Secondary Controlled AC-DC Converter Low Frequency Operation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flyback AC-DC converters operate inefficiently at low frequencies due to dedicated primary-side oscillators and require separate oscillators for soft-start operations, leading to increased size, complexity, and cost.
Innovation Solution
Implementing a secondary-controlled AC-DC converter with an independent oscillator on the primary-side controller that switches between open-loop and close-loop modes using a gate-drive signal from the oscillator and PWM signals from the secondary-side controller, allowing for efficient low-frequency operation without a dedicated primary-side oscillator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated primary-side oscillator is used for soft-start operations, then the converter can operate during startup and standby modes, but the size, complexity, and cost of the converter increases
Solution Approach 1:
The patent merges the soft-start oscillator function with the secondary-side controller by allowing the secondary-side controller to generate gate-drive signals directly during startup and standby modes. This eliminates the need for a separate dedicated primary-side oscillator, reducing device complexity while maintaining operational reliability during all modes including startup and standby.
Solution Approach 2:
The secondary-side controller is designed to perform multiple functions: it controls the synchronous rectifier during normal operation and also generates gate-drive signals for the primary power switch during startup and standby modes. This multi-functionality eliminates the need for dedicated separate circuits, reducing overall converter complexity while maintaining full operational capability.
2Ease of operation
If a dedicated primary-side oscillator is used, then soft-start operations can be performed, but the converter operates inefficiently at low frequencies
Solution Approach 1:
The patent implements dynamic operation where the converter switches between different control modes based on operational state. During startup and standby, the secondary-side controller generates gate-drive signals at appropriate low frequencies. During full operation, it transitions to PWM control. This dynamic adaptation allows efficient low-frequency operation during standby while maintaining high efficiency during full load operation.
Solution Approach 2:
The control frequency and mode are changed based on operational requirements. The secondary-side controller adjusts its output frequency and control strategy according to the operational phase (startup, standby, or full operation), enabling efficient low-frequency operation during standby modes while maintaining optimal performance during full operation.
3Reliability
If separate oscillators are used for soft-start and PWM operations, then each function can be optimized, but the converter size and cost increase
Solution Approach 1:
The patent combines multiple oscillator functions into a single secondary-side controller that can generate both soft-start gate-drive signals and PWM control signals as needed. This consolidation reduces the number of separate components, decreasing converter size and cost while maintaining the ability to optimize each operational mode through appropriate control strategies.
Solution Approach 2:
The secondary-side controller is designed as a universal control unit that performs multiple functions: generating gate-drive signals during startup, providing PWM control during operation, and managing standby modes. This multi-functional design eliminates the need for separate dedicated oscillators, reducing overall converter size and cost.
Data Source
AI summary
A secondary controlled AC-DC converter including an oscillator in a primary-side controller (PSC), and method for operating the same to enable soft-start and low frequency operation are provided. Generally, the method includes driving a power switch coupled between an AC input and a primary-side of the converter with a gate-drive (GD-signal). At startup and following auto-restart the GD-signal is generated using an oscillator-signal from the oscillator. After receiving start-stop pulses from a secondary-side controller, the oscillator-signal is decoupled from the GD-signal using a controller in the PSC, and the PSC begins generating the GD-signal using pulse-width-modulated (PWM) generated using the start-stop pulses. The oscillator operates at a first frequency independent of the PWM signal. The PWM signal includes one of a number of frequencies selected based on a power drawn from the converter, and, in low power applications can be less than the first frequency.