Primary Side Converter EFT Immunity Circuit Structure
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Solution Overview
Problem
Conventional primary side converters exhibit poor EFT immunity, leading to unstable output voltages due to transient disturbances, causing false feedback judgments and decreased performance during operations like inductive load switching or relay contact bounce.
Innovation Solution
A circuit structure enhancing EFT immunity, comprising a power ground, feedback voltage and current detecting blocks, a controller, PWM driver, and OR gate, which detects abrupt changes in feedback voltage and adjusts off-time and OCP threshold values to prevent output voltage drops by controlling the power MOS transistor's on-time and off-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional feedback voltage detection is used, then the converter operates normally under stable conditions, but the converter exhibits poor EFT immunity and makes wrong judgments during transient disturbances
Solution Approach 1:
The feedback voltage detection function is segmented into multiple independent detection paths: a first detection path for normal operation and a second detection path for transient disturbance detection. This segmentation allows the system to handle different operating conditions separately, improving EFT immunity without requiring complete redesign of the feedback system.
Solution Approach 2:
A transient disturbance detection circuit is introduced as an intermediary component between the feedback voltage and the controller. This intermediary detects transient disturbances and generates control signals to prevent the controller from making wrong judgments, thereby improving reliability without directly modifying the core control logic.
2Reliability
If the chip samples false feedback voltage values during EFT, then the output voltage decreases below acceptable ranges, but adding protection circuits increases device complexity
Solution Approach 1:
The transient disturbance detection circuit performs preliminary detection of potential EFT disturbances before they can affect the output voltage. By detecting the disturbance early and generating preventive control signals, the system avoids the need for complex corrective measures after voltage deviation occurs.
Solution Approach 2:
A dedicated feedback path is implemented that provides transient disturbance information to the controller. This feedback mechanism allows the controller to adjust its operation in real-time based on detected disturbances, maintaining output voltage stability without requiring overly complex protection circuits.
3Speed
If the converter responds quickly to feedback voltage changes, then dynamic response is improved, but susceptibility to transient disturbances increases
Solution Approach 1:
The system dynamically adjusts its response characteristics based on operating conditions. During normal operation, the converter responds quickly to feedback changes for fast dynamic response. During transient disturbances, the detection circuit modifies the response to filter out false signals, effectively making the system's behavior adaptive to different conditions.
Solution Approach 2:
The detection circuit monitors parameters such as voltage change rate and magnitude to distinguish between legitimate load changes and transient disturbances. By changing detection thresholds and response parameters based on the nature of the input signal, the system maintains fast response to valid changes while ignoring transient noise.
Data Source
AI summary
The present disclosure relates to a circuit structure for enhancing EFT immunity of primary side converter, including a power ground and a feedback voltage detecting block, a feedback current detecting block, a controller, a PWM driving block, a high voltage starting block, a starting unit, a circuit for enhancing EFT immunity of primary side converter, a power MOS transistor, and an OR gate configured to perform a logical OR of an off-time calculated theoretically and an off-time output by an off-time control block. The present disclosure enhances EFT immunity effectively and improves the dynamic characteristics of the primary side converter.