GE AMX-II Service Manual page 169

GENERAL ELECTRIC MEDICAL SYSTEMS AMX-I X-RAY UNIT
6-978 SM A 0654E
SEC.5 INVERTERS
Schematic reference, 60 Hz, sheet 2, 500 Hz, sheet 5, Chapter 7.
For additional description of inverter circuits see the General Electric SCR Manual, Fifth Edition, Chapter
13.2.
The 60 Hz and 500 Hz inverters are alike except for the method of turning each off and on and the power
handled. The 60 Hz inverter is turned on and off by relay contacts actuated when the handswitch ROTOR
button is pressed. The 500 Hz inverter is turned on by proper gate signal to a control SCR when the hand
switch X-RAY button is pressed, and turned off by forced commutation with another SCR when the in-
tervai timer signals the end of an exposure.
The principie of operation for both inverters is as follows. Refer to the simplified circuit in Illustration
6-7. The inverter driver is providing a square wave AC signal alternately to 2CR3 and 2CR6. Therefore,
one or the other SCR gate will be positive when the inverter is turned on. Assume that 2CR3 turns on
first. Then 2CR6 will remain in a blocking condition. The current from the 120 -v supply will flow through
the upper side of transformer T1. Transformer action will produce a voltage of approximately 2 x 120 =
240 v at the anode of 2CR6 and across capacitor C. When a positive trigger pulse is applied to the gate of
SCR2, it will turn on and apply reverse bias to 2CR3 because of the action of commutating capacitor C.
Capacitor C will maintain a reverse bias across 2CR3 long enough for 2CR3 to turn off. The next positive
trigger pulse at the gate of 2CR3 will cause the circuit to revert to the original state. In- this manner the
current from the DC supply will flow alternately through the two sides of the transformer primary and
produce an AC voltage in the secondary.
Rectifiers 2CR4 and 2CR5 feedback to the battery reactive power stored in the load at the end of a half
cycle of AC voltage.
6-10