Flyback Converter Pin Multiplexing for Over-Temperature Protection
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Solution Overview
Problem
Conventional flyback power converters require additional pins for over-temperature protection (OTP) and mode detection, which is costly and inefficient, as they typically have a limited number of pins available.
Innovation Solution
Incorporating a temperature-sensitive resistor between the auxiliary winding and the current sense pin, along with a comparator and enable switch, allows the control circuit to trigger OTP and detect operation modes without requiring an additional pin by using the current sense and voltage feedback signals during the power switch's OFF period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional pins are added to the control circuit for OTP and mode detection functions, then the functionality and reliability are improved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the current sense pin perform multiple functions: it continues to detect current for normal operation while also detecting temperature-related signals and mode information by coupling a temperature-sensitive resistor between the auxiliary winding and the current sense pin. This allows OTP and mode detection without requiring additional pins, resolving the contradiction between functionality and device complexity
Solution Approach 2:
The patent combines the temperature sensing function with the existing current sense pin by connecting the temperature-sensitive resistor in parallel with the current sense circuit. This merging of functions allows the control circuit to obtain both current information and temperature information through a single pin, reducing the total pin count while maintaining reliability
2Adaptability or versatility
If the control circuit uses a package with a higher number of pins to accommodate OTP and mode detection, then the functionality is improved, but the manufacturing cost increases
Solution Approach 1:
The current sense pin is designed to handle multiple tasks including current detection, temperature sensing via the temperature-sensitive resistor, and mode detection. This multi-functionality allows the control circuit to achieve OTP and mode detection capabilities without requiring a higher-pin package, thereby reducing manufacturing costs while maintaining versatility
3Device complexity
If the control circuit uses the existing current sense pin for temperature detection, then the device complexity is reduced, but the measurement precision may be affected
Solution Approach 1:
The patent introduces a temperature-sensitive resistor as an intermediary element that converts temperature changes into resistance changes, which then modulate the signal on the current sense pin. This intermediary allows the control circuit to distinguish temperature-related signals from current signals, maintaining measurement precision while using the existing pin for both purposes
Solution Approach 2:
The temperature-sensitive resistor changes its resistance parameter in response to temperature variations, creating a detectable signal modulation on the current sense pin. The control circuit detects these parameter changes to determine temperature conditions and trigger OTP when necessary, achieving accurate temperature detection without additional pins
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
Enables effective over-temperature protection and mode detection within the existing pin constraints, reducing costs and improving operational efficiency by utilizing the existing pins for these critical functions.
Implementation Method 1
a temperature-sensitive resistor coupled between the auxiliary winding and the current sense pin, for providing a temperature-related signal to the control circuit
Implementation Method 2
a transformer having a primary winding for receiving an input voltage, a secondary winding for generating an output voltage, and an auxiliary winding
Data Source
AI summary
A flyback power converter includes a transformer which has a primary winding, a secondary winding, and an auxiliary winding; a power switch controlling the conduction of the primary winding; and a control circuit generating a control signal to control the power switch, wherein the control circuit is an integrated circuit having a current sensing pin for obtaining a current sensing signal of a current through the power switch. The flyback power converter further includes a temperature-sensitive resistor or a mode detection resistor coupled between the auxiliary winding and the current sensing pin. The temperature-sensitive resistor provides a temperature-related signal for the control circuit to perform an over-temperature protection, or the temperature-sensitive resistor provides a mode detection signal for the control circuit to determine an operation mode of the flyback power converter.