- #1

Ntip

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- TL;DR Summary
- How do I go about selecting a reasonable frequency response and cutoff frequency?

I am starting the input filter design for a converter and only have the voltage and power specs. It will be the input filter to other converters on a parallel bus, so I could look at the datasheets for those and get some specs there. I do not have any information from the input converter to this bus, I just know the voltage is regulated and the power it will be supplying. I'm not sure what specs to look at to determine what I should set as my cutoff frequency or how to determine an appropriate target frequency response. Does having parallel converters on the output complicate things, or do I just look at the worst case converter (I'm not really sure what to look at either way)?

I was going to start off with a DM and CM filter design but I'm not sure how to determine if I need both DM and CM since the input and output will be regulated. Also, the the output and assuming the input both have DC/DC converters, they likely already have their own capacitance. How is this factored in?

I was going to start using Heavyside's criterion for stability so require Zo << Zin or Zo=1/10*Zin where Zo is the output impedance of the filter and Zin is the input impedance to the bus. Zo can be calculated using Zo=sqrt(L/C) and Zin=(Vin^2*efficiency)/Pout. Pout would be the output power from all converters on the bus added together. I guess I should use a lowest power output to increase Zin and further reduce the Zo requirement?

I have questions about setting Zo=1/10*Zin because does this still hold when the input filter is between two regulated DC/DC converters?

I have a lot of questions and not many unknowns. I'm sure I'll create more questions for myself once I really start digging into this design. Any help is much appreciated.

Nick

I was going to start off with a DM and CM filter design but I'm not sure how to determine if I need both DM and CM since the input and output will be regulated. Also, the the output and assuming the input both have DC/DC converters, they likely already have their own capacitance. How is this factored in?

I was going to start using Heavyside's criterion for stability so require Zo << Zin or Zo=1/10*Zin where Zo is the output impedance of the filter and Zin is the input impedance to the bus. Zo can be calculated using Zo=sqrt(L/C) and Zin=(Vin^2*efficiency)/Pout. Pout would be the output power from all converters on the bus added together. I guess I should use a lowest power output to increase Zin and further reduce the Zo requirement?

I have questions about setting Zo=1/10*Zin because does this still hold when the input filter is between two regulated DC/DC converters?

I have a lot of questions and not many unknowns. I'm sure I'll create more questions for myself once I really start digging into this design. Any help is much appreciated.

Nick