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WARNING: Disconnect primary power prior to servicing.
Overall System Theory
4.7.5.1 Power Supply Turn On
The primary function of the PS Controller is to turn the power supplies on and off.
The on/off signal is called PS_DISABLE and comes in on J3-13. The signal
originates on the Master Controller but passes through a logic gate on the Life
Support Board before reaching the PS Controller. PS_DISABLE is an active high
signal which means that if the signal is high the power supplies will be shut off.(the
secondaries will be deactivated by shutting of the SCRs but primary voltage could
still be present). If it is low, the power supplies will be activated, unless there is a
critical fault on the PS Controller board, in which case the supplies will be shut off
regardless of the PS_DISABLE signal. The power supplies are turned on via one of
the four outputs:
• DRIVER 1 (TAP 1 - 48V)
• DRIVER 2 (TAP 2 - 50V)
• DRIVER 3 (TAP 3 - 52V)
• DRIVER 4 (TAP 4 - 54V)
These outputs are duplicated, one set for PS1 and the other for PS2. When the
transmitter is turned on the Master Controller brings the PS_DISABLE signal low
(provided the contactor has been activated and the Master Controller is operating
normally). This will first activate the SOFT_START outputs at J1-8 and J2-8. This
allows the supplies to charge slowly, limiting the in-rush current via the soft-start
resistor and SCRs on the rectifier boards. The supply voltage must reach at least
40Vdc within 3 seconds (6 seconds for a Single Phase supply), otherwise the turn on
sequence will be aborted. After 3 (or 6) seconds, if the voltage is within tolerance,
the PS Controller will activate the lowest available voltage tap by activating one of
the four DRIVER signals. Since DRIVER_1 is connected to the 48V tap, it will be
activated first (if available) and the power supplies will come up to full charge.
The PS Controller will now check the power supply voltages via the DC Voltage
Samples from each power supply. These come into the board at J1 and J2, pins 13
and 14 from the rectifier boards. These signals pass through U7 which acts as a
linear amplifier and buffer to prevent the analog samples from overloading the front
end of the A/D converter in the micro controller IC, U6. Using these samples the PS
Controller will determine when and if it is necessary to change taps to increase or
decrease the DC PA voltage. It will try to maintain the voltage as close as possible
to 52Vdc.
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