# How to find Power-on Surge Current

P

#### Pon

Jan 1, 1970
0
Hi,

How to calculate the Power-ON surge current of a IC. . Shall i take
the maximum current as Power-ON surge ? But normally this Inrush
Current will be higher than the Maximum current of the operating
current IC

M

#### Mac

Jan 1, 1970
0
Hi,

How to calculate the Power-ON surge current of a IC. . Shall i take
the maximum current as Power-ON surge ? But normally this Inrush
Current will be higher than the Maximum current of the operating
current IC

Why do you need to know this?

Normally, the power-on surge current of the capacitors on the board is
much larger than power-on surge current of the IC's.

If you really do need to know, call the vendor's applications engineers or
buy some chips and measure the inrush current.

--Mac

D

#### Dan Fraser

Jan 1, 1970
0
ICs generally do not have a turn on current surge.

When a turn on surge occurs, it is caused by the charging of the capacitors
in a circuit.

To measure it, I put a 0.02 ohm resistor in series with the circuit and
watch the surge with an oscilloscope. Then I calculate the surge current
(Peak voltage / .02)

It is tricky when doing AC operated equipmnent. For them I have a 50A
isolation transformer. A smaller one will work but this reduces te size of
the surge because of the transformer's source impedance.

Dan

P

#### Pon

Jan 1, 1970
0
My board consists of various power supplies. +5V is the only input for
my board. I am generating all the other supplies such as
+3.3v,+1.8v,+1.5v and +1v by buck convertor circuits in the board. I
only designed the buck convertor ckt also.

My board contains four processors each will consume max of 4A while
operating condn, So there may be a chance of inrush current to the
processor IC's.In that case i need to design the buck convertor ckt in
such a way that it withstand the surge. That's why i am asking this.

P

#### Phil Allison

Jan 1, 1970
0
"Dan Fraser"
It is tricky when doing AC operated equipment. For them I have a 50A
isolation transformer. A smaller one will work but this reduces the size
of
the surge because of the transformer's source impedance.

You only need to isolate the voltage across a current sense resistor in the
AC supply with a small transformer.

Or, better still, use a Hall Effect transducer if response to DC is wanted.

http://www.farnell.com/datasheets/37259.pdf

......... Phil

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