Offline Converter Power Factor Circuit With DC Blocking
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Solution Overview
Problem
Conventional power-factor-improving methods for offline converters fail to accurately control the output current due to the influence of the DC component of the input voltage, leading to variations in the dimming signal and resulting power factor.
Innovation Solution
A power-factor-improving circuit comprising a voltage detector that blocks the DC component of the input voltage and generates a detection signal proportional to the AC component, combined with a DC bias circuit to create a dimming signal that accurately controls the output current, ensuring a high power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If serially connected resistors are used to divide the input voltage for generating the dimming signal, then the power factor is improved, but the output current control accuracy deteriorates due to DC component influence
Solution Approach 1:
The patent segments the input voltage signal processing into two independent paths: one path extracts the AC component for power factor improvement, while the other path provides a stable DC reference for accurate output current control. This segmentation eliminates the interference between DC component variations and dimming signal accuracy.
Solution Approach 2:
The patent extracts only the AC component of the input voltage signal using a coupling capacitor, separating it from the DC component. This extracted AC signal is then used to generate the dimming signal, while the DC component is excluded from influencing the output current control, thereby resolving the contradiction between power factor improvement and control accuracy.
2Loss of energy
If the dimming signal contains the AC component of input voltage for high power factor, then the power factor is improved, but the output current varies with input voltage DC component
Solution Approach 1:
The patent introduces a coupling capacitor as an intermediary element that allows the AC component of the input voltage to pass through for dimming signal generation while blocking the DC component from affecting the output current control. This intermediary enables simultaneous achievement of high power factor and stable output current.
Solution Approach 2:
The patent segments the signal processing to separate AC component utilization (for power factor) from DC component exclusion (for current stability). The coupling capacitor creates a clear division where AC signals are transmitted for improving power factor, while DC variations are blocked from affecting output current stability.
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
The solution allows for precise control of the output current and achieves a high power factor by isolating the DC component and using the AC component to determine the dimming signal, thereby stabilizing the output current regardless of input voltage variations.
Implementation Method 1
The voltage detector blocks the DC component of the input voltage of the offline converter and detects the AC component of the input voltage
Data Source
AI summary
A power-factor-improving circuit and method for an offline converter block the DC component and obtain the AC component of an input voltage of the offline converter. The AC component is superpositioned onto a DC bias signal to generate a dimming signal for the offline converter to adjust an output current of the offline converter. The offline converter has a high power factor due to the dimming signal with the AC component of the input voltage. In addition, the average of the dimming signal is determined by the DC bias signal, hence the output current can be precisely controlled according to the DC bias signal.