Hardware reference guide

Pwr. & Grnding. Guide
786
35013379 02 October 2007
System Design Considerations for Quantum Power Supplies
Overview There exist some important design differences between various models of Quantum
power supplies that require careful consideration by the system designer in order to
achieve maximum system performance. The principal difference lies in the
generation within the power supply of important backplane signals related to the
health of the power supply and the status of the input power.
All Quantum power supplies include on-board early power fail detection logic which
is used to signal all other modules on the backplane that input power has failed. This
signal is called POK (power OK) and is active high (i.e., when the signal is high,
power is OK).
There is both an internal (to the power supply) and an external (as seen by the
backplane and all other modules) version of the POK signal. The internal POK signal
is represented by the Pwr ok LED (light emitting diode) on the front panel of all power
supplies.
The system POK signal is generated so that there is sufficient time between the
negative going edge of system POK (power has failed) and the actual interruption of
power to the backplane. This early warning of power failure is necessary for the
Quantum executive to perform an orderly system shutdown.
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com