Soft-Start Control for Switched-Capacitor Converters
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Solution Overview
Problem
Switched-capacitor converters (SCCs) face high inrush currents during start-up, causing electrical stress and triggering overcurrent protection, which existing solutions address at the cost of additional circuitry and reduced efficiency.
Innovation Solution
A soft-start circuit limits current by generating a ramped voltage applied to the first switch, controlling the voltage at its second terminal, thus reducing initial current without requiring additional power switches or complex pre-charging circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current-limiting circuit with a shunt resistor and power switch is added to limit inrush current, then the inrush current problem is addressed, but the device complexity increases and efficiency decreases due to additional power loss
Solution Approach 1:
The invention extracts the current limiting function from a separate dedicated circuit and integrates it into the existing first power switch of the SCC. By utilizing the gate control terminal of the existing switch, the patent eliminates the need for additional current-limiting circuitry while maintaining effective inrush current protection.
Solution Approach 2:
The first power switch in the SCC is made multi-functional by using its gate control terminal to perform both the primary switching function and the current limiting function. This universal approach allows a single component to handle multiple tasks, reducing overall circuit complexity while maintaining reliability.
2Reliability
If pre-charging circuitry is added to charge capacitors during start-up, then inrush current is limited, but the device complexity and control complexity increase significantly
Solution Approach 1:
The invention removes the need for separate pre-charging circuitry by integrating the current limiting capability into the existing first power switch. This extraction of the pre-charging function into the main switch eliminates additional circuitry and simplifies the overall system.
Solution Approach 2:
The first power switch serves itself by using its own gate control terminal to regulate the current during start-up. This self-service approach eliminates the need for external pre-charging circuits and complex control sequences, as the existing switch infrastructure handles the current limiting autonomously.
3Reliability
If additional power switches are added to limit current, then inrush current is controlled, but the efficiency of the SCC decreases during steady-state operation
Solution Approach 1:
The invention extracts the current limiting function from a separate power switch and assigns it to the existing first power switch. This eliminates the need for additional power switches that would cause power loss during steady-state operation, as the same switch handles both start-up current limiting and normal operation.
Solution Approach 2:
The first power switch is made universal to perform both current limiting during start-up and normal power switching during steady-state operation. This multi-functionality ensures that no additional power switches are required, thereby maintaining high efficiency during steady-state operation while still providing inrush current protection.
Data Source
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AI summary
Circuits and methods are provided for soft-starting a switched-capacitor converter (SCC), so as to limit inrush current at the start-up of the SCC. This is accomplished by using the first power switch of the SCC, i.e., the switch coupled to the input of the SCC, to reduce the voltage provided at the SCC input, such that the full input voltage is not directly applied to the SCC circuitry downstream from the first power switch during the SCC start-up. The reduced voltage provided to the SCC circuitry (other than the first power switch) serves to limit the current drawn by the remainder of the SCC circuit during the SCC start-up. This reduced voltage begins at zero and ramps to the voltage provided at the SCC input. Once the reduced voltage reaches the input voltage level, steady-state operation of the SCC may begin.