ICD2's go bang when you get this wrong.

Using an isolated 130v dc with a pair of class y caps (4n7) to earth the
stored energy in these burst the icd when it was plugged in the wrong order
the power supply was fully floating. 

The 0v (-ve supply) or the shell of the comms port is connected to earth. In
my apps it's the battery -ve and is now a copper link around the icd... the
usb is not isolated from the application.....

Rgds steve 



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Alan B. Pearce
Sent: 08 June 2007 08:47
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] ICD 2 Advisory (Grounding Question)

>I don't understand the need to have the system interface
>floating when programming a non-isolated AC-powered target
>device. I assume by "non-isolated," they mean the target
>device's ground is an earth ground

By 'non-isolated' I think they mean there is no transformer in the mains 
supply to the target device, when running off mains power. Personally I 
would be very worried about doing this as it means all the test equipment is

connected to mains potential, and hence potentially (no pun intended) 
lethal.

On the other hand they may be talking about the earth, as it could be 
possible to have an earth loop through the ICD and test equipment back to 
the mains earth, as well as the earth direct from the target to mains earth.

This could induce significant fault currents around the loop, and may be the

cause of ICD buffers being destroyed (as has been reported here at various 
times). 

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