GE AMX-II

GENERAL ELECTRIC MEDICAL SYSTEMS AMX-li X-RAY UNIT
7-1576 SM AO654E
SEC.6 X-RAY TUBE FILAMENT SUPPLY AND CONTROL CIRCUITS
Schematic reference sheet 6, Chapter 7.
1.
Filament circuit adjustment requires (a) filament voltage near as possible to the proper amount re-
quired to give 100 ma without regulator action and (b) compensation adjustments that will permit
the regulator to hold ma constant as the battery voltage changes over its operating range (it dips as
low as 90 v during an exposure).
Tube ma is controlled by voltage at the filament transformer 7T2 (Illustration 6-8). This voitage
is applied by the proper firing of CR16 and CR20.
As the tube current flows through the reference branch (B1) and the signal branch (B2) voltage is
developed across R56 (V1) and R58 (V2) respectivily. When tube current is 100 ma V1 and V2 are
equal. See Illustration 6-9. If tube current varies from 100 ma V2 will vary proportionately but V1
will remain about the same. This results from the regulator action of CR59 which maintains a rela
tively constant potential across B1, forcing any current change to pass through R58.
| TUBE
CURRENT
R58
82
18791010
ILLUSTRATION 6-9
When a change in tube current causes V2 to vary, Q60 collector voltage wili change. That portion of
collector voltage picked off by R30 is applied to C22, which then takes more or less time to charge
to the turn-on voltage of Q26. When 026 turns on, C22 discharges as shown in Illustration 6-8. The
discharge pulse is transmitted by T18 to the gates of CR16 and CR20, thereby providing phase con-
trol of CR16 and CR20. Q26 is reset and C22 discharged at the end of each 500 Hz half-cycle, as
the unfiltered power supply drops to zero.
To test circuit operation, assume tube current drops below 100 ma. The decreased current will cause
V2 to drop. 060 will conduct less current causing collector voltage to rise. The increased collector
voltage will charge capacitor C22 at a faster rate resulting in quicker turn-on of Q26. The earlier dis-
charge pulses will fire CR 16 and CR17 earlier during each power pulse increasing filament voltage
and tube current. The opposite will occur if tube current rises above 100 ma.
The ma regulator will correct a 5 to 20% error in ma within 20 to 40 ms after an exposure starts.
Examples of ma regulation are shown in W-31A.
During the 2-1/2 sec. warm up period the X-ray tube filament is heated to a preset temperature in
the manner shown in Illustration 6-10.
6-13