Flyback Over-Current Protection Module Adaptive Current Limiting
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Solution Overview
Problem
Conventional over-current protection devices for flyback power supplies have fixed current limits that are affected by varying input voltages, leading to inconsistent operation, potential damage, and high system costs due to the need for circuit adjustments and replacements, as well as output voltage ripples and power quality issues.
Innovation Solution
An over-current protection module that generates a compensation current based on a second duty cycle of a control signal, using a switch control unit, transformation unit, timing control unit, and current control unit to determine an over-current reference voltage, allowing for adaptive current limiting without affecting output voltage quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed current limit value is set for over-current protection, then the protection mechanism is simple to implement, but the operation quality is easily affected by different input voltages causing inconsistent protection performance
Solution Approach 1:
The patent implements dynamic current limit adjustment by using a compensation current that varies with the duty cycle. The current limit is no longer fixed but dynamically adapts to different operating conditions through the relationship between duty cycle and compensation current magnitude, resolving the contradiction between simple implementation and consistent performance.
Solution Approach 2:
The patent changes the parameter of current limit from a fixed value to a variable value that depends on the duty cycle. By establishing a relationship where the compensation current magnitude is determined by the duty cycle, the system automatically adjusts the current limit to maintain consistent protection performance across different input voltages.
2Reliability
If different current limit values are set for different input voltages, then the protection performance becomes consistent, but the circuit complexity increases and requires circuit adjustments for different conditions
Solution Approach 1:
The patent creates a universal protection mechanism that automatically adapts to different input voltages through a single circuit configuration. The compensation current generation circuit works universally across all operating conditions by deriving the compensation current from the duty cycle itself, eliminating the need for separate circuit adjustments for different voltage levels.
Solution Approach 2:
The system performs self-adjustment by using the duty cycle information to automatically generate the appropriate compensation current. The control circuit serves itself by extracting the necessary adjustment information from its own operation parameters (duty cycle) without requiring external intervention or additional sensing circuits for each voltage condition.
3Reliability
If compensation current is used to adjust initial values for different input voltages, then stable current cutoff is achieved, but jitter increases and output voltage quality deteriorates
Solution Approach 1:
The patent implements periodic compensation current injection synchronized with the switching cycle. By injecting the compensation current at specific periodic intervals (during the off-time of the switching element) and maintaining it only for the necessary duration, the system achieves stable current cutoff while minimizing disturbance to the output voltage through controlled, time-limited action.
Solution Approach 2:
The compensation current is generated in advance based on the duty cycle information before the over-current protection decision is made. This preliminary establishment of the compensation current allows the system to pre-calculate the appropriate current limit adjustment, enabling stable and predictable current cutoff without last-minute adjustments that could cause voltage ripples.
Data Source
AI summary
An over-current protection module for a flyback power supply having a transformer includes: a switch control unit, configured to generate a control signal in a first period to control a transistor switch coupled to a primary side of the transformer, wherein the transistor switch is turned on in a first duty cycle of the control signal and the transistor switch is turned off in a second duty cycle of the control signal; a transformation unit, configured to generate a compensation current according to the second duty cycle; a timing control unit, configured to output the compensation current to an impedance unit to generate an impedance cross voltage in a shut-off period of the transistor switch of the first period; and a current control unit, configured to determine an over-current reference voltage according to the impedance cross voltage for the over-current protection module in a second period following the first period.