Step-down DC-DC Converter Noise Reduction via Coupled Coils
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Solution Overview
Problem
Conventional step-down switching DC-DC converters generate severe noise due to pulse and triangle wave currents, which cannot be completely eliminated, making them unsuitable for applications requiring low noise, especially in interplanetary probes using solar cells as power sources.
Innovation Solution
The proposed step-down switching DC-DC converter incorporates a configuration with input and output coils, intermediate capacitors, and coils that are electromagnetically coupled, allowing for complementary switching to convert ripple currents into triangle waves or eliminate them, thereby reducing noise and enabling miniaturization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional switching DC-DC converter uses pulse wave current through the switch, then voltage conversion efficiency is maintained, but severe switching noise and harmonic noise are generated
Solution Approach 1:
The patent divides the conventional single-coil structure into multiple coils (first coil L1, second coil L2, third coil L3, fourth coil L4) with specific connections. This segmentation allows the current waveform to be transformed from a pulse wave to a triangle wave, reducing switching noise while maintaining voltage conversion efficiency.
Solution Approach 2:
The patent employs periodic switching of the switch S at frequency f, creating a controlled triangle wave current through the coils. This periodic action transforms the harmful pulse wave into a less noisy triangle wave while maintaining the necessary voltage conversion function.
2Object-generated harmful factors
If ripple currents are reduced in conventional converters, then noise is slightly reduced, but ripple currents cannot be completely eliminated
Solution Approach 1:
The patent merges multiple coils (L1, L2, L3, L4) with specific turn ratios and connections to create a combined electromagnetic effect. This merging allows the triangle wave currents in different coils to interact in a way that eliminates ripple currents at the output, achieving complete ripple current elimination rather than just reduction.
3Object-generated harmful factors
If multiple coils and intermediate capacitors are added to reduce noise, then noise characteristics improve, but device complexity increases
Solution Approach 1:
The patent designs the circuit so that the same coils (L1, L2, L3, L4) perform multiple functions: voltage conversion, noise reduction through triangle wave generation, and ripple current elimination through their specific connections and turn ratios. The intermediate capacitors (C1, C2) also serve dual purposes in the circuit operation.
4Power
If conventional buck converter topology is used, then voltage step-down conversion is achieved, but severe noise from pulse wave and triangle wave currents prevents use in low-noise applications
Solution Approach 1:
The patent introduces asymmetry in the coil connections and turn ratios (n1, n2, n3, n4) to transform the symmetric pulse wave current into an asymmetric triangle wave current pattern. This asymmetric configuration, with specific connection points a, b, c, d, enables noise reduction while maintaining the voltage step-down conversion function.
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 configuration effectively reduces noise, allows for miniaturization of the converter, and integrates coils into a single transformer, achieving low noise and efficient voltage conversion.
Implementation Method 1
the input coil and the first intermediate coil that are electromagnetically coupled with each other, and the output coil and the second intermediate coil are electromagnetically coupled with each other
Data Source
AI summary
A step-down switching DC-DC converter may include an input coil on the input side, an output coil on the output side, a switch, an output capacitor, a first series circuit connected between a connection point on which the input coil and the switch are connected each other and a negative pole of a power source, and a second series circuit connected between a connection point on which the output coil and the switch are connected to each other and the negative pole of the power source. A connection point between a first intermediate capacitor and the first intermediate coil is connected to a connection point between a second intermediate capacitor and the switch via a switching device cooperating with the switch. The input coil and the first intermediate coil are electromagnetically coupled with each other. The output coil and the second intermediate coil are electromagnetically coupled with each other.