Switching Regulator ON-Time Control for THD and PF Compensation
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Solution Overview
Problem
Power factor correction (PFC) technologies in switching regulators face challenges with increased total harmonic distortion (THD) and worsened sinusoidal input current due to inverse inductor current around the valley of AC input voltage, affecting power factor (PF).
Innovation Solution
A switching regulator design that includes a power stage and control circuit to adjust the ON time duration of the main power switch based on AC input voltage and load current, incorporating THD and PF compensation mechanisms, using proportional integral circuits, basic ON time duration units, THD and PF compensate circuits, and logical units to generate control signals for optimal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If power factor correction (PFC) technology is used to prevent pollution to the power grid, then power factor is improved, but total harmonic distortion (THD) worsens due to the influence of the inverse inductor current around the valley of the alternating current (AC) input voltage
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the ON time duration of the main power switch based on the instantaneous value of the AC input voltage. The control circuit modifies the duty cycle parameter in response to voltage variations, particularly around the valley region, to simultaneously improve power factor and reduce total harmonic distortion. This is achieved through the equation: ON time duration = basic time duration + (THD compensate time duration × first coefficient) + (PF compensate time duration × second coefficient), where coefficients are adjusted based on operating conditions.
2Ease of manufacture
If the AC input voltage increases from its valley, then the power factor changes, but the sinusoidal degree of the input current worsens due to the influence of the safety capacitor and the input capacitor
Solution Approach 1:
The control circuit dynamically changes the ON time duration parameter in response to AC input voltage variations. As voltage increases from the valley, the control circuit adjusts the duty cycle to compensate for the adverse effects of safety and input capacitors on the sinusoidal degree of input current, thereby maintaining both power factor and current waveform quality.
Solution Approach 2:
The control circuit implements feedback by continuously monitoring the AC input voltage and adjusting the main power switch ON time duration accordingly. This closed-loop control ensures that the regulator responds to voltage changes and maintains optimal power factor and sinusoidal current characteristics across varying operating conditions.
Data Source
AI summary
A switching regulator converts an AC input voltage into an output voltage, to power a load. The switching regulator includes a power stage having a main power switch. The main power switch has different ON time durations under different AC input voltage conditions and different load currents.