Flyback Power Supply Current Sense Transformer Heat Reduction
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Solution Overview
Problem
Power supplies with flyback topology face challenges due to the high current and heat dissipation issues in current sensing resistors, which are typically large and costly, as they are in series with the secondary winding of the flyback transformer.
Innovation Solution
Incorporating a current sense transformer coupled to the flyback transformer to generate a current signal indicative of the power supply's output current, allowing for current measurement without the need for a current sensing resistor in series with the secondary winding, thereby reducing heat dissipation and size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensing resistor is used in series with the secondary winding to sense output current, then current measurement is achieved, but the resistor dissipates large amounts of heat and requires large physical size
Solution Approach 1:
The patent introduces a current sensing transformer as an intermediary device to measure the output current. The transformer couples to the secondary winding and provides a scaled-down version of the current signal through its secondary winding, allowing accurate current measurement without placing a high-power resistor in the main current path. This mediator approach enables measurement while avoiding the heat dissipation problem.
Solution Approach 2:
The patent replaces the traditional resistive current sensing method with a transformer-based electromagnetic sensing method. Instead of using Ohm's law (V=IR) with a physical resistor that dissipates power, the system uses electromagnetic induction through the current sensing transformer to obtain the current signal, thereby eliminating the need for power-dissipating resistive elements.
2Measurement precision
If a current sensing resistor is used in series with the secondary winding, then current measurement is achieved, but the resistor becomes physically large and costly
Solution Approach 1:
The current sensing transformer acts as an intermediary that provides current measurement capability without requiring a large physical resistor. The transformer's magnetic coupling allows the sensing function to be performed with a much smaller component that does not need to physically withstand the full current load.
Solution Approach 2:
The patent substitutes the mechanical/resistive sensing approach with an electromagnetic field-based approach. The current sensing transformer uses magnetic flux to sense current, replacing the need for a large physical resistor and enabling compact design.
3Measurement precision
If a current sensing resistor is used in series with the secondary winding, then current measurement is achieved, but the overall device complexity and cost increase
Solution Approach 1:
The current sensing transformer serves multiple functions: it provides current measurement, electrical isolation between primary and secondary sides, and signal scaling. This multi-functionality reduces the need for additional components and simplifies the overall circuit design compared to using a power-rated resistor for sensing.
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 enables efficient current measurement and control in power supplies, reducing the need for large and costly current sensing resistors and minimizing heat dissipation, while maintaining accurate output regulation.
Implementation Method 1
The current sense transformer is used to generate a current signal indicative of a current output by the power supply
Data Source
AI summary
A power supply having a flyback topology includes a flyback transformer and a current sense circuit that outputs a current signal indicative of a current output by the power supply. The current sense circuit includes a current sense transformer coupled to the flyback transformer.