An x-ray generator is the device that supplies electric power to the x-ray tube.

1. x-ray
GENERATORS
Presented by: Dr. Alma swathi dsouza
Moderator: Dr. Mahesh Mijar

2. generators
An x-ray generator is the device that supplies electric power to
the x-ray tube.

3. ● An x-ray generator begins with a source of
electrical energy
● modifies this energy to meet the needs of the x-ray
tube.

4. The tube requires electrical energy for two
purposes:
1. To boil electrons from filament
2. accelerate these electrons from the cathode to the
anode.

5. The x-ray generator has a circuit for each of
these functions
filament circuit
high-voltage circuits
timer mechanism

6. The x-ray generator in two components
1.a control panel or console
2.transformer assembly

8. ● Control panels may be very simple or quite complex
● The controls allow the operator to select the appropriate kVp,
mA, and exposure time for a particular radiographic
examination

9. ● One exposure button (standby)
readies the x-ray tube for exposure
by heating the filament and rotating
the anode
● other button starts the exposure
● The timing mechanism terminates
the exposure.

10. the transformer assembly
● It contains a low-voltage transformer for the filament circuit
high-voltage transformer high-voltage circuit.
group of rectifiers
The potential differences in these circuits may be as high as 150,000
V, so the transformers and rectifiers are immersed in oil.

11. transformer assembly

12. A transformer is a device that either increases or decreases
the voltage in a circuit
Incoming Power supply- 230 V, 60 hz AC.
Filament heating requires- 10 V
Electron acceleration requires- b/w 4000 and 150000 V
So transformers are used to change the voltage of incoming power
supply to appropriate levels.
TRANSFORMER

13. potential and potential
difference.
● excess of electrons has a negative potential
● deficiency of electrons has a positive potential.
● measured in volts
● electrons will tend to flow toward the positive potential.
● This flow of electrons represents a current, and is produced by a
potential difference.
● A voltmeter is used to measure the potential difference between two
points

14. It consists of two wire coils wrapped around a
closed core

15. Core- made of tightly clamped thin sheets of
special iron alloys separated from each other by thin insulating layers-
to prevent eddy currents.

16. WORKING OF TRANSFORMER
PRINCIPLE:
When current flows through the primary coil , it creates a
magnetic field within the core, and this magnetic field
induces a current in the secondary coil.

20. Current only flows through the secondary circuit
when the magnetic field is changing (either
increasing or decreasing)
no secondary current flows while the magnetic field
in the core is in a steady state.

22. So steady DC (from a battery) cannot be used .
AC is used for transformers because it is produced by a potential
difference that changes continuously in magnitude and polarity.
So it produces a continuously changing magnetic field in the core.
AC in primary coil AC in secondary coil

23. LAWS OF TRANSFORMERS
1. The voltage in two circuits is proportional to the number of turns in the two
coils.
Np, Ns = No. of turns in primary and secondary coil
Vp, Vs = Voltage in primary and secondary coil
NP VP
----- = -----
NS VS

24. Step down Transformer
No primary coils > No secondary coils. Primary voltage > Secondary voltage

27. Step up Transformer
No. primary coils < No. secondary coils. Primary voltage < Secondary voltage

30. LAWS OF TRANSFORMERS
Vp Ip =Vs Is
2. The product of voltage and current in two circuits must be equal.
Vp, Vs - voltage in primary and secondary coil
Ip, Is - current in primary and secondary coil
Restatement of law of conservation of energy.
A transformer cannot create energy. An increase in voltage
must be accompanied by a corresponding decrease in current.

46. Filament circuit

47. Filament circuit- regulates the current flow through filament of x-ray
tube.
-It contains a step-down transformer - FILAMENT
TRANSFORMER - provides power to heat the filament.
- Current flow of 3-5 A and voltage of 10 V- sufficient
to heat the filament to necessary high temperature to
cause emission of electrons (thermionic emission).

49. Precise control of filament heating is critical because a small variation in
filament current results in large variation in x-ray tube current.
EX: 5% change in filament voltage causes 20-30 % change in x-ray tube
current.
Done by adding resistors in the filament circuit.

