Flyback Converter Control Circuit for Power Factor Correction
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Solution Overview
Problem
Conventional power factor correction (PFC) schemes in power converters require multiple stages, increasing circuit size and cost, and involve complex control methods that require sampling the input voltage and using analog multipliers, leading to inefficiencies and increased chip area.
Innovation Solution
A control circuit for flyback and AC-DC power converters that integrates power factor correction and pulse-width modulation (PWM) control, using a turn-on and turn-off signal generating circuit to maintain input current and voltage in phase, and output signal constant, eliminating the need for separate PFC stages and input voltage sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional power factor correction schemes are used, then power factor correction can be achieved, but circuit size and cost increase due to multiple stages
Solution Approach 1:
The patent combines power factor correction function and PWM control function into a single control circuit. The control circuit includes a turn-on signal generating circuit that detects drain-source voltage and generates turn-on signals, and a turn-off signal generating circuit that uses feedback error signals to generate turn-off signals. This integration eliminates the need for separate PFC stages, reducing circuit size while maintaining power factor correction performance.
Solution Approach 2:
The control circuit performs multiple functions simultaneously: it generates turn-on signals based on drain-source voltage detection, generates turn-off signals based on feedback error signals, maintains input current and voltage in phase, and maintains constant output electrical signals. This multi-functionality replaces conventional multi-stage architectures with a single unified control system.
2Reliability
If conventional PFC schemes with input voltage sampling and analog multipliers are used, then power factor correction can be achieved, but chip area increases
Solution Approach 1:
The patent extracts and eliminates the need for input voltage sampling circuits and analog multipliers from the conventional PFC scheme. Instead, the turn-on signal generating circuit directly detects drain-source voltage to generate turn-on signals, and the turn-off signal generating circuit uses feedback error signals directly. This removal of unnecessary components significantly reduces chip area while maintaining power factor correction functionality.
3Reliability
If conventional control methods are used, then power factor correction can be achieved, but control complexity increases
Solution Approach 1:
The patent applies different control strategies to different parts of the switching cycle: the turn-on signal generating circuit operates based on drain-source voltage detection during the off-state, while the turn-off signal generating circuit operates based on feedback error signals during the conducting state. This localized control approach simplifies the overall control logic compared to conventional unified control methods.
Data Source
AI summary
The present invention relates to control circuits and methods for a flyback converter and AC-DC power converters thereof. In one embodiment, a control circuit can include: (i) a turn-on signal generating circuit that is configured, in each switching cycle, to receive a drain-source voltage of a power switch of the flyback converter, and to activate a turn-on signal to turn on the power switch when the drain-source voltage reaches a valley value; (ii) a turn-off signal generating circuit that is configured, in each switching cycle, to activate a turn-off signal to turn off the power switch based on a power switch feedback error signal after a power switch conducting time interval has elapsed; and (iii) where input current and voltages of the flyback converter can be maintained as substantially in phase, and an output electrical signal of the flyback converter can be maintained as substantially constant.