Switching Power Supply Overcurrent Detection via Dynamic Reference Voltage
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Solution Overview
Problem
Existing power supply systems face a limitation in achieving a wide selection range of reference voltages for overcurrent detection across different modes, due to voltage tolerance constraints in power supply control ICs, which narrows the selection range when switching between normal and low load modes.
Innovation Solution
A power supply system with a switching power supply and a control unit that includes a transformer, semiconductor switch, rectifier/smoothing circuit, and overcurrent detection circuit, where the overcurrent detection circuit is configured to generate different reference voltages for normal and low output modes, allowing for wider voltage selection and effective overcurrent detection without being limited by the control IC's tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the supply voltage VCC is increased to expand the reference voltage selection range for overcurrent detection, then the selection range of reference voltages is improved, but the power supply control IC cannot withstand voltages higher than its tolerance (20V)
Solution Approach 1:
The patent introduces a voltage dividing circuit as an intermediary between the high-voltage induced voltage from the transformer and the power supply control IC. This dividing circuit steps down the high voltage to a level within the IC's tolerance (20V), allowing the system to operate with high output voltages (up to 72V in normal mode) while protecting the IC from damage. This enables the reference voltage selection range to be determined by the voltage dividing ratio rather than being limited by the IC's voltage tolerance.
2Reliability
If a step-down circuit is connected between the primary auxiliary winding and the power supply control IC to reduce voltage below tolerance, then the IC is protected from overvoltage, but the selection range of threshold voltage for overcurrent detection is narrowed
Solution Approach 1:
The patent implements dynamic reference voltage selection by providing multiple reference voltage generation circuits that can be switched between different modes. In normal output mode, a first reference voltage is used, while in low output mode, a second reference voltage is used. This dynamic switching allows the overcurrent detection threshold to be appropriately adjusted for each operating mode, expanding the effective selection range beyond what a fixed step-down circuit would allow.
Solution Approach 2:
The patent changes the reference voltage parameter based on operating conditions. By switching between different reference voltage values (first reference voltage for normal mode, second reference voltage for low load mode), the system adapts the overcurrent detection threshold to match the actual operating requirements, thereby expanding the functional selection range while maintaining IC protection.
3Measurement precision
If the threshold voltage for overcurrent detection is increased proportionally with output voltage to maintain detection accuracy, then detection accuracy is improved, but the voltage range required exceeds the control IC's tolerance
Solution Approach 1:
The patent segments the voltage measurement and comparison functions into separate domains. The voltage dividing circuit handles the high-voltage side by stepping down the induced voltage to a safe level for the IC. Meanwhile, the reference voltage generation circuits generate appropriate reference voltages for each operating mode. This segmentation allows accurate overcurrent detection to be achieved in the low-voltage domain (within IC tolerance) while still monitoring high-voltage conditions accurately through proportional relationships maintained by the circuit design.
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 system effectively adjusts output current and voltage according to load size, restricting high current flow in low output mode and enabling wider reference voltage range settings, enhancing overcurrent detection flexibility and accuracy.
Implementation Method 1
The transformer is configured to induce a voltage in a secondary side by oscillation of a primary side
Data Source
AI summary
A power supply system includes a switching power supply. The switching power supply includes an overcurrent detection circuit. The overcurrent detection circuit includes a current detecting resistor, a reference voltage generation circuit, and a comparison circuit. The current detecting resistor is provided on a secondary side of a transformer. The reference voltage generation circuit generates a first reference voltage when an output voltage of the switching power supply is a first output voltage and a second reference voltage lower than the first reference voltage when the output voltage is a second output voltage. The comparison circuit detects an overcurrent by comparing a voltage across the current detecting resistor with the first reference voltage or the second reference voltage.