Inrush module for input filter

[cupoftea]

Hi,
Do you know of any nice cheap offtheshelf
inrush modules (smd) for the attached input filter.?
We think surely there must be, its a general ubiquitous situation.
Otherwise we will have to do discrete.

As is known, The three 0.33Rs are MMB0207...they will not survive the inrush transient. Hence we need the inrush limiting.
The three MMB0207s are needed because the electro caps are not rated for the ripple current, which is 7A ACrms, into the Buck converter.

 

[KlausST]

Hi,

filter or inrush_current_limiter?

For DC inrush current limiter there are so called "hot swap controllers".

Klaus

 

[scopeprobe]

Hi,
Do you know of any nice cheap offtheshelf
inrush modules (smd) for the attached input filter.?
We think surely there must be, its a general ubiquitous situation.
Otherwise we will have to do discrete.

As is known, The three 0.33Rs are MMB0207...they will not survive the inrush transient. Hence we need the inrush limiting.
The three MMB0207s are needed because the electro caps are not rated for the ripple current, which is 7A ACrms, into the Buck converter.

Can you use more inductance and less capacitance in the filter? You'd get the additional reistance of the higher inductance, more impedance and also less capacitance.

 

[cupoftea]

Thanks, but no we cant use higher L...we need the cheapest and smallest.

Am actually wondering whether the attached inrush pulse will be dangerous, after several years of this once per day.
Ie, this inrush pulse into the 470uF, 50V capacitor EDH447M050A9SAA.
(LTspice also attached)

Its actually impossible to know what the ESR is thats relevant to this....i mean, what "frequency" would you say would the ESR be correspondent to?
We can get a frequency sweep of Z vs Freq....but then there's the internal Ce across the ESR...and that deffo isnt stated in the datasheet.

EDH447M050A9SAA 470uF, 50V El cap

https://www.mouser.co.uk/datasheet/2/447/KEM_A4049_EDH-3316662.pdf

 

[FvM]

I wonder if it's a realistic inrush current waveform? How is the voltage switched?

 

[cupoftea]

Its as though its been hot plugged.....ie, a sudden voltage step.
(BTW, budget wont stretch to a hot swap control chip......maybe a cheap FET switched inrush resistor...but is that needed?, or do we rely on the
legendary pulse withstanding capabilites of wet electrolytic dielectric?)