DC/DC Converter Ringing Frequency Control for EMI Reduction
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Solution Overview
Problem
Conventional DC/DC converters using switching circuits face efficiency deterioration and insufficient Electromagnetic Interference (EMI) reduction due to ringing frequency components, which are not effectively addressed by existing techniques such as diode insertion, snubber circuits, or low-pass filter circuits.
Innovation Solution
A DC/DC converter with a ringing frequency changing circuit that includes a capacitor and a control circuit to selectively change the ringing frequency only when it affects EMI, connected between the drain and source of the switching FET, and controlled to be valid only during specific switching events, minimizing efficiency loss and EMI radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a switching method is used in the power supply circuit to convert voltage, then efficiency is improved, but voltage fluctuation (ringing) occurs at on/off switching moments causing EMI
Solution Approach 1:
The patent changes the ringing frequency parameter by inserting a capacitor between the drain and source of the switching FET. This capacitor modifies the resonant frequency of the parasitic inductance and capacitance in the circuit, shifting the ringing frequency away from the printed board's resonance frequency to reduce EMI radiation while maintaining the switching operation for efficiency.
Solution Approach 2:
The patent introduces a capacitor as an intermediary component between the switching FET's drain and source. This capacitor acts as a mediator that alters the electrical characteristics of the switching node, specifically changing the ringing frequency without preventing the switching action itself, thus reducing EMI while preserving power supply efficiency.
2Object-generated harmful factors
If snubber circuits are provided at both ends of an inductor to reduce ringing, then ringing is reduced, but the efficiency of the power supply is worsened because snubber circuits always operate
Solution Approach 1:
The patent avoids the efficiency penalty of always-operating snubber circuits by using a capacitor to change the ringing frequency parameter instead. This approach reduces EMI by frequency shifting without the continuous energy dissipation associated with resistive snubber circuits, thereby maintaining power supply efficiency.
3Object-generated harmful factors
If the ringing frequency is lowered to be below the resonance frequency of the printed board, then EMI radiation is reduced, but additional components like snubber resistors or diodes are typically required
Solution Approach 1:
The patent achieves EMI reduction by lowering the ringing frequency using a capacitor that serves multiple functions: it modifies the resonant frequency of the switching node, filters high-frequency noise, and works in conjunction with existing circuit components. This multi-functional approach reduces EMI without requiring additional specialized components like snubber resistors or diodes.
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
The solution effectively reduces EMI levels by altering the ringing frequency to be lower than the resonance frequency of the printed board, thereby minimizing efficiency deterioration and eliminating EMI radiation, without the need for additional components like snubber resistors or diodes.
Implementation Method 1
the ringing frequency itself which worsens EMI cannot be changed by the diode... the ringing frequency changing circuit... effectively reduces EMI levels by altering the ringing frequency to be lower than the resonance frequency of the printed board
Implementation Method 2
a switching circuit for driving a switching FET for increasing or decreasing voltage... When a switching method is used at the time of converting voltage in the power supply circuit (DC/DC converter circuit)
Implementation Method 3
One end of a capacitor is connected to a drain of the switching FET... the capacitor is connected between the drain and the source of the switching FET
Data Source
AI summary
The present invention is directed to sufficiently reduce the level of EMI which occurs from a switching FET in a DC/DC converter and minimize deterioration in efficiency of a power supply. A DC/DC converter includes a switching circuit for driving a switching FET for increasing or decreasing voltage, and a switching circuit for driving a ringing frequency changing circuit. One end of a capacitor is connected to a drain of the switching FET for increasing or decreasing voltage, and the other end of the capacitor is connected to a drain of an FET for the ringing frequency changing circuit. A source of the FET for the ringing frequency changing circuit is connected to GND, and a control circuit is provided which makes the ringing frequency changing circuit valid so that a ringing frequency becomes low only in a ringing frequency component exerting large influence on deterioration in EMI.