Users Manual & Installation Guide
PV- 5127:
Power supply module with UPS
Page 22 of 31
ATX and Softoff state machines
The PV-5127 provides several ways to turn on/off power. ATX compatible CPUs can turn
themselves on and off using PS_ON, and UPS monitoring software on CPUs without PS_ON can
turn off using either a RS232 handshake signal or a software command through the PC/104 bus.
Regardless of the method, the system temperature ensures that the CPU can only be turned on when
the system temperature is OK, but it is allowed to stay on if the temperature later becomes too cold
or too hot. The system temperature circuit can be bypassed using a jumper that effectively tells the
PV-5127 that the temperature is always OK.
The main DC/DC converter and 5V STB
The main DC/DC converter converts the input voltage (from mains or the backup battery) to 5V.
The output of the converter is directly connected to the 5V STB output, so whenever the converter
is on, the 5V STB is present. It also powers the internal control logic. When off, the power
consumption is minimal.
The output of the converter is also connected, through a power switch, to the main 5V output and
(through a step-up DC/DC converter) to the 12V output. The power switch controls when to turn
on the 5V+12V outputs.
The main DC/DC converter turns on when mains appears, and stays on as long as mains is present.
When the converter is on, the CPU can turn on and off the 5V+12V output using PS_ON,
depending on temperatures etc.
When mains disappears, the converter stays on as long as the 5V+12V output is on, and the battery
is OK (>9.5V). That is, when running on battery, the converter is turned off when the CPU turns
itself off (to conserve battery capacity until mains comes back), or when the battery is empty (to
protect the battery against deep discharging).
The 5V+12V outputs
The power switch, which turns on and off the 5V+12V outputs, is controlled by two state machines
implemented in the control logic – the ATX on/off state machine, and the Softoff state machine.
Both state machines must be in their “on” state for the power switch to turn on. When either state
machine goes to an “off” state, the 5V+12V outputs turn off, and if mains is not present, the main
DC/DC converter also turns off.
