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Transient response of vicor module power supply with certain capacitance?

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Flyback

Well-Known Member
Hello,

We are doing a 1V5, 160A power supply as in the attached pdf.
We are using Vicor Power modules.

We must use the absolute minimum capacitance (the purple ringed capacitors) . How can we assess what is the minimum capacitance that we can use from a transient response viewpoint?…I believe the app notes don’t give enough data and we would actually need to build it and do transient response tests…do you agree?
After all, there is no data on the crossover frequency of the P024T048 module with “x” amount of output capacitance and therefore we must build and test.?

P024T048T12AL power module
http://www.vicorpower.com/products?productType=cfg&productKey=P024T048T12AL

VTM48ET020T080A00 …fixed ratio voltage converter
http://www.vicorpower.com/products?productType=cfg&productKey=VTM48ET020T080A00
 

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Flyback

Well-Known Member
And this is Related to the above.......Concerning Feedback loop bandwidth increase of cascaded SMPS converters?

Figure 1, Page 2 of the P024T048T12L power module datasheet (below) shows a setup involving a SMPS which comprises a regulation stage followed by an “electronic transformer” voltage down converter stage. Page 2 of this datasheet states that this setup gives “bandwidth and speed advantage“
Why is this?
Since when did cascading a regulated SMPS with a fixed conversion ratio voltage converter mean you can get faster feedback loop bandwidth?

P024T048T12AL power module datasheet
http://cdn.vicorpower.com/documents/datasheets/24V_48V_120W_PRM.pdf

VTM48ET020T080A00 …fixed ratio voltage converter datasheet
http://cdn.vicorpower.com/documents/datasheets/VTM48E_020_080A00.pdf
 

ccurtis

Well-Known Member
My quick perusal through the vicor docs does not indicate a need for any capacitance where you have placed circled capacitors. Although I see caps located in those areas in one application note, there is no mention of them in the note. The internal input and output capacitance of the modules is already quite large (5uF), so that is the minimum capacitance achievable.

Vicor has an applications assistance contact number that is a good place to ask, since this is a issue specific to a complex vendor-made module.
 
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Tony Stewart

Well-Known Member
Most Helpful Member
The fixed ratio regulator takes advantage of transformer turns ratio to boost current, lower output impedance and thus does not need to be concerned with load regulation as Zout is <~ 1mΩ. Thus ratio control based on input voltage can be done with a much faster regulation as the expected ratio input range is small.

Load regulation errors can be closed loop or feed forward corrected in the pre-regulator.

adding large caps is not necessary where you have shown except primary input {1000uF}
Victor will have an app. guide to indicate min, max C range for output caps.
Find it.

app note. http://cdn.vicorpower.com/documents/application_notes/vichip_appnote24.pdf
calculator http://spicewebprd.vicorpower.com/apps/PRM_VTM_Calculator/Calculator.php

Don't underestimate Vicor's documentation. It is very thorough, but you should test and verify with Bode Plots with load and thermal regulation.

Their efficiency is outstanding using GaN switches for ratio converter with ZVS & ZCS.
 
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