Over-current Protection Circuit for Pulse Width Modulator
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Solution Overview
Problem
In pulse width modulators, the high-side switch can experience continuous current increase during the minimum on time due to parasitic inductance, leading to potential damage from overcurrent, as existing systems fail to adequately manage inductive current during this phase.
Innovation Solution
An over-current protection circuit is introduced, featuring a first pulse generator, counting unit, and overcurrent judging unit that temporarily stops the trigger's set signal output when an overcurrent is detected, allowing the inductive current to decrease, and resumes output after a predefined time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the high-side switch is turned on for minimum on time to ensure proper switching operation, then the switching reliability is improved, but the inductive current continuously increases during this period causing overcurrent damage
Solution Approach 1:
The patent applies preliminary action by detecting overcurrent conditions before the minimum on-time period ends and proactively extending the off-time accordingly. The control circuit monitors the inductive current during the minimum on-time period, and when overcurrent is detected, it extends the off-time to prevent the current from reaching damaging levels, thus acting in advance to avoid harm while maintaining reliable switching operation.
2Reliability
If the off-time is extended to decrease inductive current during overcurrent conditions, then the overcurrent protection is improved, but the switching frequency is reduced
Solution Approach 1:
The patent applies dynamics by making the off-time variable rather than fixed. The control circuit dynamically adjusts the off-time based on real-time detection of inductive current conditions. During normal operation, the off-time remains at the minimum required for reliable switching. During overcurrent conditions, the off-time is dynamically extended to decrease the inductive current, and this adjustment is temporary, allowing the system to return to normal switching frequency once the overcurrent condition is resolved.
3Measurement precision
If the inductive current is continuously monitored during minimum on time to detect overcurrent, then the overcurrent detection precision is improved, but the device complexity increases
Solution Approach 1:
The patent applies merging by integrating the overcurrent detection function into the existing control circuit that generates the minimum on-time signal. The same control circuit that generates the timing signal also monitors the inductive current and determines whether to extend the off-time. This consolidation avoids adding separate complex detection circuits while achieving precise overcurrent detection during the critical minimum on-time period.
Data Source
AI summary
An over-current protection circuit and a pulse width modulator having the same are provided. The pulse width module includes a high-side switch, a low-side switch, and a driving module. The driving module controls the high-side switch and the low-side switch according to a set signal and a reset signal periodically to adjust an inductive current flowing through the high-side switch and the low-side switch. When inductive current is the overcurrent during the minimum on time of the high-side switch, the over-current protection circuit turns off the high-side switch in a predefined time to decrease the inductive current continuously, so that the average current of the inductive current does not become too high to damage the pulse width module.