PFC Switching Control Circuit for Input Current Waveform Shaping
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Solution Overview
Problem
Existing switching control circuits for power supply systems often experience a decrease in power factor due to the effects of diodes and inductors, which complicates the shaping of AC voltage and input current waveforms to be similar, leading to inefficiencies in power factor correction.
Innovation Solution
A switching control circuit that includes a target value output circuit and a drive signal output circuit, which control the transistor switching based on inductor current and output voltage, shaping the peak value of the inductor current to match the rectified voltage waveform, thereby improving the power factor by maintaining a proportional relationship with the AC voltage and ensuring the same cycle and phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a switching control circuit controls a transistor with constant on time to operate in critical mode, then the switching speed and responsiveness are improved, but the power factor decreases due to the effects of diode and inductor
Solution Approach 1:
The patent applies dynamics by transitioning from constant on-time control to variable on-time control. The on-time of the transistor is dynamically adjusted based on the instantaneous values of inductor current and rectified voltage, allowing the circuit to adapt to changing operating conditions and maintain optimal power factor correction across different load and line conditions.
Solution Approach 2:
The patent changes the control parameter from fixed on-time to variable on-time determined by the ratio of inductor current to rectified voltage. This parameter change enables the circuit to compensate for the effects of diode and inductor, improving power factor by adjusting the switching characteristics based on real-time circuit state.
2Productivity
If the transistor switching is controlled to operate in critical mode, then the efficiency is improved, but the waveform shaping of input current becomes distorted
Solution Approach 1:
The patent implements feedback control by continuously monitoring the inductor current and rectified voltage, and using their ratio to determine the transistor on-time. This feedback mechanism ensures that the input current waveform accurately follows the rectified voltage waveform, achieving both high efficiency and proper waveform shaping simultaneously.
Solution Approach 2:
The patent applies preliminary action by calculating and setting the appropriate on-time before each switching cycle based on the current operating conditions. This pre-determination of switching parameters ensures that the transistor switches at optimal moments, maintaining both efficiency and waveform quality.
3Loss of energy
If the on time of the transistor is extended to compensate for diode and inductor effects, then the power factor is improved, but the switching frequency decreases and response time increases
Solution Approach 1:
The patent uses dynamic control where the on-time is continuously adjusted based on the ratio of inductor current to rectified voltage. This dynamic adjustment allows the circuit to extend on-time only when necessary to compensate for diode and inductor effects, rather than using a fixed extended on-time, thus maintaining both power factor and response speed.
Solution Approach 2:
The patent changes the on-time parameter dynamically rather than using a fixed extended value. By adjusting the on-time based on real-time measurements of inductor current and rectified voltage, the circuit achieves power factor correction without the performance penalty of permanently extended switching periods.
Data Source
AI summary
A switching control circuit for a power supply circuit that generates an output voltage from an AC voltage. The power supply circuit includes a rectifier circuit rectifying the AC voltage, an inductor receiving the rectified AC voltage, and a transistor controlling an inductor current flowing through the inductor. The switching control circuit controls switching of the transistor, based on the inductor current and the output voltage. The switching control circuit includes a target value output circuit that outputs a target value of a peak value of the inductor current for shaping a waveform of the peak value so as to be similar to a waveform of the rectified voltage, and a drive signal output circuit that outputs a drive signal to turn on the transistor upon the inductor current falling below a predetermined value and turn off the transistor upon the peak value of the inductor current reaching the target value.