Input filter interaction with SMPS (11 of 13) |
Cascaded Converters and Multiple Converters on Common BusCascaded converters are used in distributed power systems where an ac-dc converter or a dc-dc source converter provides a regulated bus for several dc-dc load converters operating in parallel. Lewis et. al. showed that the negative input impedance of the load converters can introduce right-half-plane poles in the source converter and affect its performance. They develop a criteria for preventing this and for introducing a filter between the source and load converters. This is expanded into a simple design procedure by Choi and Cho in 1995. Martin Florez-Lizarraga and Arthur Witulski further develop these concepts in techniques in a 1993 paper and an updated 1996 paper. Do not use this information for design without independent verification of the information. Editor: Jerrold Foutz |
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Input filter interaction with SMPS (10 of 13) |
Current-Programmed CriteriaY-Parameters. Using y parameters, both the analytical and graphical criteria for determining stability and degradation with the addition of an input filter have been worked out by Erich-and-Polivka, and by Kohut. Erich-and-Polivka use impedance for their graphical criteria and Kohut uses admittance. |
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Input filter interaction with SMPS (9 of 13) |
Filter DampingInput Filter. Feedforward techniques have been proposed to prevent the peaking of the input filter from causing instability and performance degradation. See Kelkar and Lee for an example. This technique is controversial and not recommended by some investigators. However, the primary reason for damping the input filter is usually to control the amplification of input voltage modulation caused by the resonances of the input filter and feedforward should not be necessary. |
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Input filter interaction with SMPS (8 of 13) |
Practical Placement of Input FilterPlacement. P5 is the most practical placement of the input filter. Input L. In this location, added input inductance from a system EMI filter or long leads to the power source will not cause the power supply to go unstable since Ls will migrate to the left, which is safe, and will not increase the Q. |
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Read more... [Input filter interaction with SMPS (8 of 13)]
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Input filter interaction with SMPS (7 of 13) |
Placement of Input FilterNo Problem in the Old Days. When 20kHz switching-mode power supplies began to be used in the mid 1960's usually the only EMI specification invoked was for conducted emissions above 150kHz. This placed the input filter out to the right of location P1, beyond the negative input resistance frequency of the power supply, and adding a filter never caused instability. |
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Read more... [Input filter interaction with SMPS (7 of 13)]
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