SMPS Power Factor Correction via Valley Voltage Detection
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Solution Overview
Problem
Switching-mode power supplies (SMPS) face challenges in optimizing power factor when driving a light load, as the waveform of the average input current differs from the filtered input voltage, leading to suboptimal power factor performance.
Innovation Solution
The apparatus includes a line voltage detector and an ON time controller with a valley voltage detector, which provides a scaled voltage representing the line voltage and controls the ON time of the power switch to ensure the average input current is proportional to the AC input voltage, optimizing power factor by adjusting the ON time based on the valley voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a SMPS uses a low-pass filter in the anti-EMI circuit, then electromagnetic interference is reduced, but the power factor deteriorates under light load conditions
Solution Approach 1:
The patent applies preliminary action by detecting the valley voltage of the input voltage in advance and using it to pre-set the ON-time of the power switch. This allows the system to proactively compensate for the waveform distortion caused by the low-pass filter before it affects the power factor, rather than reacting after the problem occurs. The valley voltage detection and ON-time adjustment happen in advance to ensure proper current waveform alignment.
Solution Approach 2:
The patent implements feedback by continuously monitoring the input voltage and using the detected valley voltage to adjust the power switch ON-time. The system feeds back the voltage information through the control circuit to dynamically modify the switching parameters, creating a closed-loop control that maintains optimal power factor despite the presence of the low-pass filter in the anti-EMI circuit.
2Loss of energy
If a SMPS operates under light load conditions, then energy consumption is reduced, but power factor optimization becomes difficult
Solution Approach 1:
The patent applies dynamics by making the power switch ON-time variable rather than fixed. The control circuit dynamically adjusts the ON-time based on the detected valley voltage of the input voltage, allowing the system to adapt its operating parameters in real-time according to load conditions. This dynamic adjustment enables maintaining good power factor even when operating under varying light load conditions.
Solution Approach 2:
The patent implements parameter changes by modifying the ON-time parameter of the power switch based on the input voltage characteristics. By changing the ON-time parameter in response to valley voltage detection, the system adjusts its operating parameters to maintain optimal power factor under different load conditions, particularly under light load where power factor optimization is most challenging.
Data Source
AI summary
An apparatus is capable of improving the power factor of a power supply powered by a high power line and a ground power line. The apparatus comprises a line voltage detector and an ON time controller. The line voltage detector provides a scaled voltage to represent a line voltage of the high power line. The ON time controller has a valley voltage detector, which provides, in response to the scaled voltage, a valley representative representing a valley voltage of the line voltage. The ON time controller controls an ON time of a power switch in the power supply in response to the valley representative.