Half-Bridge Bootstrap Circuit With Cuk Negative Gate Bias
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Solution Overview
Problem
Conventional bootstrap circuits for half-bridge converters face issues with parasitic turn-on due to voltage increases during turn-off, leading to potential destruction of high-side transistors and increased power loss, especially with silicon carbide transistors, and are sensitive to duty cycle changes, which can damage the gate of the high-side transistor.
Innovation Solution
A half-bridge converter with a Cuk converter-based bootstrap circuit that operates in Discontinuous Voltage Mode (DVM) to provide a negative voltage to the high-side transistor gate, reducing dependence on the duty cycle, using a diode, capacitors, and inductors to generate a negative voltage with specific inductance and capacitance values, and optionally including a Zener diode to limit voltage amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional bootstrap circuit with diode and capacitor is used to control the high-side transistor gate voltage, then the circuit structure is simple, but voltage increases during turn-off cause parasitic turn-on leading to transistor destruction and increased power loss
Solution Approach 1:
The patent changes the electrical parameters of the bootstrap circuit by introducing a Cuk converter that generates a negative voltage component. This parameter change (adding negative voltage) modifies the gate voltage waveform to prevent parasitic turn-on, resolving the contradiction between simple circuit structure and reliable transistor operation
Solution Approach 2:
The Cuk converter acts as an intermediary device between the power source and the high-side transistor gate driver. It mediates the voltage delivery by converting the positive voltage into a waveform that includes a negative component, thereby preventing parasitic turn-on without requiring fundamental changes to the transistor or driver architecture
2Reliability
If a buck-boost circuit is used to provide negative drive voltage, then parasitic turn-on risk is reduced, but the negative voltage value becomes dependent on duty cycle causing gate damage when maximum rating is exceeded
Solution Approach 1:
The patent changes the voltage conversion topology from buck-boost to Cuk converter. This parameter change fundamentally alters the voltage relationship, making the negative voltage output independent of the duty cycle while maintaining parasitic turn-on prevention capabilities
Solution Approach 2:
The Cuk converter inverts the traditional approach by using an inductor-capacitor-diode network that naturally produces a negative voltage output regardless of duty cycle variations, rather than relying on switching ratios to generate the negative voltage component
3Reliability
If a Zener diode is added to limit voltage swings at the gate, then gate protection is improved, but power loss increases
Solution Approach 1:
The Cuk converter performs preliminary action by pre-shaping the gate voltage waveform to include a negative component that actively prevents parasitic turn-on. This eliminates the need for reactive protection devices like Zener diodes, thereby protecting the gate without the associated power loss
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 effectively reduces the risk of parasitic turn-on and power loss by stabilizing the negative voltage, making it less dependent on duty cycle changes, thereby protecting the high-side transistor and improving converter efficiency.
Implementation Method 1
The Cuk converter comprises a first and a second inductor, a switch, a first and a second capacitor and a diode to output the negative voltage
Implementation Method 2
The Cuk converter comprises a first and a second inductor, a switch, a first and a second capacitor and a diode to output the negative voltage
Implementation Method 3
The Cuk converter comprises a first and a second inductor, a switch, a first and a second capacitor and a diode to output the negative voltage
Data Source
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AI summary
The invention relates to half-bridge converter comprising a high-side transistor (Q1) connected to the positive electrode of a DC voltage source (VDC), a low-side transistor (Q2) connected to a reference ground (GND), a gate driver (GD) for controlling the high-side and low-side transistors (Q1, Q2) at a duty cycle (D) of the gate driver control signal, and a bootstrap circuit for providing a positive voltage (V+) and a negative voltage (V-) to the high-side transistor gate driver (GD). The bootstrap circuit comprises a first diode (D1), a first capacitor (C1) and a Cuk converter. The Cuk converter comprises a first and a second inductor (L1, L2), a switch (Q1; Q3), a first and a second capacitor (C2, C3) and a diode (D2) to output the negative voltage (V-) to the high-side transistor gate driver. The value of the inductance of the first and second inductors (L1, L2) and the value of the capacitance of the first capacitor (C2) of the Cuk converter are set such that the Cuk converter is configured to output said negative voltage when operating in a Discontinuous Voltage Mode (DVM).