Specifications

Chapter 7: Theory of Operation
Power Supply
133
Power Supply
The power supply is a +12 V bulk supply that is removable, exchangeable, and safety-
approved. It transforms AC power to the main +12 V 100A supply and a small +5 V
supply. The +5 V supply is standby power and is always on whenever AC power is
applied. The +5 V supply is used only by supervisory circuits that monitor and control
all other supplies. In the event of a safety shutdown from the supervisory circuits, LEDs
turn on to indicate the cause of the shutdown. They remain lit until AC power is
removed from the bulk supply.
The +12 V bulk supply is used to create all other supplies in the instrument. +12 V is
turned on by the power switch on the front panel. It is turned off under software
control when a shutdown is requested, or by the supervisory circuits when a fault occurs.
The +12 V bulk supply performs some internal fault sensing and drives LEDs on the
backplane board to indicate its status. It also provides an I
2
C bus, which is connected
to the main FPGA.