Multiplex Pin Sensing Circuit for Accurate Thermal and Brown-Out Protection
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Solution Overview
Problem
Existing power conversion systems suffer from inaccurate over-temperature and brown-out protection due to the use of diodes in external temperature sensing circuits, which affect the accuracy of temperature sensing and protection operations.
Innovation Solution
A power conversion system with a multiplex pin and a conversion control circuit that includes a sensing circuit with a temperature-sensitive element, a current source, and a bias switch, allowing for accurate temperature and input voltage sensing by generating multiplexed sensing signals during different protection periods, without the need for diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a diode is used in the external temperature sensing circuit, then the circuit can be simplified, but the temperature sensing accuracy deteriorates due to reverse leakage current and forward bias changes
Solution Approach 1:
The patent extracts the temperature sensing function from the external circuit into the control circuit itself. The sensing pin is integrated within the control circuit, eliminating the need for external diodes and resistors. This extraction removes the source of measurement error (diode reverse leakage current) while maintaining the temperature sensing capability through an internal current source that provides stable bias current regardless of temperature variations.
Solution Approach 2:
The patent introduces an internal current source as an intermediary element within the control circuit. This current source provides a stable bias current to the sensing pin, acting as a mediator that eliminates the need for external passive components (diodes and resistors) that caused measurement errors. The current source ensures accurate temperature sensing by maintaining constant current flow independent of temperature-induced parameter changes in external components.
2Reliability
If a separate temperature sensing circuit with diode and resistor is used, then temperature protection can be implemented, but the brown-out protection accuracy deteriorates due to shared pin usage
Solution Approach 1:
The patent implements periodic action by sequentially activating different protection functions through timing control. The control circuit alternates between temperature sensing mode and brown-out protection mode in different time periods. During specific time windows, the sensing pin measures temperature; during other windows, it measures input voltage. This time-division multiplexing allows both protection functions to share the same pin without mutual interference, maintaining accuracy for both measurements.
3Device complexity
If external passive components are used for temperature sensing, then the control circuit can remain simple, but the overall system accuracy deteriorates due to component tolerances and temperature coefficients
Solution Approach 1:
The patent merges the temperature sensing function with the control circuit itself. The sensing pin, current source, and comparison logic are all integrated within the control circuit chip. This consolidation eliminates external passive components (diodes and resistors) that introduced accuracy errors due to their tolerances and temperature coefficients. By combining these functions internally, the system achieves higher measurement precision without significantly increasing control circuit complexity.
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
Enhances the accuracy of over-temperature and brown-out protection operations by eliminating the non-ideal effects of diodes, ensuring precise temperature detection and voltage sensing.
Implementation Method 1
a sensing circuit, including a temperature-sensitive element, wherein the sensing circuit is coupled to the AC input voltage or the rectified voltage and configured to generate a multiplexed sensing signal
Implementation Method 2
a current source and a bias switch, serially coupled to the multiplex pin; wherein during the over temperature protection period, the bias switch is conductive to control the current source to provide a bias current to the sensing circuit through the multiplex pin
Data Source
AI summary
A power conversion system includes: a rectifier for rectifying an AC input voltage to generate a rectified voltage; a power stage circuit coupled to the rectifier; a sensing circuit coupled between a multiplex pin and either the AC input voltage or the rectified voltage and configured to generate a multiplexed sensing signal; and a control circuit for performing operations for over-temperature protection and brown-out protection during respective over-temperature and brown-out protection periods based on the status of the multiplexed sensing signal. The control circuit includes: the multiplex pin; and a current source and a bias switch, serially coupled to the multiplex pin. During the over-temperature protection period, the bias switch is conductive to provide a bias current to the sensing circuit to generate a temperature sensing signal. Outside the over-temperature protection period, the bias switch is non-conductive to stop providing the bias current, thereby generating an input voltage sensing signal.