Adaptive Boost Driver for Series Capacitor Buck Converter
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Solution Overview
Problem
In series capacitor buck converters, the nodal voltage on the transfer capacitor does not go to ground when the low side power switch is ON, causing the boost charging circuit to struggle with varying input voltages and system parameters, which affects the stable operation of the high side n-channel MOSFET.
Innovation Solution
An adaptive boost driver circuit is introduced, featuring a high side flying buffer driver with dynamically controlled voltage (VGX) that adjusts to maintain a constant voltage across the bootstrap capacitor, ensuring a stable power supply for the high side power switch irrespective of voltage variations across the transfer capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional boost charging circuit is used with a fixed voltage reference, then the circuit structure is simple, but the bootstrap capacitor voltage varies with input voltage changes, causing unstable operation of the high side power switch
Solution Approach 1:
The patent implements a feedback mechanism where the variable power supply voltage VGX is dynamically adjusted based on the voltage across the transfer capacitor Ct. The boost charging circuit monitors the actual voltage conditions and automatically modifies VGX to compensate for variations, ensuring the bootstrap capacitor maintains a stable voltage regardless of input voltage changes or load conditions.
Solution Approach 2:
The patent transitions from a static fixed voltage reference to a dynamic variable power supply VGX that adapts its output in real-time. The power supply voltage VGX is dynamically controlled to track and compensate for variations in the transfer capacitor voltage, making the bootstrap capacitor voltage stable under varying operating conditions without requiring a complex fixed-voltage reference circuit.
2Adaptability or versatility
If the boost charge voltage is fixed, then the power supply circuit is simple, but it cannot adapt to varying voltage on the transfer capacitor, leading to unstable bootstrap capacitor voltage
Solution Approach 1:
The patent changes the key parameter of the power supply from a fixed voltage to a variable voltage VGX that can adapt its output level. By dynamically adjusting the power supply voltage VGX based on the transfer capacitor voltage conditions, the system achieves adaptability to varying operating parameters while maintaining a relatively simple power supply circuit architecture.
3Reliability
If a variable power supply voltage VGX is used to maintain constant bootstrap capacitor voltage, then the high side power switch operates stably, but the circuit complexity increases
Solution Approach 1:
The variable power supply VGX serves multiple functions simultaneously: it charges the bootstrap capacitor, compensates for transfer capacitor voltage variations, and ensures stable operation of the high side power switch. By consolidating these functions into a single adaptive power supply unit, the circuit achieves reliable operation with minimal additional 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 solution maintains a stable 5V voltage across the bootstrap capacitor and buffer driver, providing a fixed safe operating voltage for the high side power switch, even as the voltage across the transfer capacitor varies, thus ensuring reliable operation of the series capacitor buck converter.
Implementation Method 1
whose positive and negative power supply terminals are connected to the positive (+) terminal and reference (−) terminal of its bootstrap capacitor, CA
Implementation Method 2
The VGX voltage is coupled to the positive terminal of the bootstrap capacitor, CA. As the voltage across Ct varies, VGX adjusts in order to maintain a relatively constant voltage, 5V for example, across CA
Data Source
AI summary
A power circuit combination includes a series capacitor buck converter including a first half-bridge including a first high side power switch (HSA), first low side power switch (LSA) and a second half-bridge. A transfer capacitor (Ct) is connected in series with HSA and LSA, and between the first and second half-bridges. An adaptive HS driver circuit has an output coupled to a gate of HSA and includes a power supply circuit including a summing circuitry that dynamically outputs a variable power supply level (VGX) based on a fixed voltage and a voltage across Ct, a buffer driver, and a boost capacitor (CA) across the buffer driver. VGX is coupled to a positive terminal of CA. The power supply circuit is configured so that as a voltage across Ct varies, VGX adjusts so that a voltage across CA is changed less than a change in voltage across Ct.