Switched Capacitor Gate Drive With Reconfigurable Bulk Isolation
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Solution Overview
Problem
Switched capacitor converters face challenges in effectively controlling high-side switches due to the need for a gate voltage higher than the input power source voltage, leading to reverse conduction and inability to fully turn off the switches, which affects efficient charging and isolation in fast charging systems.
Innovation Solution
The implementation of a gate drive apparatus with a bulk switch and back-to-back connected diodes as an isolation switch, along with a bulk control circuit to manage the voltage potential, allowing for proper isolation and efficient switching by disconnecting the bulk terminal from the source during off-states, and using voltage clamping circuits to manage voltage stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-side switch is used to control power delivery in switched capacitor converter, then the switch can isolate the input power source from the output, but the gate voltage requirement exceeds the input power source voltage causing reverse conduction and inability to fully turn off the switch
Solution Approach 1:
A bootstrap capacitor is introduced as an intermediary energy storage element between the input power source and the high-side switch gate drive circuit. The bootstrap capacitor stores voltage during the low-side switch conduction phase and releases it to provide the necessary gate voltage elevation during the high-side switch conduction phase, enabling the gate voltage to exceed the input power source voltage without direct connection to the input source.
Solution Approach 2:
The bootstrap capacitor is charged in advance during the period when the low-side switch is conducting and the high-side switch is off. This preliminary charging action stores the necessary energy before it is needed, ensuring that when the high-side switch needs to turn on, the gate voltage is already prepared and can immediately exceed the input power source voltage level.
2Productivity
If the bulk terminal is connected to the source during switching operation, then the switch can conduct current efficiently, but reverse conduction occurs and the switch cannot be fully turned off
Solution Approach 1:
The bulk terminal connection is made dynamic rather than static. During the on-state, the bulk terminal is connected to the source through a bulk switch to enable efficient current conduction. During the off-state, the bulk switch opens to disconnect the bulk terminal from the source, preventing reverse conduction through the body diode and enabling complete switch turn-off. This dynamic reconfiguration resolves the contradiction between conduction efficiency and turn-off capability.
Data Source
AI summary
A power converter includes a plurality of power switches connected in series between a system ground and an input voltage bus, wherein an upper power switch located between the input voltage bus and an output terminal of the power converter, and immediately adjacent to the output terminal of the power converter is configured as an isolation switch including two back-to-back connected diodes and a bulk terminal, and wherein a connection of the bulk terminal is reconfigurable, and a driver configured to drive the upper power switch immediately adjacent to the output terminal of the power converter.