Switching Power Supply Current Limiting Feedback Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing switching power supply devices lack a current limiting function, particularly when a load current increases, and are vulnerable to damage from short-circuits due to insufficient current limiting, with operation characteristics affected by variations in transistor thresholds and requiring an unnecessary second auxiliary winding for optocoupler current.
Innovation Solution
A switching power supply device with a current limiting feedback circuit using inverse proportion feedback currents and an on/off control system independent of transistor thresholds, eliminating the need for a second auxiliary winding and allowing for adjustable current limiting characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second auxiliary winding is added to obtain optocoupler current, then the optocoupler can operate reliably, but the device complexity and number of components increase
Solution Approach 1:
The single auxiliary winding is designed to serve multiple functions: it provides current for the optocoupler during normal operation and generates feedback current during current limiting operation. This multi-functional design eliminates the need for a separate second auxiliary winding while maintaining reliable optocoupler operation.
Solution Approach 2:
The patent utilizes different operational parameters (voltage levels, current directions) from the single auxiliary winding to achieve different functions. By detecting voltage polarity changes and current flow directions, the system distinguishes between normal operation mode and current limiting mode, allowing one winding to provide multiple operational modes.
2Measurement precision
If conventional current limiting is implemented using sense resistors and transistors, then current detection is possible, but the current limiting characteristics are affected by transistor threshold variations
Solution Approach 1:
The patent implements a feedback mechanism where the auxiliary winding generates feedback current that is fed back to the control circuit. This feedback current directly reflects the primary winding current status, creating a closed-loop control system that automatically adjusts the switching transistor duty cycle to limit current, eliminating dependence on transistor threshold characteristics.
Solution Approach 2:
The patent replaces the conventional transistor-based current limiting mechanism (which relies on transistor threshold voltages) with an electromagnetic induction-based feedback mechanism. The auxiliary winding induces voltage proportional to the rate of change of primary current, providing a more stable and predictable current limiting characteristic independent of transistor parameters.
3Device complexity
If no current limiting function is provided, then the device structure remains simple, but the device is vulnerable to damage from short-circuits and overcurrent conditions
Solution Approach 1:
The system uses the auxiliary winding to automatically generate feedback current that reflects the primary winding current status. This self-service mechanism allows the power supply to automatically detect and limit overcurrent conditions without requiring external protection circuits, maintaining structural simplicity while providing reliable protection.
Solution Approach 2:
The patent implements preliminary protection by continuously monitoring the primary winding current through the auxiliary winding and preemptively limiting the current before damage can occur. The feedback mechanism acts in advance to prevent short-circuit damage by reducing the duty cycle when overcurrent is detected, rather than reacting after damage has occurred.
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
The solution provides effective current limiting and protection against overcurrent, allowing for flexible operation characteristics and preventing device damage from short-circuits, while ensuring reliable on/off timing independent of transistor threshold variations.
Implementation Method 1
when a current starts flowing through the primary winding L11 to which the switching transistor MN11 is connected due to the DC voltage Vin, an induced electromotive force is generated from each of the windings L12, L13, and L14 of the transformer 60
Implementation Method 2
When the switching transistor MN11 turns off such that a current flowing through the primary winding L11 is interrupted, a flyback voltage is generated from each of the windings L11 to L14
Data Source
AI summary
A switching power supply device includes a switching transistor, a sense resistor, a transformer, an optocoupler, and a current limiting feedback circuit. The switching transistor is controlled to be turned on and turned off. The sense resistor is configured to generate a sense voltage when the switching transistor is turned-on. The transformer includes a primary winding to which an input voltage is applied when the switching transistor is turned-on, a secondary winding is configured to supply an output voltage to a load, and an auxiliary winding that is configured to detect the output voltage. The optocoupler is configured to generate first and second optocoupler currents corresponding to the output voltage. The current limiting feedback circuit is configured to generate first, second, and third feedback currents using a voltage of the auxiliary winding, the first, second, and third feedback currents being in inverse proportion to the output voltage.