High-Side Gate Driver 100% Duty Ratio Bootstrap Charging
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Solution Overview
Problem
The existing switching circuits cannot maintain a high-side transistor in an ON state over multiple switching cycles due to the inability of the bootstrap capacitor to charge without a switching operation, limiting the duty ratio to less than 100%.
Innovation Solution
A high-side gate driver is designed with a switching terminal, a bootstrap terminal, a common line, a reference line, a selection circuit, a regulator, a charge pump circuit, and a rectifying element to generate and stabilize voltages that allow the high-side transistor to be kept ON, along with an overvoltage protection circuit to prevent excessive voltage application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a bootstrap circuit is used to generate gate voltage higher than input voltage, then the high-side transistor can be turned on, but the bootstrap capacitor cannot be charged without switching operation, limiting duty ratio to less than 100%
Solution Approach 1:
The gate driver is divided into two independent power supply paths: a bootstrap circuit for normal switching operation and a dedicated overvoltage power supply circuit for charging the bootstrap capacitor. This segmentation allows the bootstrap capacitor to be charged independently of switching operations, enabling 100% duty ratio operation.
Solution Approach 2:
The overvoltage power supply circuit pre-charges the bootstrap capacitor to a voltage higher than the input voltage before switching operations begin. This preliminary charging action ensures that the bootstrap capacitor is always ready to provide sufficient gate voltage, even when the high-side transistor remains continuously ON.
2Device complexity
If the bootstrap capacitor is charged during switching operation, then the circuit structure is simple, but the high-side transistor cannot be kept ON over multiple switching cycles
Solution Approach 1:
An overvoltage detection circuit acts as an intermediary to monitor the input voltage and control the charging of the bootstrap capacitor. When overvoltage is detected, the detection circuit activates the overvoltage power supply circuit to charge the bootstrap capacitor, ensuring sufficient gate voltage is available for continuous ON operation.
3Productivity
If a charge pump circuit is added to enable 100% duty ratio operation, then the high-side transistor can be kept ON continuously, but the circuit complexity increases
Solution Approach 1:
The overvoltage power supply circuit serves multiple functions: it charges the bootstrap capacitor to enable 100% duty ratio operation, provides overvoltage protection by limiting the maximum charging voltage, and eliminates the need for external charging circuits. This multi-functionality justifies the added circuit complexity by providing comprehensive solution to multiple problems.
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 enables the high-side transistor to be kept ON at a duty ratio of 100%, improving efficiency and preventing power wastage by stabilizing voltages and managing overvoltage conditions effectively.
Implementation Method 1
a charge pump circuit provided between the common line and the reference line, the charge pump circuit being structured to step up a voltage difference between the common line and the reference line
Implementation Method 2
a rectifying element structured to charge a bootstrap capacitor provided between the bootstrap terminal and the switching terminal, with an output voltage of the charge pump circuit
Data Source
AI summary
A selection circuit generates a voltage VS of a switching terminal VS or a power supply voltage VCC, whichever is higher, in a common line. A regulator stabilizes a voltage VCOML of a reference line at a level lower than a voltage VCOM of the common line by a predetermined voltage difference ΔV. A charge pump circuit is provided between the common line and the reference line and steps up a voltage difference ΔV between the common line and the reference line. A rectifying element charges a bootstrap capacitor between a bootstrap terminal and the switching terminal, with an output voltage of the charge pump circuit.