Bootstrap Circuit Level Shifting for Low-Resistance High-Side MOSFET Drive
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Solution Overview
Problem
Existing bootstrap circuits in power supply devices, such as half-bridge DC/DC converters, face challenges in reducing the on-resistance of switching elements driven by a bootstrap voltage and simplifying timing control.
Innovation Solution
The proposed solution involves a bootstrap circuit configuration that includes a level shifter with a P-channel MOS field-effect transistor, a resistor, and an N-channel MOS field-effect transistor, which controls a P-channel MOS field-effect transistor based on the switching voltage and control signals, thereby reducing on-resistance and simplifying timing control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an N-channel MOS field-effect transistor is used as a high-side switching element to achieve low on-resistance and maximum efficiency, then the efficiency is improved, but the timing control complexity increases
Solution Approach 1:
The bootstrap circuit pre-charges the bootstrap capacitor during the off-state of the high-side switch, preparing the gate drive voltage in advance. This preliminary action ensures that when the switch needs to turn on, the gate already has sufficient voltage, simplifying the timing control while maintaining low on-resistance
Solution Approach 2:
The bootstrap circuit acts as an intermediary between the low-side switch control and the high-side switch gate drive. It transfers and transforms the control signals through the bootstrap capacitor and diode, providing the necessary gate voltage without requiring complex direct timing control
2Loss of energy
If a bootstrap circuit is used to drive the high-side N-channel MOS transistor, then the on-resistance is reduced, but the circuit complexity increases
Solution Approach 1:
The bootstrap circuit serves multiple functions: it generates the gate drive voltage for the high-side switch, provides isolation between the high-side and low-side controls, and enables the use of low-on-resistance N-channel MOS transistors. This multi-functionality justifies the added circuit elements by consolidating several requirements into a single circuit architecture
Solution Approach 2:
The bootstrap circuit is self-charging through the bootstrap diode and capacitor during the off-state of the high-side switch. Once charged, it automatically maintains the gate voltage without requiring external intervention, making the circuit self-sustaining and reducing the need for additional control complexity
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 configuration effectively decreases the on-resistance of N-channel MOS field-effect transistors driven by the bootstrap voltage and facilitates more straightforward timing control, enhancing the efficiency and performance of power supply devices.
Implementation Method 1
a capacitor CB having a first terminal to which a second terminal of the first switch is connected and a second terminal to which a switching voltage is applied
Implementation Method 2
a P-channel MOS field-effect transistor configured to have a gate to which the switching voltage is supplied
Data Source
AI summary
A bootstrap circuit includes a first switch configured to have a first terminal to which a constant voltage is applied, a capacitor configured to have a first terminal to which a second terminal of the first switch is connected and a second terminal to which a switching voltage is applied, and a controller configured to control the first switch based on the switching voltage and a control signal. The switching voltage is a voltage generated at a connection node between a first switching element and a second switching element. The second switching element is a switching element provided on a lower potential side with respect to the first switching element and configured to perform switching based on the control signal.