Power supply for x-ray apparatus

July 26, 1966

Η. T. BOEKER

3,263,151

ROWER SUPPLY FOR X-RAY APPARATUS

Filed July 2, 1962 ^EP

I

2E_DC ^EC2

0^Es 0

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3¼ Ve '3

A TRIGGER ON

,. ., SRC 66

B TRIGGER ON

SRC 64

CHARGE AND DISCHARGE

OF CAPACITOR 74 ®p-L· er

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Sheets-Sheet 1

FIG. I

FIG.4

VOLTAGE ON CAPACITOR 18

VOLTAGE ACROSS WINDING 57

VOLTAGE AT -BASE 16

VOLTAGE ACROSS WINDING 55

X-RAY TUBE ’CURRENT PULSE

VOLTAGE ON “CAPACITOR 36

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^2Edc

VOLTAGE — ACROSS WINDING 124 ^EC2 0 / CHARGE E / DISCHARGE OF CAPACITOR — 134

A TRIGGERS SCR 128 “B TRIGGERS SCR 130

1*11 tl—*1 IIa II

ABA

2_____A A

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VOLTAGE ACROSS “PRIMARY 31 /A CURRENT PULSE THROUGH PRIMARY 31 ^EPI o-

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/ \ / \ / VOLTAGE \----/---\----/— ACROSS

V V” ®5 . \ / \ / \ VOLTAGE ACROSS ξ 7 V 7 WINDING 33 '2

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FIG. 2

X-RAY TUBE CURRENT PULSE ^eP2 οχ ^ES

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VOLTAGE -ACROSS

WINDING 122

X-RAT TUBE CURRENT

PULSE

INVENTOR.

HAROLD T. BOEKER

FIG.6

ATTORNEY

July 26, 1966

Η. T. BOEKER

3,263,151

POWER SUPPLY FOR X-RAY APPARATUS

Filed July 2, 1962

Sheets-Sheet 2

<img file="US3263151A_D0010.tif" />

192

138

139

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140

72-A

FIG.5

VARIABLE D.C. SUPPLY + EDC 136

VARIABLE FREQUENCY — OSCILLATOR Π 145

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128

126

144

169

149

150

INVENTOR.

HAROLD T. BOEKER

132-i

120

146

<img file="US3263151A_D0013.tif" />

ATTORNEY

United States Patent Office

3,263,151

Patented July 26, 1966

3,263,151

POWER SUPPLY FOR X-RAY APPARATUS Harold T. Boeker, Brookfield, Wis., assignor to General

Electric Company, a corporation of New York Filed July 2,1962, Ser. No. 206,989

Claims. (CI. 321—45)

This invention relates to power supplies. More particularly, it relates to an improved power supply for X-ray apparatus.

' In X-ray equipment, it has been 'found that when a resonant transformer is utilized, the advantage is presented in that no iron core is needed to carry the magnetic flux through the transformer coils and the space normally taken up by the iron core is occupied by the X-ray tube. With such arrangement, there is enabled the convenient connecting of the accelerating sections of the X-ray tube into the secondary winding of the transformer at desired voltage levels. The X-ray tube, disposed in the center of the transformer coils, consequently, is subjected only to an axial voltage stress along its length since the transformer coils function as an electrostatic shield between the X-ray tube and the walls of the tank in which the tube and transformer are contained.

Another advantage resulting from the use of a resonant transformer in X-ray equipment is that it is possible to shape the transformer to approximate a hemisphere within a hemisphere or a cylinder within a cylinder thereby providing an optimum configuration of ultrahigh voltage application.

A further advantage is that the wave shape of the voltage from a resonant transformer is quite good when the transformer is loaded with the direct current component of the X-ray tube. In contrast, an iron core transformer produces a distorted wave shape when it is loaded down with a comparable direct current load. The wave shape generated in the secondary winding of a resonant transformer is not dependent upon the wave shape of the power applied to its primary winding. For example, the power applied to the primary winding may be in the form of pulses on both half cycles or on either of the half cycles, and a sinusoidal voltage wave is still generated in the secondary winding.

