SMPS Controller Pin Multiplexing for Thermal Fault Signaling
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Solution Overview
Problem
Existing controllers for switched mode power supplies require multiple pins for temperature sensing and fault signal transmission, which increases the complexity and cost of the secondary side circuitry and may lead to reduced power density and increased risk of overheating.
Innovation Solution
A single pin (STOP pin) is used for both temperature sensing and fault signal transmission, connecting a thermistor and an optocoupler LED in parallel, with a reference-source providing a temperature-measurement-signal and an OTP-comparator comparing it to a threshold-level to generate an OTP-signal, which controls a switchable-current-source to emit a light-signal indicative of a fault.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple pins are used for temperature sensing and fault signal transmission, then the functionality is complete, but the device complexity and pin count increase
Solution Approach 1:
The STOP pin is designed to perform multiple functions: it serves as the temperature sensing input during normal operation and as the fault signal transmission output when a fault occurs. The controller internally switches between these functions based on the OTP signal state, eliminating the need for separate dedicated pins for each function.
Solution Approach 2:
The patent combines the temperature sensing function and fault signal transmission function into a single pin (STOP pin). The thermistor and optocoupler LED share the same physical pin connection, and the controller multiplexes the pin's function based on operational state, reducing the total pin count while maintaining both functionalities.
2Productivity
If multiple pins are used for temperature sensing and fault signal transmission, then the functionality is complete, but the power density is reduced
Solution Approach 1:
The STOP pin serves dual purposes as both temperature sensing input and fault signal output, reducing the number of required pins and associated circuitry. This consolidation increases power density by reducing the physical space needed for secondary side components.
Solution Approach 2:
The patent merges the temperature sensing path and fault signal transmission path to share common components (STOP pin, voltage-supply-pin, thermistor, optocoupler LED), thereby reducing overall circuit complexity and increasing power density.
3Reliability
If multiple pins are used for temperature sensing and fault signal transmission, then the functionality is complete, but the risk of overheating increases
Solution Approach 1:
The STOP pin functions as both temperature monitoring input and fault alarm output. When over-temperature is detected via the thermistor, the controller activates the OTP signal which then drives the optocoupler LED through the same STOP pin, providing reliable fault protection while simplifying the controller design.
Solution Approach 2:
The system implements feedback through the OTP comparator which continuously monitors the temperature measurement signal and compares it against a threshold. When the threshold is exceeded, the feedback loop activates the switchable-current-source to drive the optocoupler LED, creating a reliable automatic protection mechanism.
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 reduces the number of pins required, simplifying the secondary side controller, enhancing power density, and effectively communicating fault conditions to the primary side while maintaining reliable temperature monitoring and fault protection.
Implementation Method 1
a thermistor and an LED of an optocoupler are connected in parallel with each other between the voltage-supply-pin and the STOP pin... the STOP pin is configured to receive a temperature-measurement-signal from the thermistor
Implementation Method 2
an LED of an optocoupler... the bias-current is configured to cause the LED to emit a light-signal that is representative of a fault
Data Source
Figure 1
Figure 2~5
Figure 3~4
AI summary
A controller (202) for a secondary side (103) of a switched mode power supply (100). A thermistor (222) and an LED (224) of an optocoupler are connected in parallel with each other between a voltage-supply-pin (206) and a STOP pin (204) of the controller (202). A reference-source (208) provides a reference-signal between the STOP pin (204) and the voltage-supply-pin (206). The STOP pin (204) receives a temperature-measurement-signal from the thermistor (222), wherein the temperature-measurement-signal is representative of the resistance of the thermistor (222). The controller (202) also includes an OTP-comparator (210) that compares: (i) the temperature-measurement-signal; with (ii) a threshold-level, and provides an OTP-signal (226) that is representative of whether or not the temperature-measurement-signal at the STOP pin (204) crosses the threshold-level; and a switchable-current-source (218) that selectively provides a bias-current to the STOP pin (204) based on the OTP-signal (226), wherein the bias-current causes the LED (224) to emit a light-signal that is representative of a fault to an associated photo-detector (976).