Grass Valley SMS-6000 Series - Manual (Page 32)

1-15
Power System
Power System
1RU frame, can have only a single power supply, whereas 2 or 3RU frames
have the option of dual supplies to protect against the failure of one of the
supplies or, the loss of incoming AC power on one power bus. There are
two AC power connectors so that a backup supply can be fed from a
completely separate power lead, thereby offering maximum protection
against loss of power. The AC connectors are located on the rear panel and
incorporate a fuse and adjacent voltage selector for convenience during
installation.
A traditional transformer system in the rear of the matrix frame is used to
step down the mains voltage to around 20 volts AC. On the plug-in power
module the AC voltages are rectified and smoothed to produce raw DC
rails of 20–30 volts. Low voltage switching techniques are then used to
convert the raw DC into the smooth DC voltages used on the router
modules. This method has the benefit of low heat generation without the
high stress of mains voltages on the components found in traditional
switch-mode designs. These features both contribute to high reliability.
CAUTION
Different modules need different power rails and these rails are selected by jumper
links on the power module. If the incorrect module is plugged into a frame, then
permanent damage may be caused to the main module. Some modules are
installed with a linearly regulated third (+12V) rail to drive a cooling fan.
A standby switch at the front of each Power Supply (PS) module enables
the DC power to be switched off but does not disconnect the mains power.
Cooling Fan - 1RU frame
On some frames a cooling fan installed on the right-hand side of the frame
draws cool air from the side and expels it through the vents along the left-
hand side of the frame. The Power Supply module provides the 12V DC
supply for this purpose, which is not switched by the standby switch on the
PS module so the fan will always run when the power cord is plugged in.
Cooling Fan - 3RU frame
The cooling fan installed in the rear of the frame draws cool air from the
rear and expels it through the vents along the left-hand side of the frame.
It is powered from both power modules, so that if either fails then it
continues to run. The Power module provides the 12V DC supply for this
purpose, which is not switched by the standby switch on the PS module so
the fan will always run when the power cord is plugged in.