4.3 FPS Theory of Operation
Section 4: Theory of Operation
CV-12SLX User Manual
0101-8292-0, Rev. C
4-12
Figure 4-11 Autobias Circuit Block Diagram
Autobias
ON In
Clock
Osc
HV OFF +
Gun OFF
HV
Is ON
Gun
ON In
Latch
AND
8 Bit
D/A
Scal ing
Amplifier
8 Bit
Up
Counter
OR
Comparator
Ref
Ref
Threshol d
IN V
AND
Analog
Switch
Analog
Switch
INV
Filament
Current
Request
To emission current
loop compensation
summing junction
Remove Clear
Clock
Remove Clear
Autobias Set
Stop
Emission
Monitor In
4.3.4 Filament Output Section
The filament output section of the FPS connects the filament power with the negative HV. The
filament power and the HV are connected to the filament by a two-conductor cable. The high
voltage (0–10 kV) from the HV Power Supply enters the FPS via J301. On standard FPS units
(PN 0620-6604-0), the high voltage is routed to the vacuum relay (K101). On such units, K101
either connects the negative HV to the secondary of the filament transformer or applies a
ground to the secondary of the filament transformer. The relay is driven from the Filament
Supply PCB via J103 pins 5 and 6.
FPS units with PN 0620-6604-0 omit the vacuum relay. On those units, the high voltage is
connected to the secondary of the filament transformer T1, which has a 10:1 ratio. The filament
transformer connects the high-voltage, low-current output of the FPS to the filament with low-
voltage, high-current filament current, superimposing the negative DC HV on the AC filament
current.
