Bootstrap FET Power Switching With Reverse Current Blocking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing power supply systems face inefficiencies and increased size, weight, and cost due to the use of charge pumps, isolated power supplies, and drive transformers for switching power supplies, which also fail to provide fast switching speeds and efficient reverse current blocking.
Innovation Solution
A power supply control system utilizing a pair of back-to-back FETs with a bootstrap capacitor charged by a non-isolated power supply to generate the gate-to-source voltage for switching, allowing shared use across multiple circuits, reducing the need for multiple large components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If charge pumps, isolated power supplies, and drive transformers are used to switch high-side FETs, then the power supply can be switched, but the system size, weight, and power consumption increase significantly
Solution Approach 1:
The patent combines the gate drive function and power supply switching function into a single bootstrap capacitor circuit. The bootstrap capacitor serves dual purposes: it provides the gate-to-source voltage needed to turn on the FET and simultaneously acts as the power supply switching mechanism. This eliminates the need for separate charge pumps, isolated power supplies, and drive transformers, thereby reducing system weight while maintaining reliable power supply switching capability.
2Ease of operation
If diodes are used for reverse current blocking, then current direction can be controlled, but power loss increases due to diode voltage drop
Solution Approach 1:
The patent replaces the mechanical diode-based reverse current blocking mechanism with an electronic FET-based solution. The FETs, when properly controlled through the bootstrap capacitor, provide bidirectional current blocking capability without the inherent voltage drop of diodes. This substitution maintains ease of operation for current direction control while significantly reducing power loss associated with diode voltage drops.
3Ease of operation
If large charge pumps and isolated power supplies are used, then high-side FETs can be switched, but device complexity and cost increase
Solution Approach 1:
The patent extracts the essential function needed for high-side FET switching - the gate-to-source voltage generation - and implements it using a simple bootstrap capacitor circuit. By taking out only the necessary function rather than using complex charge pumps and isolated power supplies, the patent achieves high-side FET switching capability with minimal circuit complexity and lower cost.
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
The system achieves efficient and fast switching of power supplies, minimizing power loss and system size while maintaining reliability and reducing costs.
Implementation Method 1
a first bootstrap capacitor, which may be configured to be pre-charged to a second power supply voltage when the first compound switch is in an 'off' state, and configured to provide the second power supply voltage as the 'on' gate-to-source voltage level to the first voltage driving circuitry when the first compound switch is to be placed in the 'on' state
Data Source
AI summary
In an example a power supply control system for switchably routing at least a first power supply voltage to an output voltage supply node may include a first compound switch circuit. The first compound switch circuit may include a first field effect transistor (FET), where a drain of the first FET may be connected to the first power supply voltage. The first compound switch circuit may also include a second FET, where a source of the second FET may be connected to a source of the first FET, where a drain of the second FET may be connected to the output voltage supply node, where a gate of the first FET and a gate of the second FET may be connected together to form a first shared source node. The power supply control system may also include first voltage driving circuitry which may drive an “on” gate-to-source voltage level.