2-32. HALF-WAVE RECTIFICATION
In producing half-wave rectified current, two valve tubes may be used. If two
valve tubes are used, (figure 2-22C), one is placed on the anode side of the x-ray tube
and the other on the cathode side. The opposing voltage then is divided across the two
valve tubes and the x-ray tube, thereby further increasing the capacity of the x-ray tube.
Hence, the use of two valve tubes increases the efficiency of the rectification system
over that of a self- rectified system. It should be noted that two-valve-tube rectifiers are
not used for full-wave rectification in radiographic equipment.
Figure 2-22. Systems of half-wave rectification.
2-33. FULL-WAVE RECTIFICATION
Full-wave rectification can be obtained by the use of a four-valve-tube rectifier
system. The valve tubes are usually placed within the transformer tank or housing and
are insulated by the oil contained in the latter. This arrangement affords protection from
x-radiation in case of faulty tube operation, and provides protection against sparkover at
the terminals of the valve tubes. The four valve tubes are connected so that the
negative half of the alternating current cycle is redirected. The rectifying action of the
four valve tubes considerably increases the capacity of an x-ray tube.
a. Figure 2-23 shows the arrangement of a four-valve-tube rectifying system
called a bridge rectifier. For one given impulse, the current (indicated by the solid
arrows) passes from the lower end of the secondary winding (negative polarity) of the
transformer, through valve tube number one, through the x-ray tube, and finally through
valve tube No.4 to the other end (positive polarity) of the transformer. When the
transformer current is reversed during the next half-cycle, the current (indicated by
broken arrows) passes from the upper end of the transformer, through valve tube
number two, to the x-ray tube, and finally through valve tube number three to reach the
opposite end of the transformer. In this way, both halves of each cycle of AC are
applied to the x-ray tube for the production of x-rays.