DC-DC Converter Constant-Charge Control for Stable Output Ripple
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Solution Overview
Problem
Existing DC-DC converters face challenges in maintaining consistent output voltage regulation and efficiency under varying line voltage conditions, particularly under light load conditions, where techniques like Continuous Conduction Mode and Adaptive Constant On-Time control are inefficient and complex.
Innovation Solution
A DC-DC converter with a control circuit that operates the high-side power switch in a constant charge mode, varying its on-time to maintain a constant charge transfer to the output capacitor, independent of input voltage fluctuations, using a peak inductor current threshold generator and peak current control circuit to adjust the peak inductor current based on input and output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Constant On-Time (COT) control is used, then fast and efficient control is achieved, but output voltage ripple varies with line voltage
Solution Approach 1:
The patent changes the control parameter from fixed on-time to variable on-time based on input voltage conditions. The controller adjusts the on-time parameter dynamically: using a first on-time value when input voltage is below a threshold and a second on-time value when input voltage is above the threshold, thereby maintaining consistent output voltage ripple across different line voltage conditions while preserving fast response characteristics
2Reliability
If Continuous Conduction Mode (CCM) control is used, then output voltage regulation is maintained, but efficiency degrades under light load conditions
Solution Approach 1:
The patent implements dynamic switching between different operating modes based on load conditions. The controller transitions from CCM to Pulse Frequency Modulation (PFM) mode when load current falls below a threshold, and adjusts the on-time parameter dynamically based on input voltage. This dynamic adaptation maintains reliable output voltage regulation across all load conditions while significantly improving efficiency under light loads by avoiding the continuous switching losses of CCM
3Adaptability or versatility
If Adaptive Constant On-Time (ACOT) control with integral loop is used, then line voltage adaptation is achieved, but system complexity and physical area increase
Solution Approach 1:
The patent extracts and removes the complex integral loop component from the control circuit, replacing it with a simplified threshold-based detection mechanism. The controller directly compares input voltage against a threshold and adjusts on-time accordingly, achieving line voltage adaptation without requiring integrators or complex feedback loops, thereby reducing both circuit complexity and physical area while maintaining adaptability
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 approach ensures consistent output voltage regulation and high efficiency across varying load conditions, reducing system complexity and output ripple, thereby improving overall performance.
Implementation Method 1
The inductor stores energy in its magnetic field when current flows through it and then releases that energy when the current flow is reduced or stopped
Implementation Method 2
The control circuit is configured to operate the high-side power switch in a constant charge mode of operation to vary on-time of the high-side power switch to maintain a constant amount of charge being transferred to the output capacitor during each charging cycle
Data Source
AI summary
Disclosed herein is a DC-DC converter, including a high-side power switch coupled between an input voltage and a switched node and a low-side power switch coupled between the switched node and ground. An inductor is coupled between the switched node and an output node. An output capacitor is coupled between the output node and ground. A control circuit is configured to operate the high-side power switch in a constant charge mode of operation to vary on-time of the high-side power switch to maintain a constant amount of charge being transferred to the output capacitor during each charging cycle, independent of variation of the input voltage.