SMPS Control Circuit Soft-Start Limiting for Overshoot Suppression
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Solution Overview
Problem
Existing switched-mode power supplies experience output voltage and inductor current overshoots during startup due to the lack of offset voltage calibration in soft-start designs, leading to abnormal operation or damage.
Innovation Solution
A control circuit for switched-mode power supplies that includes an error amplifier module, a soft-start voltage generation module, an amplitude limiter module, and a PWM comparator module, which limits the amplitude of the error amplifier signal based on the soft-start reference voltage to prevent overshoots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft-start function is incorporated to limit output voltage/current/power during startup, then system safety is improved, but output voltage and inductor current overshoots occur due to EA signal deviation
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the offset voltage of the error amplifier before the soft-start process begins. The offset calibration circuit determines and stores the appropriate offset voltage value in advance, ensuring that when soft-start is activated, the EA signal remains accurate and does not deviate or saturate, thereby preventing overshoots while maintaining safety limitations.
Solution Approach 2:
The patent introduces an intermediary offset calibration circuit that mediates between the error amplifier and the soft-start function. This intermediary component pre-determines the correct offset voltage and provides it to the EA, enabling the EA signal to accurately reflect the difference between feedback and reference voltages without deviation, thus preventing harmful overshoots while the soft-start limiter protects the system.
2Manufacturing precision
If negative feedback loop is established at startup for accurate output voltage control, then manufacturing precision is improved, but EA output signal deviates from equilibrium value causing output ripple
Solution Approach 1:
The patent applies preliminary action by performing offset voltage calibration before the negative feedback loop becomes active. The offset calibration circuit pre-determines and stores the correct offset voltage value, ensuring that when the feedback loop starts operating, the EA output signal is already properly calibrated and remains stable at the equilibrium value, preventing output ripple while maintaining accurate voltage control.
Solution Approach 2:
The patent uses feedback by implementing an offset calibration circuit that monitors the EA output signal and adjusts the offset voltage to maintain the signal at its equilibrium value. This feedback mechanism ensures that the EA output remains stable and does not deviate, allowing the negative feedback loop to operate accurately from startup without causing output ripple.
Data Source
AI summary
A switched-mode power supply and a control circuit for use in a switched-mode power supply are disclosed. In addition to an EA module, a PWM comparator module and a soft-start voltage generation module, the control circuit also includes an amplitude limiter module for limiting the amplitude of an EA signal based on a soft-start reference voltage and thereby enabling the amplitude of a signal input to the PWM comparator module from the EA module to follow a soft-start control signal and vary stably and smoothly. This can reduce the risk of output voltage and inductor current overshoots due to DC loop establishment during startup of the switched-mode power supply, enhance stability and safety of the power supply system during startup, and accelerate the DC loop establishment.