SA7x Technical Description
2.5 SA7x Power Supply
The individual regulators are enabled or disabled by the control lines A through
D. These lines are connected to the dc drive power switches on the front panel.
Setting a switch controls both the +5.1 Vdc and +12.1 Vdc outputs for each drive.
The overcurrent protection circuit allows a short circuit to be present at any
one, or all, of the outputs for an unlimited time without permanent damage to
the supply. A hiccup timer on the output of the overcurrent protection circuit
continually attempts to reset the outputs during the overcurrent condition.
When the overload is removed, the power supply outputs automatically return to
normal.
The overvoltage protection circuit shuts down the power supply in the event
of an overvoltage condition at any one of the outputs. Because the overvoltage
protection circuit output is a latched shutdown signal, the supply must be turned
off, then on again, to reset this circuit.
In addition to monitoring at the pulse width regulator level, the individual
regulators for each disk drive are also monitored by sense circuits A through D.
These circuits sample the voltages out of the individual regulators and produce
both a latched shutdown signal and an indicator drive signal. The indicator drive
signal is displayed at the associated drive power switch to indicate that normal
power is being supplied to the drive.
The thermal shutdown signals come from the TB2 fan OK signal and from an
on-board temperature sensor. The overtemperature controller monitors both these
inputs and produces a thermal signal for a shutdown driver. Thermal shutdown
indicated by a red Fault indicator visible through the upper-rear panel of the
power supply. There are two temperature monitor circuits in the enclosure. TB1
contains a temperature sensor to monitor the incoming ambient air temperature
and regulate fan speed. The temperature monitor in the power supply monitors
the air temperature in the vicinity of the power supply, including enclosure
exhaust air, and produces the actual shutdown signal.
The THERMAL signal is also monitored by a power OK circuit which produces
an ACOK signal if the +300 Vdc regulator outputs are valid or if the temperature
in the enclosure is within operating limits. The ACOK signal is passed to TB2
and then to the disk drives. This signal warns the drives to complete operations
in the event of an enclosure shutdown.
2–12 SA7x Technical Description
