From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-03-13 10:28:21
Hi,
----- Original Message -----
From: Sar Saloth <sarsaloth_at_yahoo.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Tuesday, March 12, 2002 11:40 PM
Subject: [buildcheapeeg] patient over current protection
> Hi Joerg, more question.....
>
> >Jeorg wrote....<snip> * ESD and patient overcurrent protection <snip>
> >
>
> Is the over-current protection your input stage with the bipolar
> transistors?
Yes.
> Do you know what emails describe the operation?
Some descriptions and simulation results can be found in:
From: Joerg Hansmann <info_at_jhansmann.de>
Sent: Monday, January 07, 2002 7:51 PM
Subject: Re: [buildcheapeeg] Re: Input protection
From: Joerg Hansmann <info_at_jhansmann.de>
Sent: Sunday, January 06, 2002 5:40 PM
Subject: Re: [buildcheapeeg] Re: Input protection
> What sorts of events are you protecting for that would cause a dangerous
> over-current but would not have a voltage so great as to be greater than
> the transistors can block? (Did I understand that correctly?)
Shortcuts on the pcb or failures of the 1st input stage that
connect +5V and AGND to the EEG electrodes and thereby exceed
the IEC601-1 maximum 10uA DC through the patient.
The problem was how to protect the patient and simultaneously
not to put too much additional resistance in series with the inputs
(what would result in increased noise due to the noise current from the
INA114 inputs) or add more risk by an active circuit that could fail
itself.
I am not too happy with this input protection because some failure
conditions can occurr (see I/U diagramm in the above mentioned posting)
that it will not resolve.
What do you think ?
Regards,
Joerg
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