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Why use diff mode inductors rated for 6A(rms) when Input current is only 833mA(rms)

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treez

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Hello,
At one company where I worked, they had done a 100W Offline flyback SMPS (120VAC input), and had used four large diff mode inductors in the AC input filter that were rated for 6Arms of current.
(it was actually a Dual isolated PFC'd flybacks for 100W total)
Their is a total of 236nF of ceramic capacitance downstream of the rectifier bridge on the HVDC bus.

Their input filter schem is as attached.

Why had they used such high current inductors? There was a suggestion that it was because they would not saturate under transients. This was an aerospace application. The power supply would be used on civil passenger aircraft to provide a voltage bus for led lighting.

Why use such overly high current rated inductors?

This is the inductor datasheet…..
74437429203151 inductor
https://katalog.we-online.de/pbs/datasheet/74437429203151.pdf

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By the way, the SMA TVS that you see on the schem is the only transient protection component on the entire schematic.
 

Attachments

  • Input filter.jpg
    Input filter.jpg
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Same reason... need to not saturate in transient regim.
If that would happen may lead to destructive demage (present as a shot-circuit for upstream eq.) or at least blown of fuse... if is too fast.
 

Thanks, but as you know, there are other ways to fight surge damage, that dont involve needing to use input filter diff mode inductors rated at nearly eight times the nominal input current to the product.
 

low heat dissipation, high transient capability, - they were in stock ...
 
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Thanks, thats very true, but the size of these four inductors on the PCB......do you know if this use of massively over-rated inductors is common tro fight transients?
 

depends on the size of transient you are required to resist - in avionics it could be quite important ...!
 

Thanks, but this was just a power supply for the led lighting in the aircraft....though maybe that could be important i admit.

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I must admit i read DO140, the avionics standard, and it was difficult to see from there what the transient withstand was required to be.
 

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