Self-Bootstrap Driving Circuit for DC-DC Converters
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Solution Overview
Problem
The decreasing minimum voltage level in automotive systems poses challenges for generating sufficient Gate-Source voltage (Vgs) overdrive for high-side MOSFETs in Buck and Buck-Boost DC-DC converters, leading to increased conduction losses and reduced power efficiency, particularly in Buck topology at low Vsup values.
Innovation Solution
A self-bootstrap driving circuit that utilizes the over-voltage generated by an inductor to directly transfer charges to the gate of the high-side MOSFET, eliminating the need for external capacitors and charge pump structures, thereby ensuring a sufficient gate overdrive independent of the Vsup voltage level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the Vsup voltage level is reduced to meet automotive requirements, then the power supply voltage adapts to automotive standards, but the Gate-Source voltage overdrive for the HS MOSFET becomes insufficient
Solution Approach 1:
The patent introduces a bootstrap capacitor (Cboot) and associated circuitry as an intermediary energy storage mechanism. This capacitor stores energy during the low-side switch conduction phase and releases it during the high-side switch conduction phase, providing the necessary voltage boost to the gate driver independent of the declining Vsup level. The intermediary capacitor decouples the gate drive voltage from the supply voltage, resolving the contradiction between adapting to lower automotive voltages and maintaining sufficient gate overdrive.
2Reliability
If conventional charge pump structures are used to provide sufficient gate overdrive, then the Gate-Source voltage is adequate, but the device complexity and cost increase due to additional pins and external capacitors
Solution Approach 1:
The patent merges the bootstrap capacitor function with the existing low-side switch body diode and inductor, creating an integrated energy recovery path. Instead of requiring separate charge pump components, the circuit utilizes the existing power conversion elements to charge the bootstrap capacitor during the low-side conduction period. This merging approach provides sufficient gate overdrive while minimizing additional components and complexity.
Solution Approach 2:
The bootstrap circuit is self-charging through the body diode of the low-side MOSFET and the inductor current. During the low-side switch conduction phase, the inductor current flows through the body diode, automatically charging the bootstrap capacitor without requiring external power sources or complex control circuitry. This self-service mechanism eliminates the need for additional pins and external capacitors that would be required in conventional charge pump structures.
3Reliability
If the HS MOSFET is over-sized to compensate for insufficient gate overdrive, then the Gate-Source voltage becomes adequate, but the conduction losses increase and power efficiency deteriorates
Solution Approach 1:
The bootstrap capacitor acts as an intermediary that provides the necessary gate drive voltage without requiring an oversized MOSFET. By storing and releasing energy at the appropriate times, the capacitor ensures adequate gate overdrive voltage is applied to the MOSFET gate, allowing the device to operate with optimal sizing rather than requiring excessive device dimensions that would increase conduction losses.
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 solution reduces conduction losses, increases overall system efficiency, and simplifies the design by eliminating the need for expensive charge storage and transfer capacitors, while maintaining a 100% duty cycle for the high-side switch without additional components.
Implementation Method 1
utilizes the over-voltage generated by an inductor to directly transfer charges to the gate of the high-side MOSFET
Implementation Method 2
a current path between said output and said control terminal arranged to provide direct transfer from an output of said electro-inductive component to said control terminal of over-voltage generated at said output
Data Source
AI summary
A self-bootstrap driving circuit includes a first input receiving a first control signal; an output, to which a load having an electro-inductive component may be connected; a power switch having first and second current terminals and a control terminal, and being arranged to drive power from a power supply terminal to the load; a bootstrap circuitry arranged to drive the control terminal of the power switch based on the control signal; and a current path between the electro-inductive component of the load and the control terminal of the switch, said current path being arranged to provide direct transfer from said electro-inductive component to said control terminal of the switch of an overvoltage generated at the electro-inductive component to provide an overdrive voltage to said control terminal of the switch.