Boost Charge Circuit for High-Side N-Channel FET Gate Drive
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Solution Overview
Problem
DC-DC converters using an N-channel field effect transistor (FET) in the high-side driver often require an internal voltage higher than the input voltage to adequately turn on the FET, necessitating additional circuitry to drive the gate voltage above the source voltage, which can be complex and costly.
Innovation Solution
A boost charge circuit within the converter circuit charges a capacitor during a charging cycle, generating a voltage difference that is added to the input voltage to create a higher internal voltage, enabling the gate driver circuit to provide a higher output voltage range without the need for two high-voltage FETs and complex level shift circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an N-channel FET is used in the high-side driver, then the converter can achieve better performance, but an additional boost charge circuit is required to generate higher internal voltage
Solution Approach 1:
The patent combines the boost charge circuit functionality with the existing DC-DC converter circuitry by integrating shared components (inductor, switches, control logic) to generate the required higher internal voltage for the N-channel FET gate driver, eliminating the need for a separate standalone boost circuit
2Reliability
If a boost charge circuit is added to generate higher internal voltage, then the N-channel FET can be adequately turned on, but the circuit complexity and cost increase
Solution Approach 1:
The patent designs the boost charge circuit to serve multiple functions: it generates the higher voltage needed for the N-channel FET gate driver while simultaneously providing voltage regulation and sharing magnetic components with the main converter, making the added circuitry more justifiable through multiple benefits
3Reliability
If two high-voltage FETs and level shift circuits are used to drive the gate voltage above source voltage, then the FET can be turned on, but the circuit becomes more complex and costly
Solution Approach 1:
The patent extracts and eliminates the need for separate high-voltage FETs and level shift circuits by implementing an integrated boost charge circuit that directly generates the required gate drive voltage, removing unnecessary components while maintaining the essential gate drive capability
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 boost charge circuit simplifies the circuitry by generating a higher internal voltage, allowing the gate driver circuit to provide a higher output voltage range while reducing the complexity and cost associated with high-voltage FETs and level shift circuits.
Implementation Method 1
Boost charge circuits operate by storing electrical charge in a capacitor during a charging cycle. The stored charge produces a voltage difference between the two plates of the charged capacitor.
Data Source
AI summary
Described embodiments include a boost circuit for a DC-DC voltage converter includes a first transistor coupled between an input voltage terminal and a boost terminal. A second transistor is coupled between the first control terminal and a switch terminal, and has a second control terminal coupled to the switch terminal. A capacitor is coupled between the boost terminal and the switch terminal. A third transistor has a third control terminal and first and second current terminals. The first current terminal is coupled to the first control terminal, and the third control terminal is coupled to an internal voltage supply terminal. A fourth transistor is coupled between the internal voltage supply terminal and the second current terminal, and has a fourth control terminal coupled to a drive terminal.