Capacitor Voltage Initialization in Switch-Capacitor Regulators
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Solution Overview
Problem
Switch-capacitor regulators face challenges in initializing the voltage across capacitors accurately, leading to potential damage from inrush current when charging the capacitor at startup, especially in designs requiring low-voltage components.
Innovation Solution
A startup circuit comprising a voltage forming circuit and a control unit that operates in three phases to set and maintain the voltage across the capacitor's top and bottom to a preset initial voltage, using switches, a current mirror circuit, and a comparator to manage the charging process, preventing large current flow and ensuring accurate voltage initialization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large current is supplied to charge the capacitor at the initial stage to achieve accurate initial voltage, then the initial voltage accuracy is improved, but inrush current damages the chip
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor through a dedicated startup circuit before the main power switch is activated. The startup circuit charges the capacitor to a predetermined initial voltage (e.g., half of input voltage for three-level buck converters) before normal operation begins, avoiding the need for large inrush current during startup.
Solution Approach 2:
The patent segments the charging function by separating the startup charging path from the normal operation path. A dedicated startup circuit with its own charging path is provided, independent from the main power conversion circuit. This segmentation allows the capacitor to be charged to the required initial voltage without affecting the main circuit and without causing inrush current to the main power switch.
2Power
If low-voltage components are used to reduce on-resistance of the circuit, then the on-resistance is reduced, but the initial voltage must be accurate to prevent damage to low-voltage components
Solution Approach 1:
The startup circuit performs preliminary action by establishing the correct initial voltage across the capacitor before the low-voltage components are activated. By pre-charging the capacitor to the exact required voltage level, the system ensures that when low-voltage components start operating, they receive precisely the voltage they need, preventing damage while maintaining low on-resistance.
3Device complexity
If the switch-capacitor regulator starts operation without proper initial voltage initialization, then the startup process is simplified, but the voltage across the capacitor may be inaccurate causing component damage
Solution Approach 1:
The patent segments the startup function into a separate dedicated circuit module. The startup circuit is an independent segment that handles only the capacitor initialization task, while the main power conversion circuit handles normal operation. This segmentation adds minimal complexity to the overall system while ensuring reliable component protection through accurate initial voltage establishment.
Data Source
AI summary
A startup circuit initializes a voltage of a capacitor of a switch-capacitor regulator. The startup circuit includes a voltage forming circuit and a control unit. The voltage forming circuit selectively electrically connected to the top and the bottom of the capacitor. In a first operation phase, the voltage forming circuit is electrically connected to the top and bottom of the capacitor, and the top and bottom of the capacitor are connected to each other, and the voltages of the top and bottom are set as a preset high voltage. In a second operation phase, the voltage forming circuit disconnects the top and the bottom, and generates current flowing out from the bottom of the capacitor until the voltage cross the capacitor is equal to the preset initial voltage. In the third operation phase, the startup circuit is disconnected from the capacitor.