DC-DC Converter Bootstrap Circuit for Discontinuous Mode Stability
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Solution Overview
Problem
Conventional DC-DC converters face issues with high-side transistors becoming non-conductive at the wrong time due to higher conductive impedance, especially in discontinuous conduction mode, where the voltage supplied to the gate is lower than in continuous conduction mode.
Innovation Solution
The DC-DC converter design includes a high-side transistor and a low-side transistor with an anti-shoot-through circuit and a driver system that ensures the low-side transistor becomes conductive before the high-side transistor, using a capacitor to generate a drive voltage that maintains the high-side transistor's conductivity by applying a voltage equal to or greater than the power supply voltage plus the input voltage to the gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the conventional DC-DC converter operates in discontinuous conduction mode, then the voltage supplied to the gate of the high-side transistor is lower, but the conductive impedance of the high-side transistor becomes higher causing non-conduction
Solution Approach 1:
The low-side transistor is made conductive before the high-side transistor to preliminarily establish a reference voltage level. This preliminary action ensures that when the high-side transistor needs to conduct, the bootstrap capacitor has already charged to the appropriate voltage level, guaranteeing sufficient gate drive voltage regardless of whether the converter is in continuous or discontinuous conduction mode.
Solution Approach 2:
The bootstrap capacitor is used to cushion the voltage supply to the high-side transistor gate. By charging this capacitor beforehand during the low-side transistor conduction period, the system prepares a voltage reserve that compensates for potential voltage drops in discontinuous conduction mode, ensuring the high-side transistor receives adequate gate drive voltage when needed.
2Reliability
If the low-side transistor becomes conductive before the high-side transistor, then the drive voltage is maintained at power supply voltage plus input voltage, but requires precise timing control
Solution Approach 1:
The driver circuit monitors the conduction state of the transistors and adjusts the timing of gate drive signals accordingly. By using feedback from the node voltage (which reflects the conduction state), the driver ensures that the low-side transistor is activated first to charge the bootstrap capacitor, then subsequently activates the high-side transistor at the appropriate moment, maintaining reliable voltage levels without overly complex external timing control.
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 design prevents non-conduction of the high-side transistor when it is supposed to be conductive, maintaining high conductive impedance and ensuring stable operation in both continuous and discontinuous conduction modes.
Implementation Method 1
a boot strap circuit including a capacitor C105 and a diode D106... the capacitor C105... supplying the output unit with the drive voltage based on the capacitor
Data Source
AI summary
A first power supply line and having a first conductivity type a second transistor coupled between the first transistor and a second power supply line, and having the first conductivity type an output unit driving a first control signal causing the first transistor to become conductive, based on a drive voltage, and outputting the first control signal to the first transistor and a boot strap circuit including a capacitor having a first end coupled to a node of the first transistor and the second transistor and supplying the output unit with the drive voltage based on the capacitor, wherein an electric potential of the first end is reduced before the first transistor becomes conductive.