On-Chip Soft-Start Circuit for DC/DC Converter
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Solution Overview
Problem
Conventional soft-start circuits for switching mode DC/DC converters experience inrush current and overshoot voltage issues during startup, leading to potential system damage and reduced efficiency, especially when duty ratio is low and switching frequency is slow or high.
Innovation Solution
Adaptive adjustment of switching frequency during the soft-start period by multiplying the rated switching frequency by a second predetermined value when the detected output voltage is below a certain threshold, and reverting to the rated frequency when the output voltage exceeds this threshold, using an on-chip soft-start circuit method.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the switching frequency is reduced to slow down the startup process, then the overshoot voltage is reduced, but the inrush current increases and the startup time extends
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable rather than fixed. The controller dynamically changes the switching frequency based on the detected output voltage level: using a first switching frequency when the output voltage is below a reference value, and switching to a second switching frequency when the output voltage exceeds the reference value. This dynamic adjustment resolves the contradiction by adapting the frequency to the real-time state of the converter.
Solution Approach 2:
The patent changes the switching frequency parameter according to the output voltage condition. By detecting whether the output voltage is below or above a reference value, the controller selects appropriate frequency values to optimize performance. This parameter change strategy allows the system to avoid both excessive inrush current and overshoot voltage by using different frequency settings for different operating phases.
2Loss of time
If the switching frequency is increased to speed up the startup process, then the startup time is reduced, but the inrush current and overshoot voltage increase beyond safe ranges
Solution Approach 1:
The patent applies preliminary action by first using a lower switching frequency during the initial startup phase when the output voltage is below the reference value. This preliminary low-frequency operation allows the output voltage to rise smoothly without generating excessive inrush current or overshoot voltage. Once the output voltage exceeds the reference value, the controller then switches to a higher frequency to complete the startup process quickly, thus achieving both safe startup and fast response.
Solution Approach 2:
The patent uses periodic action by dividing the startup process into two distinct phases based on the output voltage level. The controller periodically monitors the output voltage and switches between two frequency modes: a first frequency mode for the initial voltage buildup phase and a second frequency mode for the final voltage regulation phase. This periodic switching resolves the contradiction between fast startup and safe operation.
3Device complexity
If a conventional soft-start circuit is used, then the circuit structure is simple, but it cannot effectively control inrush current and overshoot voltage under varying duty ratios and switching frequencies
Solution Approach 1:
The patent applies feedback by using a detector to monitor the output voltage and provide this information to the controller. Based on the feedback signal indicating whether the output voltage is below or above the reference value, the controller automatically adjusts the switching frequency. This feedback mechanism enables the simple circuit structure to achieve effective control of inrush current and overshoot voltage under varying operating conditions.
Data Source
AI summary
Methods of a switching mode DC/DC converter are provided in the present invention. The proposed method includes a step of causing a switching frequency of the converter to be operated at a rated value multiplied by a second predetermined value when an output voltage of the converter is not larger than a first predetermined value.