Heretofore, the weight and size of the power rectifier and power drive for a resonant transformer have, of necessity, been extremely large. A typical size for the housing for such components may be four and one-half feet by two feet by six feet and may weigh as much as one thousand pounds.

It is, accordingly, an important object of this invention to provide a power supply for an end-grounded resonant transformer conveniently utilizable in high voltage X-ray equipment whereby a substantial saving in weight and volume is effected.

It is another object to provide a power supply in accordance with the preceding object which comprises solid state devices thereby effecting substantial economy in maintenance and replacement requirements.

Generally speaking and in accordance with the invention, there is provided in combination with a unidirectional potential source and an end-grounded transformer having primary and secondary elements; gate controlled rectifying means and storage means in circuit with the primary element and the source, an oscillator and means for applying the output of the oscillator as gating signals to the gate controlled rectifying means to render the latter conductive, the storage means thereby discharging through the primary element and the rectifying means.

The novel features, which are believed to be characteristic of this invention, are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompany drawings.

In the drawings, FIG. 1 is a schematic depiction of an illustrative embodiment of the invention;

FIG. 2 is a timing diagram of waveforms occurring at different points in the circuit of FIG. 1;

FIG. 3 is a schematic diagram of a second illustrative embodiment of the invention;

FIG. 4 is a timing diagram of waveforms occurring at different points in the circuit of FIG. 3;

FIG. 5 is a schematic showing of a third illustrative embodiment of the invention; and

FIG. 6 is a timing diagram of waveforms occurring at different points in the circuit of FIG. 5.

Referring now to FIG. 1, a unidirectional potential from a source 20 is applied across the series arrangement of a variable resistor 22 and a capacitor 18, one end of capacitor 18 being grounded. The junction 19 of resistor 22 and capacitor 18 is connected to the emitter 12 of a unijunction transistor 10, a base 14 of transistor 10 being connected to source 20 through a resistor 24 and a base 16 of transistor 10 being connected to ground through a resistor 26.

A silicon controlled rectifier 28 has its cathode connected to ground and its anode connected to a terminal of the primary winding 31 of a resonant transformer 30. The output appearing at base 16 is applied to the gate electrode of silicon controlled rectifier 10.

The other terminal of primary winding 31 is connected to the junction 35 of the series arrangement of an inductor 34 and a capacitor 36, inductor 34 being connected to a source of unidirectional potential 32, capacitor 36 being connected to ground.

The secondary winding 33 of transformer 30 has one terminal thereof connected to ground through a capacitor 38 and through an ammeter 40 in shunt with capacitor 38 and its other terminal connected to the filament of the X-ray tube of an X-ray apparatus 42 through a variable resistor 44. Secondary winding 33 is tapped at various points to provide potential to the anode electrodes of the X-ray apparatus.

In considering the operation of the circuit of FIG. 1 reference is also made to FIG. 2 wherein there is shown a timing diagram of the waveforms appearing at different points of the circuit of FIG. 1.

In such operation, when undirectional positive potential is applied to junction point 35, capacitor 36 changes through inductor 34, the voltage appearing across capacitor 36 being designated as e₃. Simultaneously, capacitor 18 charges through variable resistor 22, the voltage appearing thereacross being designated e,. When the voltage across capacitor 18 reaches a given value, designated as e_p, unijunction transistor 10 is rendered conductive whereby capacitor 18 discharges into the gate electrode of silicon controlled rectifier 28 through emitter 12 and base 16 of transistor 10, the pulse of voltage appearing across resistor 26 during this discharge being designated e₂.

In FIG. 2, it is seen in the line designated e_x that when the voltage across capacitor 18 attains the value of e_p at times t, and t₂, the voltage pulses, e₂ are generated.

This voltage pulse, e₂, developed across resistor 26 during the discharge of capacitor 18, is applied to the gate electrode of silicon controlled rectifier 28 to consequently render it conductive. Such rendering causes capacitor 36 to discharge to ground through primary winding 31 and silicon controlled rectifier 28. Line e₃ in FIG. 2 shows the voltage waveform across capacitor 36, capacitor 36 being fully discharged at time i₂.

