Switched-Mode Power Supply Overcurrent Protection Using Adjusting Signal
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Solution Overview
Problem
In switched-mode power supplies, there is a signal delay issue that causes the inductor current to exceed the peak limit, leading to undesirable variations in output voltage with input voltage changes, as the switch is not turned off promptly enough.
Innovation Solution
A control method that generates a summation signal by adding a current-sense signal to an adjusting signal and compares it with a peak limit, turning off the switch when the summation exceeds the limit, and updates the adjusting signal based on the switch's turn-on time or duty cycle to maintain constant current limits, using a controller with a logic processing unit, comparator, and current generator to adjust the adjusting current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a comparator is used to detect when the current-sense signal exceeds the peak limit, then over current protection is achieved, but signal delay causes the current to exceed the limit by an amount that varies with input voltage
Solution Approach 1:
The patent applies preliminary action by adding the adjusting signal to the current-sense signal before comparison. This advance adjustment compensates for the upcoming signal delay, ensuring that when the comparator triggers, the switch turns off at the correct moment. The adjusting signal is calculated based on expected delay characteristics, allowing the system to pre-compensate for the delay rather than react to it.
Solution Approach 2:
The patent implements feedback by using the turn-on time or duty cycle information to dynamically update the adjusting signal. The controller monitors the actual switch operation and adjusts the adjusting signal accordingly, creating a closed-loop system that continuously optimizes the current limit accuracy despite variations in input voltage and signal delay.
2Device complexity
If the switch is turned off based on a fixed peak limit comparison, then the control logic is simple, but the maximum output power varies with input voltage due to signal delay
Solution Approach 1:
The control logic remains relatively simple while applying preliminary action through the adjusting signal addition. The comparator still performs a straightforward comparison, but the comparison is now between the summation signal (current-sense + adjusting) and the peak limit. This preliminary adjustment maintains operational simplicity while achieving accurate current limiting that stabilizes output power across varying input conditions.
Solution Approach 2:
The patent applies parameter changes by dynamically modifying the adjusting signal based on turn-on time or duty cycle. Instead of changing the peak limit itself, the system adjusts the effective threshold through the adjusting signal parameter, allowing the current limit to adapt to varying operating conditions while maintaining a simple fixed peak limit comparator structure.
3Speed
If no adjustment is made for signal delay, then the system is fast and responsive, but the inductor current exceeds the peak limit leading to unstable output voltage
Solution Approach 1:
The system maintains fast response by applying preliminary action rather than waiting for delay compensation. The adjusting signal is added in advance based on predicted delay characteristics, allowing the comparator to trigger at the correct moment without adding noticeable delay to the overall response. This pre-compensation approach preserves speed while achieving stability.
Solution Approach 2:
The patent applies preliminary anti-action by anticipating the harmful effect of signal delay and counteracting it in advance. The adjusting signal is designed to offset the expected current increase during the delay period, preventing the current from exceeding the limit rather than correcting it after the fact. This proactive approach maintains both speed and stability.
Data Source
AI summary
Control methods and controller thereof for a power supply including a power switch and an inductor. The power switch is turned on to increase the inductor current through the inductor, which is sensed to generate a current-sense signal. The current-sense signal is added up with an adjusting signal to generate a summation signal. The power switch is turned off if the summation signal is higher than a peak limit. The turn-on time of the power switch is detected to update the adjusting signal.