Ok, I have 0 EE background, so this may be a very simple question.

As I understand it (from various info gleaned from googlling), Inrush current is a surge in current that occurs upon power-on of an electronic device. From what I've read about inrush limiting, this is always done at the power supply level.

Does this mean that in a modular device such as a bladeserver chassis or switch/router that the modules themselves are not subject to inrush current, as this is only an issue at the power supply level?

Also, any good references that you may have would be appreciated. I found several docs via google, but most of the results focus on specific types of components for sale rather than the theory.

[Edited on July 27, 2006 at 11:25 AM. Reason : aasg]

7/27/2006 11:23:02 AM

Now I really wish I didn't stick with CSC... CPE/EE would have been far more relevant.

7/28/2006 9:22:32 AM

The basic theory is that when you apply power to any circuitry, the instantaneous step response will not be the same as the steady state response. For example, there will be capacitance throughout the circuit that will, instantaneously, act as short circuits as they being to charge. As another example, some parts have electrical characteristics that change as they heat up.

In the case of several modules connected to a power supply, the maximum inrush current to each module will depend on the power supply. A quality power supply will have some current limiting capabilities, so you'll get some protection there. In addition, the individual modules should limit the current on the inputs from the power supply, so in a sense, you are doubly covered.

In a system like the one you're talking about, you can use a scope with a current probe and measure the current as you power on by attaching it around the power wires to get an idea of how the inrush current compares to the steady state current.

7/28/2006 10:14:06 AM

sonofabitch, ^ beat me by 1 minute




[Edited on July 28, 2006 at 10:15 AM. Reason : .]

7/28/2006 10:15:26 AM

^^ awesome, thanks!

7/28/2006 10:20:58 AM

Just like on motherboards, the PSU powering things most likely has a power good feature anyway where it isn't going to actually power the outputs until the voltage is stable.

7/28/2006 10:21:25 AM