Flyback Switching Power Supply Overcurrent Protection Circuit
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Solution Overview
Problem
Existing flyback switching power supply devices face challenges in regulating overcurrent peak current due to fluctuations in AC input voltage, particularly when using oscillators with frequency modulating functions, leading to increased circuit complexity and costs.
Innovation Solution
A control circuit for flyback switching power supply devices that includes a current detecting circuit, an overcurrent protection circuit, a voltage correction circuit, and a slope compensation circuit, which corrects the reference voltage signal based on the slope compensation signal to maintain consistent overcurrent protection levels regardless of AC input voltage fluctuations, and modulates the switching frequency using an oscillator with a frequency modulating function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an oscillator with frequency modulating function is used to regulate switching frequency, then the switching frequency can be modulated to reduce EMI noise, but the overcurrent protection level fluctuates with AC input voltage changes
Solution Approach 1:
The patent employs feedback mechanisms where the overcurrent protection circuit continuously monitors the actual current through the switching element and compares it with a reference value. The oscillator with frequency modulating function adjusts the switching frequency based on feedback signals, thereby regulating EMI noise while maintaining stable overcurrent protection levels through dynamic compensation of AC input voltage fluctuations.
Solution Approach 2:
The patent changes the operating parameters of the system by using an oscillator that can modulate switching frequency. This allows the system to adapt the switching frequency dynamically to reduce EMI noise while the overcurrent protection circuit maintains stable protection levels by compensating for AC input voltage changes through parameter adjustment.
2Reliability
If higher current ratings are specified for switches and transformers to handle voltage fluctuations, then overcurrent protection is improved, but device size and cost increase
Solution Approach 1:
The patent implements dynamic overcurrent protection where the protection level is not fixed but adapts to AC input voltage fluctuations in real-time. The overcurrent protection circuit dynamically adjusts its reference values and comparison thresholds based on detected voltage changes, allowing the system to maintain reliable protection with appropriately sized components rather than requiring oversized components for worst-case scenarios.
Solution Approach 2:
The patent changes the operational parameters of the switching element and transformer by implementing voltage-fluctuation-compensated overcurrent protection. This allows the system to optimize component ratings based on actual operating conditions rather than designing for maximum possible current, thereby reducing device size and cost while maintaining adequate protection capability.
3Reliability
If circuit components are oversized to handle peak currents during voltage fluctuations, then protection reliability is improved, but manufacturing cost increases
Solution Approach 1:
The patent implements dynamic protection that adapts to varying operating conditions, allowing the use of optimally sized components rather than oversized components designed for worst-case scenarios. The control circuit dynamically adjusts protection thresholds and switching parameters to maintain reliable protection across different AC input voltages, enabling cost-effective component selection.
Solution Approach 2:
The patent employs parameter changes in the control circuit to compensate for AC input voltage fluctuations, allowing the system to maintain protection reliability with appropriately rated components. By dynamically adjusting protection reference values and switching frequency, the system avoids the need for expensive oversized components while ensuring reliable operation under all operating conditions.
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
This solution allows for effective regulation of overcurrent protection levels without increasing circuit complexity, reducing the need for unnecessary current ratings in switches and transformers, thereby decreasing the size and cost of the power supply device.
Implementation Method 1
a current detecting circuit, connected to the switching element, that converts the current of the switching element into a voltage signal
Implementation Method 2
a slope compensation circuit that generates a slope compensation signal increasing monotonically in proportion to an on-state period of the switching frequency
Implementation Method 3
A transformer T, and a switching element Q1 connected between a direct current input and ground via a sense resistor R5
Implementation Method 4
An AC input 1 is supplied via a transformer 2 and capacitor 3 configuring an input filter to a diode bridge 4, and rectified to a direct current input voltage
Data Source
AI summary
A switching power supply device control circuit and switching power supply can combat fluctuation due to the input voltage in the peak current of a switching element, even when using an oscillator. A control IC is connected to a switching element and to a current detecting resistor, and controls the switching element, the control IC being configured of an OCP comparator that detects an overcurrent with respect to a load, an overcurrent level setting circuit that corrects a fluctuation occurring in the peak current of the switching element in response to the output voltage from the AC input, an oscillator having a frequency modulating function whereby the switching frequency with respect to the switching element can be modulated, and a slope compensation circuit that generates a slope compensation signal increasing monotonically in proportion to the time from the start of each cycle of an oscillating signal of the oscillator.