Input Over-voltage protection during Power Off

[Mnuet]

Hi,

  I am using NI-PCI-4474 & NI-PCI-4472B for my data acquisition application. The normal input voltage range is +/-10V while input over-voltage protection range is +/-42V. Now if the PC in which these devices are installed is powered off, will the input over-voltage range will remain same? Actually in our application, there may be a chance that input signal is coming while these devices are powered off. Do I need to use some extra protection mechanism in this case?

[aNIta B]

Hi Mnuet,

        Because the over-voltage protection is so high, our specifications don't specifically list an over-voltage protection for when the power is off (it is typically less, but shouldn't matter much in this case).  I will double check on this to be sure.  I'm very curious though, what kinds of voltages are you going to be putting on your device? Please let me know, and I will continue to look into this as well.  Thanks!

[Mnuet]

Hi aNIta B,

  Thanks for your support.  

Basically input voltage signal will remain in the range of +/-10V (and worst case +/-25V) when device is powered off. I am just concerned since usually for an operational amplifier present at input stage, if there is no input current limiting mechanism, the input voltage can damage operational amplifier if its supply voltage is cut-off (which will obviously be the case when device is powered off). This is what typically mentioned in operational amplifier datasheets. Also if over-voltage protection (+/-42V) is based upon active components then it should also be dependent on supply voltage condition.

I hope you understand my point now. I shall be waiting for your expert advice since you may be much more aware about the input circuitry and protection mechanism used.

[aNIta B]

HI Mnuet,

           You make a very valid argument, and unfortunately I haven't been able to find a better spec than what is listed in the detailed specifications of that device.  The R&D engineer who works closely with this product has been out of the office, but I'm hoping to find out a little more information from him when he gets back.  Thanks for your patience!

[aNIta B]

Hi Mnuet,

            I talked to the PSE for this product today, and he is going to double check on it.  However, he said that because the specification isn't listed as specifically the powered-on over-voltage protection that spec should apply to both the on and off states of the card.  He also agreed that you made a valid point, but thinks that is accounted for in that specification. He's going to double check, so I'll let you know if he tells me otherwise.  Take care!

[Mnuet]

Hi aNIta B,

   Thanks for your support in this regard. I also hope that the specifications should be same in both cases. However I shall appreciate if u can confirm this.

Thanks & Regards

Mnuet

[aNIta B · Accepted solution]

It's confirmed!  It's been verified by a few of our R&D engineers that indeed, that is the over-voltage protection for when the card is both on and off.  Take care!