Control Ringing in Switching Converters with Ferrite Beads

Ringing or buzzing in electronic components and within circuits is common, and engineers must calculate the effects and employ some type of control to mitigate any problems. Within power semiconductors, this unwanted oscillation occurs when the switch turns on and off in the vicinity of parasitic inductance and capacitance. The electromagnetic interference (EMI) is often in the range of 50MHz to 200MHz, and this essentially turns PCB traces and component leads into functional antennas—introducing conducted and radiated noise into the circuit.

Parasitic Element Definition: “Any circuit element or property present within a component or group of components that has a negative effect on the performance of the circuit.” Ringing is an example.

Proper placement of ferrite beads may provide effective control of ringing in power converter circuits. They use relatively little PCB space compared to other solutions, do not compromise power efficiency, and offer low resistance at low frequencies, but high resistance in the 10MHz to 1GHz or higher range which includes the 50MHz to 200MHz range often associated with board level EMI. Other solutions such as L-C filters and filter capacitors are not effective in that range and provide very little attenuation of noise in this type of circuit.

Wurth Electronik offers a detailed guide to selecting and placing ferrite beads to control ringing in switching converters. The LTC3703 synchronous controller IC on the DC501A evaluation board is used as an example circuit, and a full study of oscillation measurements and circuit calculations are given. Links to related products on the Digi-key site are shown below.

Wurth Electronik Application Note ANP025 [click here ].

DC501A demo board for LTC3703 (Digi-key part number DC501A) [click here ]. Product Index > Development Boards, Kits, Programmers > Evaluation Boards – DC/DC & AC/DC (Off-Line) SMPS > Analog Devices Inc. DC501A

LTC3703 Switching Controllers [click here ]. Product Index > Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Controllers > LTC3703


Interested in testing circuits as shown in the Wurth Elektronik App Note? Check out the Digi-key selection of oscilloscopes: [click here ]. Product Index > Test and Measurement > Equipment - Oscilloscopes


Find a large selection of Wurth Elektronik ferrite products in the following link: [click here ]. Product Index > Filters > Ferrite Beads and Chips > Wurth Elektronik

There are also many more ferrite bead and chip manufacturers on the Digi-key site: [click here ]. Product Index > Filters > Ferrite Beads and Chips

Find those and many more electronic components from the Digi-key home page: [click here ].

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