Platinum Z5 CD - Single Phase PA Power Supply; Rectifier Board

888-2408-002 4-25
WARNING: Disconnect primary power prior to servicing.
Overall System Theory
4.5.2 Single Phase PA Power Supply
Refer to the Overall System Block Diagram in the schematic package for the
following discussion. The transmitter single phase AC inputs connect directly to
K1, the AC mains contactor. The transformer side of the contactor is wired in
parallel to power transformers T1 and T2 primaries in the bottom of the transmitter.
T1 and T2 primaries must be tapped for the proper AC input voltage. The tapping
chart can be found on the Overall System Block Diagram. T1 and T2 can
accommodate input voltages in the range of 198 to 250 Vac.
Each transformer one center tapped secondary with the center connection being the
rectified DC output of 52Vdc. The DC output are filtered by L1, C1, C15 and C16
for T1, and L3, C2, C25 and C26 for T2. Each of the transformer secondary taps is
connected to an SCR which is controlled by ON/OFF signals from the PS Controller
board via the Rectifier Board.
The secondaries of T1 and T2 use the unique tap switching design to give a small
window of coarse regulation (approximately 2Vdc change per tap) to compensate
for AC line variations.
4.5.2.1 Rectifier Board
The SCRs for the single phase are required to carry a much larger amount of current
than the 3-Phase counterparts and are therefore much larger. They are mounted on
large heatsinks on top of the transformers. The SCRs are used for the tap switching
as well as rectification of the AC voltage. Each transformer secondary winding has
8 taps. Each of these taps have one SCR to ground. The secondary is full wave
rectified, which means that one SCR on each side of the center tap is used for each
voltage level. For example CR1 and CR5 on either transformer will be active at the
same time. The other pairs are CR2 and CR6, CR3 and CR7 and CR4 and CR8. The
Power Supply Controller can turn on any pair of the SCRs at a given time. If the
voltage is not high enough at the DC output, the PS Controller can change the
transformer turns ratio by turning on a different SCR pair and therefore utilizing a
different secondary tap. The taps closest to the center will provide the least amount
of secondary turns in circuit and will therefore give the lowest DC output voltage.
This means that the taps which are furthest from the center will give the highest DC
output voltage due to more active turns in the secondary.