Ripple current cancellation circuit
ABSTRACT A ripple current cancellation technique injects AC current into the output voltage bus of a converter that is equal and opposite to the normal converter ripple current. The output current ripple is ideally zero, leading to ultra-low noise converter output voltages. The circuit requires few additional components, no active circuits are required. Only an additional filter inductor winding, an auxiliary inductor, and small capacitor are required. The circuit utilizes leakage inductance of the modified filter inductor as all or part of the required auxiliary inductance. Ripple cancellation is independent of switching frequency, duty cycle, and other converter parameters. The circuit eliminates ripple current in both continuous conduction mode and discontinuous conduction mode. Experimental results provide better than an 80× ripple current reduction.
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ABSTRACT: This paper describes a patent-pending passive offline light-emitting diode (LED) driver that has no controlled semiconductor switches, electrolytic capacitors, auxiliary power supply, and control board. It can provide a fairly smooth current from the ac mains to drive LED strings. The new circuit has the advantages of high input power factor, high energy efficiency and luminous efficacy, long lifetime, stable luminous output, and high robustness against extreme weather conditions. In addition, over 90% of the driver material is recyclable, leading to reduction of electronic waste. It is particularly suitable public LED lighting systems, such as road lighting systems. Experimental results based on a 50-W system are included in the paper to confirm the validity of the proposal. Due to the circuit simplicity, an energy efficiency exceeding 93.6% has been achieved.IEEE Transactions on Power Electronics 11/2010; · 4.08 Impact Factor
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ABSTRACT: Design of electrical EMI filters requires an in-depth understanding of the desired frequency response. While low frequency filter performance (below 2-5 MHz) often matches the expected response, at higher frequencies the actual filter attenuation is generally much worse than expected. Traditional explanations involve the self parasitics of the reactive devices, equivalent series inductance (ESL) of capacitors, and equivalent parallel capacitance (EPC) of inductors. This paper demonstrates that the parasitic mutual coupling across successive filter stages plays an important role in degrading filter attenuation performance at high frequencies. An example filter is constructed, and it is shown that the performance is heavily influenced by the mutual inductance and mutual capacitance between the components. Techniques to measure these parasitic parameters are provided, as well as methods to reduce these parasitics and improve the filter attenuation. Circuit simulation results show excellent agreement with the measured filter performance, and demonstrate the filter degradation due to the self and mutual parasitics. Electromagnetic interference (EMI) filters are used in power electronic systems to mitigate high frequency noise problems. Measured filter performance is often much worse than the expected behavior due to electrical parasitics. Improved electrical filter attenuation can be obtained by understanding and minimizing the important filter component parasitics. Electrical filter performance is heavily dependent upon construction methods and layout. The characteristics rely upon the nominal device parameters, self parasitics such as equivalent series inductance (ESL) and equivalent parallel capacitance (EPC), and also upon mutual parasitics. The dominant mutual parasitics are mutual inductance and mutual capacitance. This paper presents a third order electrical filter, and demonstrates the importance of the parasitic components on the filter attenuation. Experimental results validate the filter performance degradation over a wide frequency range due to the parasitic components. Electrical simulation results provide excellent agreement with the measured performance. Previous papers have demonstrated how to cancel or minimize filter parasitic coupling (1-3). These methods increase the desired attenuation of the filters, but often require novel construction methods, added electrical components, or other electrical modifications to obtain the desired results. In this paper the effect of relatively minor layout construction differences are shown to have a strong impact upon the filter attenuation characteristic. A simple pi-filter circuit is used to demonstrate the effects of how construction and layout differences affect the filter attenuation. Measurements performed over a large frequency range demonstrate the wide bandwidth applicability of these techniques. The paper demonstrates how the filter parasitics affect the overall filter attenuation performance. Electrical measurements are performed using a spectrum analyzer and tracking generator. These results experimentally confirm that simple modifications to a filter layout can strongly affect the attenuation characteristic. A simple SPICE model demonstrates excellent agreement with the experimental results, and illustrates the filter degradation due to self and mutual parasitics. Mutual inductance is one of the dominant characteristics that affect filter attenuation. A discussion of mutual inductance and its interaction upon electrical components is discussed in detail. A simplified example of two circular, filamental loops is used to demonstrate how mutual inductance varies as the loops are placed in different positions relative to each other. Mutual inductance can be made to go to (nearly) zero using a simple geometrical offset of the loops. This method of reducing mutual inductance between two loops is used to improve the filter attenuation performance over a wide frequency range.01/2011;
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ABSTRACT: This paper presents a novel isolated buck converter with output voltage ripple reduction by a complementary square-wave scheme. The converter is composed of a forward DC-DC converter, a half-bridge inverter, and a common LC filter. The outputs of forward converter and halfbridge inverter are connected in series, so that their square-wave outputs are added to form one constant DC voltage. The LC filter is used to remove the output ripples, which are induced by light loading, and noise of the DC voltage so as to obtain a steady output voltage. The circuit can also lower the switching frequency, and decrease the circuit transient response effect of one LC filter. So it is one easily controllable isolated DC-DC buck converter with high stability and low cost. Simulation results have been provided confirm the proposed method. Experiment will also be done soon to verify the performance.01/2011;