50. RECTIFICATION:
Process of changing AC DC
Device that produces the change - RECTIFIER.
RECTIFIERS:
Allow current to flow in only one direction.
Xray tube is a rectifier because current will not flow from anode to cathode

51. High voltage rectifiers can be-
1. Vacuum-tube type- obsolete now
2. Solid-state type-
Present in most of modern day generators
Heart of a solid state rectifier is a semiconductor

52. Semiconductor
usually a piece of crystalline silicon
Silicon contains four valence electrons
In a solid, such as silicon, there are numerous
energy levels permissible for electrons.
The valence electrons must lose or gain energy to
move from one energy level to another.

53. At absolute zero temperature, the semiconductor behaves as an
insulator.
At room temperature, some of the electrons are thermally raised to the
conduction band and are available to support a current.

54. N-type Semiconductors.
Silicon contains four valence electrons. If a material with
five valence electrons is added as an impurity to the
silicon lattice
the added atoms will take the place of some silicon atoms
throughout the crystal.
The most commonly used donor materials are arsenic and
antimony,

55. P-type Semiconductors
If an impurity with only three valence electrons is
added to silicon, the impurity atom will have only
three electrons to share with four surrounding
silicon atoms.
One silicon atom now has an electron that is
looking for another electron with which to form a
covalent bond. The absence of this electron is
called a "hole.
The P-type impurities used in semiconductors are
indium, gallium, and aluminum.

56. P-N junction
N -type and P-type crystals are joined, a P-N junction is
created.
The N type material is rich in electrons and the P-type is
rich in holes
When the junction is formed, electrons diffuse across the
junction
This creates what is called a "depletion layer.

57. Halfwave rectifier

58. Full wave rectifier

59. Full wave rectifier

60. Disadvantages of pulsed radiation

61. TYPES OF GENERATORS: THREE PHASE
GENERATORS
Three-phase generators produce an almost constant potential difference
across the x-ray tube
Commercial electric power is usually produced and delivered by three-phase
alternating-current generators

62. three basic types of 3 phase generators
Six pulse, six-rectifier
Six pulse, twelve-rectifier
Twelve-pulse

63. Three-Phase Transformers
three sets of primary and secondary windings
primary or secondary are connected in one of two configuration
delta wye (also called star).

64. Six-Pulse, Six Rectifier
This design employs a delta-wound primary transformer with a
wye-wound secondary transformer.
The output of the secondary windings is rectified with six solid-
state rectifiers.

66. Six-Pulse Twelve-Rectifier
one delta primary
two wye secondaries
12 rectifiers

67. Twelve-Pulse generators
similar to the six-pulse twelve-rectifier
transformer but secondary is not a double
wye connection; it is a wye and a delta
connection

68. Ripple factor
variation in the voltage across the x-ray tube expressed as a percentage of the
maximum value

69. Advantages of 3 phase generators over 1
phase.
Produce a nearly constant potential with very low ripple
factor
Produce x-rays efficiently throughout exposure (1 phase-
pulsed radiation)
Decrease time for exposure

70. Power Storage Generators
Used in mobile x-ray machines.
Provide a means of supplying power for the x-ray tube
independent of an external power supply
two types of power storage generators:
1. Capacitor discharge generators
2. Battery-powered generators

71. Medium-Frequency Generators
principle of high-frequency current to produce an almost
constant potential voltage

73. ADVANTAGES
Supply a constant, nearly ripple-free
voltage to x- ray tube.
More efficient and small size-
convenient for portable units and can
be integrated with x-ray tube housing.

74. ● An x-ray generator supplies electrical energy to the x-ray tube
● requires two sources of energy, one to heat the filament and the other to
accelerate electrons between the cathode and anode.
● The filament circuit
● The cathode-anode circuit, called the high-voltage circuit, contains an
autotransformer and a step-up transformer.
● The autotransformer serves as the kVp selector.
● The incoming electrical supply to the xray generator has an alternating
potential.
● Rectifiers are devices (usually silicon diodes) that transmit a current in only
one direction.
Summary

75. thank you