Switching Power Supply Peak Current Limiter Using Switching Period
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Solution Overview
Problem
Switching power supplies with quasi-resonant control circuits face challenges in maintaining consistent overcurrent protection across wide AC input voltage ranges, leading to potential stress on loads and heat generation due to fluctuations in DC input voltage, which existing solutions attempt to address by complicating input correction circuits.
Innovation Solution
A switching power supply design that utilizes the switching period of the switching element to calculate a current control threshold value for overcurrent protection, simplifying the configuration by focusing on the switching period rather than forward voltage, thereby reducing dependence on DC input voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the threshold current value for overcurrent protection is changed drastically according to the pulse-shaped forward voltage that is proportional to the DC input voltage, then the dependence of overcurrent protection on DC input voltage changes is reduced, but the device complexity increases due to requiring a relatively complicated input correction circuit
Solution Approach 1:
The patent changes the parameter used for threshold current value adjustment from forward voltage (which requires complex circuitry to detect and process) to switching period (which is already available from the quasi-resonant control operation). By detecting the switching period and using it to determine the threshold current value, the system achieves voltage compensation without adding complex forward voltage detection circuits.
Solution Approach 2:
The system uses its own switching period signal (already generated by the control circuit for quasi-resonant operation) to simultaneously control both the switching timing and the overcurrent protection threshold. This self-service approach eliminates the need for separate forward voltage sensing and processing circuits, reducing overall system complexity while maintaining protection reliability.
2Reliability
If the DC input voltage applied to the primary coil of the transformer becomes high, then the current that flows through the switching element becomes low, but the output power of the switching power supply increases causing extra stress on the load or excess heat generation in the transformer
Solution Approach 1:
The patent implements a feedback mechanism where the detected switching period is used to adjust the threshold current value dynamically. When the switching period indicates high input voltage conditions, the threshold is adjusted to prevent excessive output power, and vice versa. This closed-loop feedback ensures consistent output power and protects against harmful effects while maintaining switching element protection.
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 approach allows for reliable overcurrent protection and consistent output power across varying input voltages, reducing the complexity of the input correction circuit and preventing excessive stress on loads or transformer heat generation.
Implementation Method 1
the current that flows through the primary coil of the transformer induces a voltage in the secondary coil of the transformer
Data Source
AI summary
A switching power supply includes: a transformer having a primary coil and a secondary coil; a switching element that is connected in series to the primary coil of the transformer so as to turn a direct-current input voltage applied to the primary coil of the transformer ON and OFF; a rectifying and smoothing circuit that rectifies a voltage induced in the secondary coil of the transformer to generate a direct-current output voltage; and a control circuit that turns the switching element ON and OFF in accordance with the direct-current output voltage, wherein the control circuit includes an input correction circuit that detects a switching period of the switching element and limits a peak value of a current flowing through the switching element in accordance with the detected switching period.