Switching Power Supply Feedback Loop Protection Circuit
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Solution Overview
Problem
Switching power supplies face challenges in effectively protecting against malfunctioning feedback loops, particularly in identifying excessively high output voltages, which can lead to catastrophic failures due to the need for precise and safe monitoring across insulation barriers without increasing component count or power consumption.
Innovation Solution
A circuit that generates a voltage proportional to the output voltage, uses a comparator to compare this voltage with a reference, and employs a counter to indicate malfunctioning by exceeding a preset number of threshold crossings, providing protection without relying on load conditions and minimizing external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of output voltage is implemented, then measurement precision is improved, but device complexity increases due to additional insulation barriers and components
Solution Approach 1:
The patent uses an auxiliary winding on the transformer as an intermediary to indirectly measure the output voltage. This winding is magnetically coupled to the primary side, allowing voltage information to be transferred across the insulation barrier without direct electrical contact. The auxiliary voltage is then rectified and filtered to provide a proportional DC voltage that represents the output voltage, achieving accurate measurement while maintaining galvanic isolation.
Solution Approach 2:
The patent creates a copy of the output voltage signal through the auxiliary winding transformation. By using the transformer ratio, a scaled-down version of the output voltage is obtained on the primary side, which can be safely measured and processed. This copied signal is sufficient for protection purposes without requiring direct access to the high voltage output.
2Reliability
If traditional OVP circuits are used, then over-voltage protection is provided, but power consumption increases and external components are required
Solution Approach 1:
The patent combines the over-voltage protection function with the existing feedback loop components. The same auxiliary winding used for feedback also provides the voltage for OVP detection. The protection circuit shares the rectifier diode and filter capacitor with the feedback circuitry, eliminating the need for separate power-consuming components and reducing overall power consumption while maintaining reliable protection.
Solution Approach 2:
The auxiliary winding serves multiple functions: it provides feedback voltage for the control loop, supplies power to the control circuitry, and enables over-voltage protection detection. This multi-functionality reduces the number of dedicated components needed for protection, lowering both component count and associated power consumption.
3Measurement precision
If resistance deterioration monitoring is implemented, then detection precision is improved, but response time worsens due to slow voltage drift
Solution Approach 1:
The patent establishes a predetermined threshold voltage level that represents the safe operating limit. The protection circuit continuously monitors the auxiliary voltage and is prepared to trigger immediately when this threshold is exceeded. By setting the threshold in advance and maintaining ready-state monitoring circuitry, the system can respond quickly to both gradual drifts and sudden over-voltage conditions without delay.
Solution Approach 2:
The patent implements a continuous feedback mechanism where the auxiliary voltage is constantly compared against the reference threshold. This real-time feedback allows the system to detect both slow resistance deterioration and sudden failures, triggering protection action as soon as the voltage exceeds the safe limit, thereby minimizing response time while maintaining detection precision.
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 offers precise and safe over-voltage protection with minimal additional consumption, immunity to external disturbances, and no need for additional pins or components, effectively preventing output voltage escalation in switching power supplies.
Implementation Method 1
generating a voltage proportional to the output voltage
Implementation Method 2
uses a comparator to compare this voltage with a reference
Data Source
AI summary
A method and the related circuit protect against malfunctioning of the feedback loop in switching power supplies. More particularly, the circuit identifies a condition of excessively high voltage at the output. In one embodiment the circuit for the protection against malfunctioning of the feedback loop of a switching power supply comprises: circuitry that generates a voltage proportional to the output voltage of the switching power supply; a comparator for comparing the voltage proportional to the output voltage with a reference voltage; a counter coupled to the comparator and capable of supplying an output signal when said voltage proportional to the output voltage exceeds said reference voltage a threshold number of times; said output signal is indicative of a malfunctioning of the feedback loop.