3,263,151

The inductance of primary winding 31 and capacitor 36 form a resonant circuit for the discharge of the energy stored in capacitor 36. Line e₄ of FIG. 2 shows the waveform of the voltage on primary winding 31. The current flowing through primary winding 31 and silicon controlled 5 rectifier 28 follows a damped oscillation curve as shown in line ίχ of FIG. 2. When this current starts to swing negative, silicon controlled rectifier 28 is restored to its blocking state and capacitor 36 commences to recharge. At time t_:1, unijunction transistor 10 is again rendered jq conductive and the same events are repeated. The dotted portions in line ίχ in FIG. 2 indicate that current does not flow then due to the blocking state of silicon controlled rectifier 28. Line e₅ of FIG. 2 shows the waveform of the voltage e_s in secondary winding 33. Line i₂ of FIG. la 2 shows the waveform of the current pulses through the X-ray tube.

The phasing of primary winding 31 is chosen such that the current pulse through primary winding 31 occurs during the same time that the X-ray tube conducts. The 20 repetition frequency of the pulses produced from unijunction transistor 10 is chosen to be a few cycles greater than the frequency of the resonant circuit comprising secondary winding 33 and its distributed capacitor to tank 36 to insure proper commutation of silicon controlled recti- 25 fier from the conductive to the nonconductive state.

In FIG. 1, capacitor 38 functions as a filter and the target is schematically shown and designated by the numeral 44.

In FIG. 3 wherein there is shown a second illustrative 30 embodiment in accordance with the principles of the invention, the X-ray tube in X-ray apparatus 50 comprises a filament 52 connected in series arrangement with a variable resistor 54 for controlling the voltage applied thereto from a portion of the secondary winding 57 of a 35 resonant transformer 56. The accelerating electrodes of the X-ray tube are connected to various points on secondary winding 57, one end of secondary winding 57 being grounded on the housing of the X-ray apparatus.

The primary winding 55 of transformer 56 has one ⁴⁰terminal thereof connected to the cathode of a silicon controlled rectifier 64 and its other terminal connected to the anode of a silicon controlled rectifier 66. The anode of silicon controlled rectifier 64 is connected to a variable positive D.C. supply source 68 through an in- ⁴® ductor 70 and its cathode is connected to a negative D.C. supply source 72 through a capacitor 74. The cathode of silicon controlled rectifier 66 is connected to source 72.

A voltage divider comprising a resistor 76 and a Zener diode 78 is connected between the positive and negative ⁵θ terminals of a D.C. voltage supply source 80, the regulated voltage appearing at junction 77 being the voltage supply for a variable frequency oscillator 82. The output of oscillator 82 is developed across the primary windings 83 and 87 of transformers 84 and 88 respectively. ⁵⁵

A transistor 90 has its emitter 92 connected to junction 77, its base 94 connected to junction 77 through the secondary winding 85 of transformer 84 and its collector connected to negative source 72 through the primary winding 97 of a transformer 98. A transistor 102 has its ®θ emitter 104 directly connected to junction 77, its base 106 connected to junction 77 through the secondary winding 89 of transformer 88 and its collector 108 connected to negative source 72 through the primary winding 103 of a transformer 104. ⁶®

The secondary winding 99 of transformer 98 is connected between the cathode and gate electrode of silicon controlled rectifier 64 and the secondary winding 105 of transformer 104 is connected between the cathode and gate electrode of silicon controlled rectifier 66. ⁷θ

In considering the operation of the arrangement of FIG. 3, reference is also made to FIG. 4 which is a timing diagram of the voltages appearing at various points in the circuit of FIG. 3.

In the operation of the circuit of FIG. 3, Zener diode 78 ⁷³ regulates the D.C. voltage supplied to oscillator 82. The’ output of oscillator 82 is fed to transistors 90 and 102, such output being displaced in phase by means of secondary windings 85 and 89 of transformers 84 and 88 respectively. Transformers 98 and 104 are suitably chosen to be of the pulse transformer type and secondary windings 99 and 105 thereof couple the outputs of transistors 90 and 102 to the gate electrodes of silicon controlled rectifiers 64 and 66 respectively.

