Inrush current limit

Agree with Bengt Rehnström. ferrit bead can't help. you need some resistance, not inductance.

In the PC power supply, the bead core on the wire is for noise filter.

Some good reading:

http://www.eet-china.com/ARTICLES/2000DEC/2000DEC13_AMD_AN5.PDF?SOURCES=DOWNLOAD

Or just seash for "an1542" it is a more or less standard AN to read.

I have used inductiv, fixed value resistors, NTC and active MOSFET controll i designs in order to keep the inrush under controll - With EUP and for mbattery powered equipment it is not an option to use the NTC because it lowers the system over all effinency. One other option that is usefull in some situations is the PROFET from INFINEON - you have to check there datasheet - they have serveral different for different applications.

I have used some hot-swap control methods in my designs which does similiar functions like inrush/over current limiting....... which is same as mentioned in the article like soft turn on of a MOSFET.....

The inrush current is largely depends on the value of the bulk capacitor on the supply input(like dc-dc converter input cap) which are used as a temporary storage and it's value largely varies with the input voltage range.....

its always better to use the active control method such as turning on a MOSFET slowly initially to avoid the initial inrush.......but in this case, considering such solutions costly i would suggest to add an inductor in series with the input capacitor.......

NTC is also a good option since its available even in 20mohms at max current now but it can be a little bulky.......selection largely depends on what resistance value is required during the turn-on time(or what current to be limited).....

Hi, check out the FPF2123FPF2123 from Fairchild Semiconductor, its a load switch with programmable overcurrent limit, it will operate at constant current when the (programmable) limit is reached, otherwise it will just turn fully on. should solve your problem!

Let us know if that worked...

Hi, check out the FPF2123FPF2123 from Fairchild Semiconductor, its a load switch with programmable overcurrent limit, it will operate at constant current when the (programmable) limit is reached, otherwise it will just turn fully on. should solve your problem!

Let us know if that worked...

Hesener,

Thanks for the part #. I will investigate.

Zero

Hi, this is the circuit I use for limiting the inrush current on USB powered circuits on +5 V rail.

Changing the capacitor you can obtain a bigger delay.

Tommaso,

Thanks for the circuit drawing. I didn't think of USB's 5V system. That is very much like what I am designing. Thank you.

Zero