Dan Chen

Reduction of power supply EMI emission by switching frequency modulation

Electromagnetic interference (EMI) emission is always of grave concern for power electronic circuit designers. Due to rapid switching of high current and high voltage, interference is a serious problem in switching power circuits. Here, the effect of frequency modulation on power supply EMI noise is investigated. Significant reduction of emission is possible with the proposed scheme. >

A procedure for designing EMI filters for AC line applications

A procedure for designing AC power line EMI filters is presented. This procedure is based on the analysis of conducted EMI problems and the use of a noise separator. Design examples are given, and results are experimentally verified.

Effects of parasitic parameters on EMI filter performance

Two filters with identical topologies and components can exhibit a significant difference in filter effectiveness when the layouts are different. The goal of this paper is to examine the effects of parasitic couplings among the filter components and the coupling between the filter components and the ground plane of printed circuit board (PCB). Specifically, six different coupling effects are investigated: the couplings between the inductor and capacitors, a filter inductor and trace loops, two filter inductors, two capacitor parasitic inductances, a filter inductor and ground plane, and two trace loops. Experiments were performed, theories were developed to investigate and characterize these parasitic couplings.

A MOSFET resonant synchronous rectifier for high-frequency DC/DC converters

A resonant synchronous rectifier which combines the fast switching of Schottky diodes with low conduction drop of MOSFET devices is discussed. The MOSFET devices are driven in a resonant fashion by the power circuit, resulting in partial recovery of the energy stored in the parasitic capacitances. Power loss in the resonant synchronous rectifier is determined as a function of various devices parameters and switching frequency. Contributions of conduction losses, gate-drive switching losses, and losses due to current circulating in the parasitic capacitances are discussed. The analysis indicates that, at megahertz range switching frequencies, a resonant synchronous rectifier has a significantly higher efficiency than either a PWM (pulse width modulation) synchronous rectifier or a Schottky diode rectifier.<<ETX>>

Separation of the common-mode- and differential-mode-conducted EMI noise

A device is developed to decipher common-mode and differential-mode noise from a conducted EMI noise measurement. This device is a useful tool for power supply circuit noise diagnosis and line filter design.

Passive cancellation of common-mode noise in power electronic circuits

It is well known that common-mode (CM) conducted electromagnetic interference (EMI) is caused by the common-mode current flowing through the parasitic capacitance of transistors, diodes, and transformers to ground in the power circuit. Because of the potential for interference with other systems it is necessary to attenuate this noise. Ordinarily this is accomplished by using a magnetic choke across the input power lines, resulting in penalties to the overall size and cost of the completed system. In order to lessen the requirement for this magnetic choke, there has been a desire to introduce noise cancellation techniques to the area of EMI. This text introduces a method of canceling the common-mode EMI by using a compensating transformer winding and a capacitor. Compared with other cancellation techniques, it is much simpler and requires no additional transistors and gate-drive circuitry since it merely adds a small copper winding and a small capacitor. By using this technique the size of the EMI filter can be reduced, especially for applications requiring high currents. In this paper, the new method for passive noise cancellation is applied to many popular converter and inverter topologies. The method, results, and ramifications of this technique are presented in order of appearance.

Inductor-less piezoelectric transformer electronic ballast for linear fluorescent lamp

This paper presents a cost-effective piezoelectric transformer based ballast circuit that is designed to drive a linear fluorescent lamp without dependence on any magnetic devices. This innovative circuit uses a radial vibration mode piezoelectric transformer or Transoner(R) to replace the inductor and the capacitors of the resonant tank portion in conventional electronic ballast circuits in order to effectively reduce the component number and cost. By fully utilizing the characteristics of the radial vibration mode piezoelectric transformer, the switches of the ballast circuit can work in a ZVS (zero-voltage switching) condition thus significantly reducing the turn-on switching losses when compared to a hard-switching topology. In addition, the inherent input capacitance of the radial vibration mode piezoelectric transformer enhances circuit operation by serving as a turn-off snubber for the half-bridge switches. This decreases turn-off voltage spiking thus reducing the turn-off losses for the half-bridge switches of the proposed circuit. Through these innovative circuit techniques, the proposed circuit provided 32-watts of power at commendable efficiency of around 90% when utilizing a standard 110-volt 60-Hz line as the power source and a 4-foot 40-watt linear fluorescent lamp as a load.

A Family of Zero-Voltage-Transition Bridgeless Power-Factor-Correction Circuits With a Zero-Current-Switching Auxiliary Switch

A novel zero-voltage-transition high-efficiency bridgeless power-factor-correction (PFC) circuit with a zero-current-switching auxiliary switch was proposed, analyzed, and experimentally verified. An assist circuit, consisting of a resonant inductor, two blocking diodes, a clamping circuit, an autotransformer, and an auxiliary MOSFET switch, was used to reduce the turn-on switching loss of the two main switches of the bridgeless PFC circuit and the turn-off switching loss of the auxiliary switch. The soft commutation of the main switches is achieved without imposing an additional voltage stress on the main switches. Feedback gate-drive signals can be obtained by using an existing converter IC controller modified to fit the purpose. In this paper, a detailed description of the circuit operation will be given. Based on the analysis, the guidelines for the component selection are presented. A prototype of 100-kHz 600-W universal-line PFC bridgeless circuit was built to verify the proposed scheme. In addition, based on the same concept, a family of bridgeless PFC configuration was proposed.

Mixed-mode EMI noise and its implications to filter design in offline switching power supplies

Analysis of the newly discovered mixed-mode EMI noises provides a better understanding of the filter attenuation mechanism. Many practical design issues are investigated from this point of view. Hopefully, the results given in the paper reduce the mystery and the cut-and-try process in filter design in offline power supplies.

A cold-cathode fluorescent lamp driver circuit with synchronous primary-side dimming control

A novel synchronous primary-side dimming control scheme is proposed and tested for a cold-cathode fluorescent lamp (CCFL) driver circuit for liquid crystal display (LCD) backlight illumination display applications. This new control scheme features high efficiency, even-dimming sensitive adjustment, even-brightness control for a two-lamp system, less lamp flickering problems, stable feedback control and simplicity. An analysis of the circuit is given, from which a design example is presented.