Figure 2-23. Full-wave rectification. Alternating current (solid and broken
arrows pointing in opposite directions). Full-wave pulsating direct
current (solid and broken arrows pointing in the same direction).
b. In essence, a full-wave rectification circuit is nothing more than a switching
network that always keeps the cathode of the x-ray tube connected to the negative side
of the transformer and the anode connected to the positive side.
(1) In recent years, valve tubes have been replaced by solid state and
contact rectifiers in most of the new equipment. Silicon and other semiconductor
materials, as well as stacked selenium rectifiers, are now available that will withstand
the high voltages used in producing x-radiation. These devices have some distinct
advantages over valve tubes.
(2) For example, they do not require filament supply transformers and
operate much cooler without a heated filament. In addition, they have a lower forward
resistance which results in a lower voltage drop across the rectifier. This means less
power loss in the high voltage circuit. These rectifiers can be used to replace the valve
tubes in older equipment; however, the high voltage circuit would have to be completely
2-34. METHOD OF TESTING RECTIFIERS AND TIMERS
If one of the rectifiers in a full-wave bridge rectifier circuit is not working, the mA
will be below normal. The spinning-top test (figure 2-24) may be used to establish the
operation of the rectifiers.