Theory of operation
Combiner boar
d
The Combiner board routes the 100-240 VAC input from the rear-panel line filters
to the Power Supply modules. The AC level detectors on the Combiner board
indicate if t
he AC level is less than about 75 V. These AC-low lines drive the
front-panel AC LEDs and the logic in the Combiner board and Main board PLD
to prevent switching if the AC inputs are low.
The Combiner takes in the 12 V from the one or two supplies, and converts
it to 5.2 V for the rest of the instrument. If there are two good supplies, the
microcontroller in the Combiner chooses the preferred one. If either supply or AC
input has an issue, the microcontroller chooses the best one.
There are two sets of 12 V storage capacitors. One set of capacitors allows time
for the system to switch supplies without any disruption of the 5.2 V output. The
second set of capacitors is used to flash the power-status LEDs for approximately
10 minut
es after loss of power. During the boot up of the Combiner board
microcontroller, the Combiner functions in diode mode and uses whichever
supply has the higher voltage, or a mix of the two.
During operation, the Combiner board has a load that can be used to test the
inactive supply. This happens when a new supply is plugged in and once a day to
ensure that the backup supply can support the instrument if the primary supply
fails.
The Combiner board also drives the fans and senses if they are not spinning. The
fans are located in each Powe r Supply module.
ECO8000 Series Service Manual 2–9
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