Buck-Boost Controller With Valley Detection For Power Factor
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Solution Overview
Problem
High power-factor buck-boost converters operating in deep discontinuous conduction mode experience high peak and RMS current, leading to increased conduction and turn-off power losses, and variable switching periods result in input current distortion, necessitating improved control mechanisms to maintain high power factor and reduce losses.
Innovation Solution
A high power-factor buck-boost converter incorporates a valley detection circuit to control the switch, an error detector circuit to determine time durations, and a current sense circuit to manage output current, ensuring the quotient of squared time durations and sum of time durations remains constant over an AC line cycle, thereby regulating the switch's on and off periods to maintain unity power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the converter operates in deep discontinuous conduction mode with fixed switching period, then the circuit structure is simple, but high peak and RMS current occurs leading to increased conduction and turn-off power losses
Solution Approach 1:
The patent applies dynamics by making the switching period variable instead of fixed. The control circuit dynamically adjusts the switching period based on the valley detection signal and timing control, allowing the converter to operate optimally across different load and line conditions. This dynamic adjustment reduces peak and RMS current, thereby decreasing conduction and turn-off power losses while maintaining simplicity in circuit structure.
2Loss of energy
If variable switching period is used to reduce power losses, then power losses are minimized, but input current distortion increases
Solution Approach 1:
The patent employs feedback through valley detection and timing control. The valley detection circuit monitors the switching node voltage and generates a valley signal that feeds back to the control circuit. The control circuit uses this feedback to adjust the switching period and duty cycle, ensuring that power losses are minimized while input current distortion is kept within acceptable limits by continuously adapting to changing conditions.
3Loss of energy
If valley switching control is implemented to reduce peak current, then peak and RMS current are reduced, but switching period becomes variable causing input current distortion
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the switching period and duty cycle based on valley detection. Instead of maintaining a fixed switching period, the control circuit modifies these parameters in response to the valley signal, allowing the converter to reduce peak and RMS current while managing input current distortion through controlled parameter variation.
4Device complexity
If fixed on-time control is used, then control is simple, but high peak and RMS current occurs increasing power losses
Solution Approach 1:
The patent transitions from fixed on-time control to dynamic timing control based on valley detection. The control circuit dynamically determines the on-time and switching period based on the valley signal and timing control, rather than using a fixed on-time. This dynamic approach reduces peak and RMS current, thereby decreasing conduction and turn-off power losses while maintaining reasonable control complexity.
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 effectively reduces peak and RMS current, minimizes power losses, and maintains unity power factor by dynamically controlling the switch's operation, ensuring efficient energy transfer and reduced distortion in input current.
Implementation Method 1
a magnetic element (103) having a primary winding (PRI), and a secondary winding (SEC)
Implementation Method 2
a rectifier diode (105)
Data Source
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AI summary
A high power-factor buck-boost converter having a rectified low-frequency AC line voltage input and a DC output is provided. The converter may include a magnetic element (103), a controlled switch (102) having a gate terminal and a drain terminal that is coupled to the magnetic element, a rectifier (diode105) coupled to the magnetic element, an output smoothing capacitor (106) coupled to the rectifier diode, and a control circuit (199) having an output coupled to the gate terminal of the controlled switch for repeatedly turning the controlled switch off for a first time duration and on for a second time duration. The second time duration may be determined as a function of the first time duration immediately preceding the second time duration.