solution
A switching power supply with a simple circuit structure incorporating a switching unit, error amplifier, soft-start circuit, PWM comparator, driving circuit, and offset comparator to quickly detect short circuits to ground by comparing soft-start and feedback voltages with an offset voltage, and a method for masking detection periods to manage short-circuit events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional short circuit protection methods are used, then the output transistor is protected from damage, but a delay time occurs between abnormality detection and load current stopping
Solution Approach 1:
The offset comparator is configured to detect short circuits to ground by comparing the soft-start voltage with the feedback voltage plus offset voltage before the mask period ends. This preliminary detection mechanism identifies abnormality earlier than conventional methods, triggering protection action before the predetermined mask period expires, thus reducing the delay time while maintaining transistor protection.
2Reliability
If conventional short circuit detection methods are used, then abnormality detection is performed, but the circuit structure becomes complicated
Solution Approach 1:
The offset comparator performs multiple functions: it compares the soft-start voltage with the feedback voltage plus offset voltage to detect short circuits to ground, and its output is integrated with the existing PWM control circuitry. This multi-functional approach enables short circuit detection without requiring separate dedicated detection circuits, thereby maintaining reliability while avoiding increased complexity.
Solution Approach 2:
The short circuit detection function is merged with the existing error amplifier and PWM comparator circuitry. The offset comparator's output is combined with the mask period control signal to generate the short circuit protection signal, integrating multiple functions into a unified control mechanism rather than using separate independent circuits.
3Productivity
If the switching element operates during the mask period after abnormality detection, then the load continues to receive power, but the output transistor is exposed to harmful current
Solution Approach 1:
The offset comparator continuously monitors the relationship between the soft-start voltage and the feedback voltage plus offset voltage during the mask period. When a short circuit to ground is detected (Vss ≥ Vfb + ΔV), the comparator immediately generates a short circuit protection signal that overrides the mask period control, providing real-time feedback to prevent overcurrent damage while the load would otherwise continue receiving power.
Data Source
AI summary
A switching power supply detects a short circuit to ground, for example, by comparing a soft-start voltage Vss with a feedback voltage Vfb while securing an offset voltage ΔV. The switching power supply includes, for example, a short-circuit-to-ground detection circuit which detects a short circuit to ground at a monitoring target terminal. When a short circuit to ground occurs for the first time, the output of the short-circuit-to-ground detection circuit is masked for a first period. When a short circuit to ground occurs for the second or any succeeding time, the output of the short-circuit-to-ground detection circuit is masked for a second period shorter than the first period.