Soft-Charging Switched Capacitor Converter Bypass Circuit
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Solution Overview
Problem
Switched capacitor DC-DC converters face high in-rush currents during power up or fast input voltage transients, which can shorten the life of switching transistors and cause damage, and existing solutions either incur significant power loss, size, cost, and complexity or have long pre-charge times.
Innovation Solution
A switched capacitor power converter with an auxiliary soft-charge bypass circuit that includes auxiliary transistors and an impedance element, allowing for an auxiliary circuit path to charge capacitors when the main switching transistors are deactivated, reducing stress on the main transistors and capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dedicated current sources are inserted to provide pre-charging currents, then in-rush current is reduced, but pre-charge time becomes long and load current delivery is insufficient
Solution Approach 1:
The patent uses dynamic control of the auxiliary transistor switching during soft-charging mode to adaptively manage the charging current. The auxiliary transistor is periodically switched on and off to charge the capacitor while limiting in-rush current, and this dynamic switching allows the system to transition from soft-charging mode to normal switching mode when charging is complete, thus reducing pre-charge time while protecting the transistor.
Solution Approach 2:
The auxiliary transistor is controlled to switch periodically during soft-charging mode, creating periodic charging pulses that gradually charge the capacitor. This periodic action allows controlled energy transfer without excessive current spikes, and the periodic switching also enables the system to detect when charging is complete, thereby reducing overall pre-charge time.
2Reliability
If hot-swap input converter is added to convert step increases, then in-rush current is limited, but conduction loss increases and board real estate is occupied
Solution Approach 1:
The auxiliary soft-charge bypass circuit is pre-configured in parallel with the main switching transistor before power-up or transient events occur. When a voltage step is detected, the auxiliary circuit is immediately activated to provide a controlled charging path, limiting in-rush current before it can damage the main transistor. This preliminary preparation eliminates the need for additional hot-swap converters, reducing both conduction loss and board space.
Solution Approach 2:
The auxiliary transistor and impedance element form an intermediary circuit path that mediates between the voltage source and the main switching transistor during transient events. This intermediary path provides controlled current flow, protecting the main transistor from in-rush currents without requiring the main transistor to handle full power during transients, thereby reducing conduction loss and eliminating the need for large hot-swap input converters.
3Reliability
If auxiliary soft-charge bypass circuit is used, then in-rush current is limited without significant power loss, but device complexity increases
Solution Approach 1:
The auxiliary soft-charge bypass circuit is designed to perform multiple functions: it provides in-rush current limiting during power-up, protects against fast input voltage transients, and enables controlled soft-charging of capacitors. By integrating these functions into a single auxiliary circuit that shares components with the main switching path, the patent reduces overall device complexity compared to having separate circuits for each function.
Solution Approach 2:
The auxiliary soft-charge bypass circuit is merged with the main switching transistor path, sharing common components such as the impedance element and control circuitry. The auxiliary transistor is integrated into the existing switching architecture, and the control circuit uses the same voltage detection and timing mechanisms already present in the converter. This merging approach limits in-rush current while minimizing the increase in device complexity.
Data Source
AI summary
A switched capacitor power converter includes multiple switching transistors in a default switching path, and an auxiliary soft-charge bypass circuit which includes one or more auxiliary transistors and an impedance element, and provides an auxiliary circuit path through the auxiliary transistor(s) to charge a plurality of capacitors within the converter circuit when the auxiliary soft-charge bypass circuit is activated and at least one of the switching transistors is deactivated. A corresponding control circuit switches the converter circuit from a soft-charging mode in which the auxiliary soft-charge bypass circuit is activated and a switching transistor is deactivated, to an operational mode in which the auxiliary soft-charge bypass circuit is deactivated, the control circuit periodically switching the one or more auxiliary transistors during the soft-charging mode in place of the deactivated switching transistor(s).