Switching Power Supply Light Load Phase Angle Control
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Solution Overview
Problem
Switching power supplies experience power factor degradation in the region of small phase angles under light load conditions due to maximum frequency limitations on switching frequency, leading to distorted input current waveforms and reduced inductor current.
Innovation Solution
A switching power supply with a control circuit that includes an ON width controlling means, zero current detecting means, load condition detecting means, and frequency reducing means to delay the turn ON timing of the switching element under light load conditions, maintaining the load condition over every period of the input voltage and reducing switching frequency, ensuring the phase angle of the input current is in phase with the input voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If maximum frequency limitation is applied to switching frequency under light load condition, then switching losses are reduced, but power factor degrades in the region of small phase angle
Solution Approach 1:
The switching frequency is dynamically adjusted based on the phase angle of the input voltage. The control circuit detects the phase angle and varies the switching frequency accordingly, applying frequency limitation only in specific phase angle regions where it does not degrade power factor, while maintaining high frequency in regions where power factor is already acceptable.
Solution Approach 2:
Different frequency control strategies are applied to different phase angle regions. The control circuit selectively applies maximum frequency limitation only in specific local regions (small phase angles) while maintaining normal frequency control in other regions, optimizing the balance between switching losses and power factor for each specific operating condition.
2Loss of energy
If switching frequency is limited to reduce switching losses, then efficiency improves, but input current waveform becomes distorted
Solution Approach 1:
The switching frequency is dynamically varied according to the instantaneous phase angle of the input voltage rather than applying a static frequency limit. This dynamic adjustment ensures that frequency limitation is applied only when and where it does not cause harmful current distortion, maintaining waveform quality while still reducing switching losses in appropriate regions.
Solution Approach 2:
The control circuit changes the switching frequency parameter based on the detected phase angle of the input voltage. By continuously monitoring and adjusting the frequency parameter in response to changing operating conditions, the system optimizes the trade-off between switching losses and current waveform quality across different operating regions.
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 effectively prevents power factor degradation by maintaining the phase angle alignment of the input current with the input voltage, reducing distortion and switching losses, even under maximum frequency limitations, thereby enhancing efficiency and power factor correction.
Implementation Method 1
a rectifier circuit for rectifying an input AC voltage
Implementation Method 2
a switching element forming a current path from the rectifier circuit through the inductor in an ON state of the switching element
Implementation Method 3
a zero current detecting means that detects zero current flowing through the switching element
Data Source
AI summary
A switching power supply that conducts switching of an input voltage by a switching element to obtain a specified output voltage includes: an ON width controlling component that controls an ON width of the switching element; a zero current detecting component that detects zero current through the switching element to turn ON the switching element; a frequency reducing component that delays a turn ON timing of the switching element upon detection of a light load condition by a load condition detecting component to reduce a switching frequency of the switching element; and an AC period detecting component that detects a period of the input voltage to hold the load condition detected by the load condition detecting component over every period detected by the AC period detecting component.