SMPS Control Circuit for Peak Current Buildup Prevention
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Solution Overview
Problem
Existing switched-mode power supply (SMPS) systems face issues with peak current value accumulation during start-up or output short circuit conditions, leading to potential component damage and inefficient operation due to the need for increased saturation currents and improper frequency adjustments.
Innovation Solution
The SMPS is controlled to switch between different operating modes based on output voltage levels, using a control method that adjusts the operating frequency and on-time to maintain a proportional relationship, operate at a fixed frequency, or vary frequency to prevent peak current accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the operating frequency is lowered to prevent peak current accumulation, then the peak current value is controlled, but the system requires larger components with greater saturation current capability leading to increased size and cost
Solution Approach 1:
The patent applies dynamics by making the minimum on-time dynamic rather than fixed. The minimum on-time is adjusted based on the output voltage level: during start-up or short-circuit conditions when output voltage is low, a longer minimum on-time is enforced to ensure adequate energy transfer and prevent peak current accumulation, while under normal operating conditions the minimum on-time is relaxed to allow higher switching frequencies and smaller component sizes. This dynamic adjustment resolves the contradiction between current control and component size.
2Productivity
If the system operates at maximum frequency to improve efficiency, then the switching speed increases, but the inductor current cannot demagnetize fully leading to current accumulation
Solution Approach 1:
The patent applies dynamics by making the on-time adaptive rather than fixed at maximum frequency. During normal operation, the system operates at high switching frequency with a relaxed minimum on-time for efficiency. However, during start-up or short-circuit conditions, the minimum on-time is extended to ensure adequate demagnetization time, allowing the inductor current to fully reset before the next switching cycle. This dynamic adjustment resolves the contradiction between switching frequency and current demagnetization.
Data Source
AI summary
A control method and control circuit for a switched-mode power supply (SMPS) and a control chip are disclosed. The SMPS is switched between different operating modes based on different levels of its output voltage. When the output voltage is lower than a first reference and the difference between it and the first reference exceeds a threshold, an operating frequency of a power transistor and output voltage are controlled to satisfy a proportional relationship defined by an associated slope. When the output voltage is lower than the first reference and the difference between it and the first reference is below the threshold, the power transistor is controlled to operate at a fixed frequency. When the output voltage is higher than the first reference, the power transistor is controlled to operate at a variable frequency.