Boost Converter Mode Switching for Stable Low-Load Output
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Solution Overview
Problem
Switching power supplies face challenges in maintaining stable output voltage when the output load decreases, as pulse width modulation (PWM) arrangements may not function effectively, leading to unstable power delivery in low power usage scenarios.
Innovation Solution
A system that includes a circuit capable of switching between pulse width modulation (PWM) and pulse frequency modulation (PFM) modes, using threshold levels determined by digitized input and output voltages, and a selector device to adjust between these modes based on a timer signal, ensuring stable output voltage across varying loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PWM arrangement is used to accommodate varying output current, then the power supply can handle different output conditions, but the PWM arrangement may not work effectively when output load decreases below a predetermined threshold, leading to unstable power delivery
Solution Approach 1:
The system dynamically switches between PWM and PFM operating modes based on the output load condition. When the output load current exceeds the threshold, PWM mode is used for efficient voltage regulation. When the load current falls below the threshold, the system transitions to PFM mode to maintain stable power delivery, thus adapting to varying load conditions while ensuring reliability across the entire operating range.
2Power
If the width of voltage pulses is widened to accommodate increasing output current, then the power supply can deliver higher current, but the pulse width cannot become narrower when output load decreases, causing the PWM arrangement to fail
Solution Approach 1:
The system changes the fundamental operating parameter from pulse width modulation (PWM) to pulse frequency modulation (PFM) when the output load decreases below the threshold. In PWM mode, pulse width varies with load current. In PFM mode, the pulse frequency varies inversely with load current, allowing the system to maintain effective control across the full range of output power levels without the pulse width becoming stuck.
3Reliability
If a selector device and multiple threshold determination methods are added to switch between PWM and PFM modes, then stable output voltage is maintained across varying loads, but the device complexity increases
Solution Approach 1:
The system pre-determines two different threshold levels using different methods (digitized voltage calculation and direct analog measurement) and stores them in the selector device. Based on the startup condition and timer status, the appropriate threshold is selected in advance. This preliminary preparation allows the system to quickly switch between PWM and PFM modes without complex real-time calculations, maintaining voltage stability while limiting the increase in device complexity.
Data Source
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Figure 3A~3B
AI summary
A system includes a voltage booster circuit to receive an input voltage and provide an output voltage. A first device that is coupled to the voltage booster circuit to receive a digitized input voltage and a digitized output voltage and to determine, based on the digitized input voltage and the digitized output voltage, a first threshold level for the voltage booster circuit to operate in a pulse frequency modulation (PFM) mode. A second device that is coupled to the voltage booster circuit to receive the input voltage and the output voltage and to determine a second threshold level for the voltage booster circuit to operate in the PFM mode. A selector device that is coupled to the first device and the second device to select one of the first threshold level or the second threshold level for the voltage booster circuit.