Switching Power Supply Overcurrent Protection via Pulse Skipping
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Solution Overview
Problem
Conventional pulse-by-pulse overcurrent protection circuits in switching power supply devices often result in delayed limiting of inductor current, leading to potential breakdown due to repeated forcible-stop and self-return switching operations, especially during extreme overcurrent conditions.
Innovation Solution
The introduction of a pulse skip circuit that includes a frequency dividing part, RS flipflop, timer part, and logic gates to generate a mask signal that blocks the clock signal during overcurrent events, thereby skipping pulses and extending the mask period as output voltage decreases, effectively enhancing overcurrent protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulse-by-pulse overcurrent protection is implemented with repeated forcible-stop and self-return switching operations, then the switching operation can be restored after temporary overcurrent, but the inductor current limiting is delayed causing potential circuit breakdown
Solution Approach 1:
The mask circuit generates a mask signal in advance when overcurrent is detected, before the switching operation completes its natural cycle. This preliminary action prevents the delayed self-return that causes inductor current to continue rising, thereby resolving the contradiction between maintaining protection function and eliminating current limiting delay
Solution Approach 2:
The invention skips the delayed self-return phase by introducing a mask signal that forcibly prevents the switching operation from resuming during the dangerous period. This allows the system to rush through the critical overcurrent condition without waiting for the natural pulse cycle to complete, eliminating the time loss while maintaining protection
2Reliability
If the switching operation is forcibly stopped to limit overcurrent, then circuit breakdown is prevented, but the output voltage drops and power efficiency decreases
Solution Approach 1:
Instead of completely stopping the switching operation, the mask circuit applies partial action by selectively masking only the critical pulses during overcurrent conditions. This allows the switching operation to continue at reduced capacity rather than fully stopping, thereby maintaining some power transfer while still providing protection, resolving the contradiction between circuit protection and power efficiency
Solution Approach 2:
The mask signal is applied periodically only when overcurrent conditions are detected, rather than continuously blocking all switching operations. This periodic intervention allows normal operation to proceed efficiently most of the time, while providing protection only when needed, thus resolving the contradiction between continuous protection and power efficiency
Data Source
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AI summary
A switching power supply device (100) includes: a switching output circuit (110) configured to generate an output voltage from an input voltage; an oscillation circuit (150) configured to generate a clock signal; a control circuit (180) configured to control driving of the switching output circuit (110) in synchronization with the clock signal; a pulse-by-pulse type overcurrent protection circuit (X) configured to detect an overcurrent flowing through the switching output circuit (110) to generate an overcurrent protection signal for forcibly stopping a switching operation of the switching output circuit (110); and a pulse skip circuit (Y) configured to perform a pulse skip operation of the clock signal in response to the overcurrent protection signal.