Auxiliary Winding Current Detection in Power Converters
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Solution Overview
Problem
Conventional methods for detecting output current in LLC circuits, especially in low-voltage high-current applications, face challenges such as high power loss, large volume, and inaccurate detection due to the use of current sensing resistors or transformers.
Innovation Solution
A current detecting circuit utilizing a transformer with an auxiliary winding and an impeder in parallel to the secondary winding, where the turns of the auxiliary winding match those of the secondary winding, allowing for accurate detection with minimal loss and reduced volume by leveraging the transformer's magnetic core for power transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensing resistor is used to detect output current, then the current detection is simple to implement, but large power loss and large volume are generated
Solution Approach 1:
The patent introduces an auxiliary winding as an intermediary element that couples the primary and secondary sides through magnetic coupling. This mediator allows current information to be transmitted from the secondary side to the primary side without direct electrical connection, thereby avoiding the need for a current sensing resistor on the output side and eliminating the associated power loss and volume issues.
Solution Approach 2:
The patent replaces the electrical measurement system (current sensing resistor) with a magnetic coupling system (auxiliary winding). By using electromagnetic induction, the current information is transferred through magnetic fields rather than direct electrical contact, which eliminates the I²R losses inherent in resistive sensing methods.
2Loss of energy
If a current transformer is used to detect load current, then small power loss is generated, but the volume and power density are affected by the magnetic component
Solution Approach 1:
The patent merges the current detection function with the existing transformer structure by adding an auxiliary winding to the transformer. This integration allows the detection function to be achieved without adding separate magnetic components, thereby maintaining high power density and minimizing volume increase while still achieving accurate current detection with minimal power loss.
Solution Approach 2:
The auxiliary winding serves multiple functions: it enables current detection, maintains magnetic coupling between primary and secondary sides, and integrates with the existing transformer structure. This multi-functionality allows the system to achieve detection capabilities without sacrificing power density or requiring additional dedicated magnetic components.
3Loss of energy
If the resistance of current sensing resistor is reduced to reduce power loss, then power loss decreases, but current sampling accuracy is affected
Solution Approach 1:
The auxiliary winding acts as an intermediary that transfers current information through magnetic coupling rather than requiring a low-value resistor. This mediator enables accurate current measurement without the trade-off between resistance value and power loss, as the measurement is performed through induced voltage in the auxiliary winding which is proportional to the primary current.
4Measurement precision
If a detection circuit is electrically connected in parallel to an inductor, then current detection is achieved, but the method is only applicable to power conversion circuits that include inductors
Solution Approach 1:
The auxiliary winding detection method is universally applicable to various power conversion circuits including LLC resonant converters, flyback converters, and forward converters. By coupling the auxiliary winding to the primary side, the detection method works with different circuit topologies and inductor configurations, providing broad adaptability across power conversion applications.
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 accurate detection of output current with almost no loss and small volume, saving space and reducing power converter losses compared to conventional methods.
Implementation Method 1
a primary winding, a secondary winding, and an auxiliary winding. The auxiliary winding is coupled to the secondary winding... The primary winding and the secondary winding are coupled through the magnetic core
Implementation Method 2
The primary winding and the secondary winding are coupled through the magnetic core
Data Source
AI summary
The present disclosure discloses a current detecting circuit of a power converter, which includes a transformer including: a magnetic core, a primary winding and a secondary winding, the primary winding and the secondary winding being coupled through the magnetic core, and a combination of the primary winding, the secondary winding and the magnetic core being used to transmit a main power of the power converter, the current detecting circuit includes: an auxiliary winding coupled to the secondary winding, the auxiliary winding and the secondary winding having the same number of turns and their dotted terminals being connected; and an impeder, one end thereof being coupled to the auxiliary winding to form a series branch, which is coupled in parallel to the secondary winding, and a terminal voltage of the impeder after being filtered being proportional to a magnitude of an output current of the power converter.