Switching Regulator Negative Current Limiting With Timed Tri-State Recovery
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Solution Overview
Problem
Conventional switching regulators face challenges in safely managing negative current operations, which can lead to damage to power switches due to prolonged high-side power switch activation and potential negative current runaway.
Innovation Solution
A negative current protection circuit is implemented in the switching regulator, which limits negative current to a threshold by turning off the low-side power switch and turning on the high-side power switch for a maximum time period. If the negative current has not recovered, the circuit enters a tri-state mode where both power switches are turned off, preventing damage and runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the high-side power switch is turned on to limit negative current, then negative current is limited to threshold, but the high-side power switch may remain on too long causing damage
Solution Approach 1:
The patent applies preliminary action by setting a predetermined maximum on-time for the high-side power switch before actual damage can occur. The controller monitors the on-time duration and automatically turns off the high-side power switch when the maximum on-time is reached, preventing potential damage from prolonged conduction while maintaining effective negative current limiting during normal operation.
2Reliability
If both power switches are turned off to prevent damage, then negative current runaway is prevented, but the regulator enters tri-state mode reducing productivity
Solution Approach 1:
The patent applies periodic action by implementing a systematic tri-state mode operation where both power switches are turned off at specific intervals when negative current exceeds the threshold. This periodic interruption prevents continuous negative current runaway while allowing the regulator to resume normal operation once the condition is resolved, balancing protection with operational continuity.
3Reliability
If the low-side power switch is turned off to limit negative current, then negative current is controlled, but the circuit complexity increases
Solution Approach 1:
The patent applies merging by combining the control of both power switches under a unified negative current protection mechanism. The controller integrates the threshold detection, maximum on-time monitoring, and tri-state mode activation into a single coordinated control logic, managing the complexity of controlling both switches through one centralized protection scheme rather than separate independent controls.
Data Source
AI summary
A controller for a switching regulator incorporates a protection circuit to limit the negative current to a negative current threshold while operating the switching regulator to sink current from the load without damage to the power switches. In some embodiments, in response to the negative current reaching the negative current threshold, the protection circuit turns off the low-side power switch and turns on the high-side power switch for a maximum time period. In the event the negative current has not recovered, the high-side power switch and the low-side power switch are both turned off while the high-side power switch conducts the negative current through the high-side power switch body diode. When the negative current recovers to a recovery level, the low-side power switch can then be turned on. The protection circuit repeats the process each time the negative current is detected to have reached the negative current threshold.