Power Converter Control for Low Ripple Across Supply Voltages
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Solution Overview
Problem
Power converter circuits face challenges in maintaining low output voltage ripple across a wide range of supply voltages, particularly as input supply voltage varies, leading to increased ripple voltage at lower supply voltages due to slower inductor current charging.
Innovation Solution
A power converter circuit with a controller that transitions to a high-side on state when the supply voltage is below a threshold, increasing switching frequency to reduce output current ripple, and disabling such transitions at higher supply voltages until output current reaches zero for recharge, thereby managing switching frequency and ripple voltage effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the input supply voltage increases, then the switching frequency is increased to lower the ripple voltage at the output, but at lower supply voltages the inductor current charging is slower resulting in lower switching frequency and increased ripple voltage
Solution Approach 1:
The patent implements dynamic switching frequency adjustment based on supply voltage conditions. The controller monitors the supply voltage and dynamically transitions between different operating modes (intermediate state, HSON state, and recharge state) to optimize the switching frequency. At low supply voltages, the controller enables direct transition to HSON state with higher switching frequency to maintain low ripple, while at higher supply voltages it uses conventional switching with lower frequency, thus adapting to different voltage conditions effectively.
2Object-affected harmful factors
If the switching frequency is increased at low supply voltages to reduce ripple voltage, then the output voltage ripple is reduced, but the inductor current charging time becomes insufficient leading to potential current limit violations
Solution Approach 1:
The controller performs preliminary assessment of supply voltage conditions before transitioning to HSON state. By monitoring the supply voltage and comparing it against threshold values, the controller determines in advance whether to enable direct transition to high-side on state or follow conventional switching sequence. This preliminary action ensures that high switching frequency is only applied when supply voltage conditions support adequate current charging, thus preventing current limit violations while reducing ripple.
3Reliability
If a fixed current limit threshold is set for discontinuous conduction mode operation, then the converter operates reliably within current limits, but the ripple for a given load is fixed and cannot be optimized across different supply voltages
Solution Approach 1:
The patent changes the operating parameters dynamically based on supply voltage conditions. Instead of using a fixed current limit threshold for all operating conditions, the controller adjusts the effective current limit by enabling direct transition to HSON state at low supply voltages. This parameter change allows the system to achieve lower ripple voltage at low supply voltages while maintaining current limit compliance through intelligent control logic that considers both current status and supply voltage conditions.
Data Source
AI summary
An example circuit includes a supply comparator having a supply input, a supply reference input and a supply comparator output. The supply input is coupled to a supply input terminal, and the supply reference input is configured to receive a supply reference voltage. A controller has a comparator input, a high-side output and a low-side output. The comparator input is coupled to the supply comparator output. A high-side switch having a control input. The high-side switch is coupled between the supply input and a switch output terminal, and the high-side output is coupled to the control input of the high-side switch. A low-side switch has a control input. The low-side switch is coupled between the switch output terminal and a ground terminal, and the low-side output is coupled to the control input of the low-side switch.