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One of the major problems with Panel Testing is the multiplexing of power supplies. If there are more panels than power supplies
available, the panels must share supplies. If any panel attached to a particular power supply has a short condition on the
power node, all panels attached to that supply are rendered untestable. This document demonstrates a method of isolating one
power supply on 1 of 16 panels using eight General Purpose Relays.
In the figure below the panels are arranged as four rows by four colums. The ground node on each of the four boards in
a row are chained together to a GP Relay, whose other contact is tied to Power Supply Minus. The power node on each of the
four boards in a column are chained together to a GP Relay, whose other contact is tied to Power Supply Plus.
By closing one of the four power node relays (GP#1-GP#4 in the figure below) and one of the ground node relays (GP#5-GP#8
in the figure below) a single panel is isolated to the power supply.
This method could be expanded to handle a very large number of panels, limited only by the GP Relays available.
Some things must be considered when using GP Relays to apply power to a board. I personally recommend closing the relay
before applying power, and disconnecting power before opening the relay. Also observe the current limitations of the GP Relays.
The power supply current limit should be set to a value that will protect the relay should an assembly have a direct power
to ground short.
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