Soft-Start Voltage Circuit Using Segmented Capacitor Switching
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Solution Overview
Problem
Conventional soft-start voltage circuits for DC/DC converters require large capacitors or small current sources to achieve a gradual rise in soft-start voltage, leading to area wastage and fabrication issues, making it inconvenient to control the soft-start phase effectively.
Innovation Solution
A soft-start voltage circuit comprising an operational amplifier, a voltage level shifter, two capacitors, and switches, where the clock signal and offset voltage control the slope of the soft-start voltage, allowing for precise control of the soft-start phase without the need for large capacitors or small current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a capacitor with large capacitance is used to achieve a gradual rise in soft-start voltage, then the soft-start phase is prolonged, but the chip area occupied is large
Solution Approach 1:
The patent divides the soft-start voltage generation into two distinct phases: a first soft-start phase using a first capacitor and second capacitor in series, and a second soft-start phase using the first capacitor alone. This segmentation allows the circuit to achieve prolonged soft-start duration without requiring a single large capacitor, thereby reducing chip area occupation while maintaining the desired gradual voltage rise characteristics.
2Duration of action of moving object
If a current source with small magnitude is used to achieve a gradual rise in soft-start voltage, then the soft-start phase is prolonged, but the current source is easily affected by fabrication variations
Solution Approach 1:
The patent employs dynamic switching between different capacitor configurations (series connection in first phase, parallel connection in second phase) to control the soft-start voltage rise. This dynamic approach replaces the static small current source with a switching mechanism that is less sensitive to fabrication variations, achieving prolonged soft-start phase while improving manufacturing precision and current source stability.
Solution Approach 2:
The patent implements periodic switching between different capacitor arrangements through control signals. The first switch connects capacitors in series during the first phase, then switches to parallel connection during the second phase. This periodic action creates a controlled gradual voltage rise without relying on a small, fabrication-sensitive current source, thereby extending soft-start duration while reducing sensitivity to manufacturing variations.
3Object-generated harmful factors
If the soft-start voltage rises gradually to prolong the soft-start phase, then the inrush current is reduced, but the control convenience is decreased
Solution Approach 1:
The patent incorporates control circuits that monitor the soft-start voltage level and automatically switch between different capacitor configurations based on voltage thresholds. This feedback mechanism maintains gradual voltage rise to reduce inrush current while automating the control process, thereby preserving the benefit of reduced inrush current while improving control convenience through automatic switching rather than manual adjustment.
Data Source
AI summary
A soft-start voltage circuit includes an operational amplifier, a first and a second capacitors, a first and a second switches, and a voltage level shifter. The operational amplifier includes a positive end, a negative end, and an output end coupled to the negative end of the operational amplifier for outputting the soft-start voltage. The voltage level shifter is coupled between the first capacitor and the positive end of the operational amplifier for shifting a level of the voltage on the first capacitor. The first switch is coupled between the first and the second capacitors for coupling the first and the second capacitors according to the clock. The second switch is coupled between the second capacitor and the negative end of the operational amplifier for coupling the second capacitor and the negative end of the operational amplifier according to the inverted clock.