Bootstrapped Low-Side Switch for Negative Buck-Boost Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power converters in computer systems face inefficiencies when generating large negative voltages due to the use of level shifters, which consume significant power, and integrating a fly capacitor capable of storing the full negative voltage is difficult, especially in portable systems.
Innovation Solution
A power converter design that utilizes the parasitic gate-source capacitance of the low-side power FET to share charge with a fly capacitor, allowing bootstrapping without requiring the fly capacitor to be rated for the full negative voltage, thereby enabling efficient generation of negative voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fly capacitor is used to store the full negative voltage in a power converter, then the power conversion efficiency is improved, but the capacitor integration becomes difficult and the device complexity increases
Solution Approach 1:
The patent merges the fly capacitor function with the parasitic capacitance inherent in the low-side power FET. By utilizing the gate-source capacitance of the FET as part of the energy storage mechanism, the design eliminates the need for a separate high-voltage-rated fly capacitor, thereby reducing device complexity while maintaining power conversion efficiency.
Solution Approach 2:
The parasitic capacitance of the low-side power FET, which is normally a parasitic element, is repurposed to serve as part of the energy storage system. This self-service approach allows the FET's inherent capacitance to contribute to voltage generation, eliminating the need for additional dedicated components and simplifying the overall circuit design.
2Ease of operation
If a level shifter is used to generate gate voltage for the low-side power FET, then the power converter can operate, but significant power is consumed
Solution Approach 1:
The low-side power FET bootstraps itself by utilizing its own parasitic gate-source capacitance to generate the necessary gate voltage. This eliminates the need for an external level shifter circuit, thereby significantly reducing power consumption while maintaining the ability to operate the power converter.
Solution Approach 2:
The parasitic gate-source capacitance acts as an intermediary energy storage element that enables voltage boosting without requiring active level shifter circuitry. This intermediate capacitance allows the FET to achieve the necessary gate-drive voltage through passive charge transfer, reducing active power consumption.
3Temperature
If a fly capacitor with voltage rating equal to the negative voltage magnitude is used, then the full negative voltage can be generated, but the capacitor size increases and integration becomes difficult
Solution Approach 1:
The patent combines the fly capacitor functionality with the parasitic capacitance of the low-side power FET. This merging allows the system to achieve full negative voltage generation without requiring a large, high-voltage-rated discrete capacitor, thereby reducing the overall device complexity and improving integrability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for more efficient power conversion by using a smaller fly capacitor, reducing power consumption and enabling full integration, even if its voltage rating is less than the magnitude of the negative voltage generated.
Implementation Method 1
a capacitor, wherein a voltage rating of the capacitor is less than a magnitude of the negative voltage. The power converter also includes a control circuit configured to, during a first phase, cause the capacitor to accumulate a charge, and during a second phase, cause activation of the low-side switch by causing the capacitor to transfer a portion of the charge to a parasitic capacitance of the low-side switch
Implementation Method 2
cause activation of the low-side switch by causing the capacitor to transfer a portion of the charge to a parasitic capacitance of the low-side switch
Data Source
AI summary
A power converter with a bootstrapped switch is disclosed. A power converter is configured to generate a regulated supply voltage and includes an inductor coupled between a ground node and a switching node. The power converter further includes a switch (e.g., a low-side switch) coupled between the switching node and a supply voltage node, wherein the power converter is configured to generate the supply voltage on the voltage node, and a capacitor, wherein a voltage rating of the capacitor is less than a magnitude of the voltage. The power converter also includes a control circuit configured to, during a first phase, cause the capacitor to accumulate a charge, and during a second phase, cause activation of the switch by causing the capacitor to transfer a portion of the charge to a parasitic capacitance of the switch.