Basic X-Ray Circuit

•X-ray machine circuits comprise three main components:


1. A circuit for heating the filament.
2. A circuit for applying a large potential difference (high voltage) between cathode and anode to accelerate electrons.
3. A timing device to control the length of exposure.


High-voltage circuit – provides x-ray tube accelerating potential.This circuit produces a large potential difference between cathode and anode to accelerate electrons produced at the filament to high velocities. High tension transformers convert high Amp and low kV to mA and high kV.

Filament circuit – provides filament current.The tungsten filament at the cathode is the source of electrons used to produce x-rays. The number of electrons produced at the tungsten filament is dependent upon the temperature of the filament.A tungsten filament needs to be heated to at least 2200°C to emit useful numbers of electrons. Electrons are produced by thermionic emission. When a metal is heated its atoms absorb energy which allows some electrons to move a small distance from the surface of the metal. 

Voltages can be increased or decreased using “step-up” or “step-down” transformers.Mains electricity is 240 V and has to be modified to produce a high voltage across the x-ray tube head and low voltage to heat the filament. Wire coils wound around iron rings.Coils create a magnetic field within the ring

Current and voltages (V) on opposite sides (primary and secondary) of the ring are proportional to the number of “turns” (N):

VP / VS = NP / NS

Stepwise and continuous voltage adjustments can be made with autotransformers and rheostats

Voltage Rectification :-

Alternating current is used to energize x-ray tubes ,X-ray tubes are designed to operate at a polarity where the anode is positive.

Rectifiers permit current flow in only one direction.X-Ray generators provide the tube current at the required voltage for x-ray production.In a "perfect" case this would be a constant voltage, however transformers require alternating voltages to work so some means of producing a constant voltage across the x-ray tube from the rising and falling voltage produced by the high tension transformer is required.Rectifiers placed in series in HV circuit provide half-wave rectification The ripple causes corresponding but relatively higher variations in the X-ray output. It is an unwanted phenomenon in the X-ray production due to the lengthening of the exposure time and the reduction in the average kV.
Rectifiers can be arranged in a “diamond” arrangement to provide full-wave rectification – conduction during both halves of alternating (AC) voltage.Commercial electric power, the line voltage, is usually produced and delivered as three phase alternating current. The period of each single phase may be 50 or 60 Hz. The period of a 50 Hz AC has a duration of 1/50 s, or 20 ms. The three phase X ray generator transforms and rectifies this AC into a high-voltage direct current (DC) with either six or twelve forward pulses per 20 ms period. As compared to the 100% ripple factor of single-phase generators, three-phase generators dramatically reduces voltage ripple (13–25% for 3-phase 6-pulse, 3–10% for 3-phase 12-pulse).