Over-voltage Comparator Shutdown Circuit for Flyback Power Supplies
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Solution Overview
Problem
Existing power supplies for high integrity electronic control circuits, particularly in automated machinery and safety-critical systems, fail to predictably limit output voltages in fault conditions, making it difficult to correctly size protective measures like fuses and TVS diodes, especially in fly-back converters where voltage cannot be predicted.
Innovation Solution
The implementation of an over-voltage comparator and shutdown circuit that uses the sum of supply voltage and output voltage reflected back to the primary winding as a signal to monitor and limit output voltages, ensuring the power supply shuts down when pre-determined limits are exceeded, thereby preventing excessive voltage and allowing for proper sizing of protective components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prior art power supplies are used without voltage monitoring, then the power supply can operate continuously, but the output voltage cannot be predicted in fault conditions and may exceed safe limits
Solution Approach 1:
The patent implements preliminary action by monitoring the voltage at the primary winding terminal before it can rise to dangerous levels. The shutdown circuit is pre-configured with a reference voltage that corresponds to a predetermined maximum output voltage. When the monitored voltage approaches the unsafe threshold, the circuit proactively shuts down the power supply before a fault condition can develop, thereby ensuring predictable voltage behavior without requiring complex post-fault analysis.
Solution Approach 2:
The patent uses an intermediary approach by monitoring the voltage at the primary winding terminal (VSENSE) rather than directly monitoring the output voltage. This intermediary measurement point provides indirect but reliable information about the output voltage state through the transformer turns ratio relationship. The VSENSE voltage serves as a mediator that allows the shutdown circuit to infer output voltage conditions and trigger protection without direct contact with the high-voltage output side, simplifying the overall system architecture.
2Reliability
If the power supply shuts down immediately upon detecting over-voltage, then safety is improved, but the loss of power supply operation increases
Solution Approach 1:
The patent applies preliminary anti-action by preventing the harmful effect of over-voltage before it can occur. The shutdown circuit continuously monitors the VSENSE voltage and is pre-thresholded to trigger shutdown at a voltage level that corresponds to the predetermined maximum output voltage. This preemptive shutdown mechanism ensures that the output voltage never exceeds the safe limit, thereby maintaining safety integrity level compliance while avoiding unnecessary shutdowns during normal operation.
Solution Approach 2:
The patent uses parameter changes by establishing a predetermined maximum output voltage threshold that corresponds to a specific VSENSE voltage level. The shutdown circuit compares the real-time VSENSE voltage against this predetermined reference threshold. When the VSENSE voltage exceeds the reference level, indicating that the output voltage has reached the maximum safe limit, the circuit changes its operational state by activating the shutdown signal. This parameter-based control ensures predictable shutdown behavior while maintaining continuous operation within safe parameters.
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 effectively limits output voltages in fault conditions, ensuring the power supply operates within safe parameters, allowing for correct sizing of protective measures and meeting stringent safety integrity levels, such as SIL3 and category 4 performance requirements.
Implementation Method 1
a first voltage divider connected between ground and a monitored voltage, the voltage divider including a first resistor and a second resistor
Implementation Method 2
a first threshold comparator, a monitored input of the first threshold comparator connected between the first resistor and the second resistor
Implementation Method 3
a cathode of the first threshold comparator connected to the switch mode regulator
Data Source
AI summary
An over-voltage comparator and shutdown circuit for a power converter, comprising at least a first voltage divider connected between ground and a monitored voltage, the voltage divider including a first resistor and a second resistor, a switch mode regulator connected to a primary switch of the power converter, and a first threshold comparator, wherein a monitored input of the first threshold comparator is connected between the first resistor and the second resistor, an anode of the first threshold comparator is connected to ground, and a cathode of the first threshold comparator is connected to the switch mode regulator, and wherein the monitored voltage is voltage at an end of a primary winding of the power converter. An auxiliary output circuit of the power converter may be provided having a first output providing the monitored voltage and a second output providing power to the switch mode regulator.