Bootstrap Capacitor Charging for Low-Voltage Switch Drive
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Solution Overview
Problem
Conventional power converters using n-type transistors face poor conduction efficiency of high-side switches when input voltage is low due to the need for a bootstrap capacitor, which increases the circuit area and reduces switch performance.
Innovation Solution
The power converter incorporates a low-capacitance bootstrap capacitor inside the circuit, connected to a charging circuit that charges the capacitor to provide high driving voltages for the high-side and low-side switches, ensuring efficient operation even at low input voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bootstrap capacitor is used to drive the high-side switch, then the switch can be conducted, but the conduction efficiency is poor when input voltage is low
Solution Approach 1:
The patent changes the voltage parameter by introducing a charging circuit that charges the bootstrap capacitor to a voltage higher than the input voltage. This voltage boosting allows the high-side switch to achieve good conduction efficiency even when the input voltage is low, resolving the contradiction between reliable switch conduction and maintaining conduction efficiency under low voltage conditions
2Quantity of substance
If a bootstrap capacitor with high capacitance is used outside the power convertor, then it can provide sufficient charge, but the area occupied on the circuit board increases
Solution Approach 1:
The patent merges the bootstrap capacitor with the power convertor by placing it inside the convertor package rather than outside on the circuit board. This integration allows the use of a low-capacitance capacitor (since the charging circuit provides sufficient charge) while minimizing the area occupied on the circuit board, effectively resolving the contradiction between charge capacity and board area
3Area of stationary object
If a low-capacitance bootstrap capacitor is used inside the power convertor, then the area occupied is minimized, but sufficient charge must be provided for switch conduction
Solution Approach 1:
The patent applies preliminary action by using the charging circuit to charge the bootstrap capacitor to a high voltage level before the high-side switch needs to conduct. This pre-charging ensures that even though the capacitor has low capacitance (minimizing area), it stores sufficient charge to provide effective gate drive for the high-side switch during its conduction period
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 solution maintains high conduction efficiency for both switches by using a low-capacitance bootstrap capacitor, occupying minimal space and ensuring successful switching operations, thus enhancing the power converter's operational efficiency.
Implementation Method 1
A first terminal of the bootstrap capacitor is connected to the driver circuit. A second terminal of the bootstrap capacitor is connected to the second terminal of the high-side switch. The charging circuit is connected to the first terminal of the bootstrap capacitor. The charging circuit is configured to charge the bootstrap capacitor.
Data Source
AI summary
A power convertor increasing driving voltages of switches is provided. The power convertor includes a high-side switch, a low-side switch, a driver circuit, a bootstrap capacitor and a charging circuit. The driver circuit is connected to a control terminal of the high-side switch and a control terminal of the low-side switch. A first terminal of the bootstrap capacitor is connected to the driver circuit and the charging circuit. The charging circuit charges the bootstrap capacitor, and the driver circuit drives the high-side switch and the low-side switch by using a voltage of a first terminal of the bootstrap capacitor.