When silicon controlled rectifier 64 is rendered conductive, current flows from source 68 through inductor 70 and silicon controlled rectifier 64 to charge capacitor 74. The waveform designated E_c2 in FIG. 4 shows that capacitor 74 charges during the interval between time ίχ and time t₂. When the current through the oscillator circuit formed by inductor 70 and capacitor 74 starts to reverse, the silicon controlled rectifier 64 is restored to its blocking state thereby isolating' the discharge loop comprising charged capacitor 74, primary winding 55 and silicon controlled rectifier 66 from source 68.

Line T in FIG. 4 shows the alternately occurring pulse outputs from primary windings 97 and 103 of transformers 98 and 104 respectively. It is seen that when a pulse from transistor 90 is applied to silicon controlled rectifier 64 at time ίχ, capacitor 74 has zero value of voltage.

Now, at time t₃, the output pulse from transistor 102 is applied to the gate electrode of silicon controlled rectifier 66 thereby rendering it conductive. This event permits capacitor 74 to discharge through primary winding 55 and silicon controlled rectifier 66 to source 72. The energy in capacitor 74 is dissipated in primary winding 55 and silicon controlled rectifier 66 reverts to its blocking state before the next trigger pulse from transistor 90 renders silicon controlled rectifier 64 conductive at time t₅.

Line E_p of FIG. 4 shows the waveform of the voltage in primary winding 55; line E_s shows the waveform of the voltage in secondary winding 57 and line I shows the waveform of the current pulse through the X-ray tube.

Primary winding 55 is phased such that capacitor 74 discharges therethrough during the half cycle that the X-ray tube is conductive. The frequency of the output of oscillator 82 is chosen to be at least a few cycles greater than the frequency of resonant transformer 56 to insure proper commutation of silicon controlled rectifiers from the conducting to the nonconducting state. Stage 60 schematically depicts an ammeter and th’e target is designated by numeral 62.

Resonant transformer 56 may suitably be of the type disclosed in U.S. Patent 2,144,518 to W. F. Westendorp, issued January 17, 1939, and assigned to the General Electric Company. In apparatus embodying such a transformer, there is conveniently utilized an electrostatic pickup plate such as designated by the numeral 106. Such plate is a capacitor type voltage divider comprising the capacitance from the pickup plate to the tank and of the capacitor to the hemispherical shield positioned at the top of the stack of secondary coils comprising secondary winding 57. This voltage is rectified by the full wave rectifier comprising diodes 108 and 110 and indicated in the meter 113. Meter 113 can be calibrated in terms of the voltage generated in secondary winding 57. Capacitor 112 functions as a filter.

Referring now to FIG. 5 wherein there is shown a third illustrative embodiment according to the principles of the invention, the resonant transformer 120 therein comprises an end-grounded secondary winding 122 and a pair of primary windings 124 and 126 respectively.

A terminal of primary winding 126 is connected to the cathode of a silicon controlled rectifier T28, the other terminal of primary winding 126 being connected to a source of negative D.C. potential 132 through, a capacitor 134. A terminal of primary winding 124 is connected to the anode of a silicon controlled rectifier 130, its other terminal being tied to primary winding 126. The anode of silicon controlled rectifier 128 is connected to a variable

3,263, '5 positive D.C. source 136 and the cathode of silicon controlled rectifier 130 is connected to negative source 132.

A voltage divider comprising a resistor 138 and the cathode to anode path of a Zener diode 140 is connected between a source of positive potential source 142 and 5 negative source 132, the voltage appearing at junction 139 being regulated by Zener diode 140. A variable frequency oscillator 144 receives its regulated D.C. voltage supply from junction 139. The output of oscillator 144 appears across primary windings 145 and 149 of pulse jo transformers 146 and 150 respectively.

A transistor 152 has its emitter 154 directly connected to junction 139, its base connected to junction 139 through the secondary winding 147 of transformer 146 and its collector 158 connected to source 132 through the pri- 15 mary winding 159 of a pulse transformer 160. A transistor 162 has its emitter 164 directly connected to junction 139, its base 166 connected to junction 139 through the secondary winding 151 of transformer 150 and its collector 168 connected to source 132 through the primary winding 169 of a pulse, transformer 170. The secondary winding 161 of transformer 160 is connected between the cathode and gate electrodes of silicon controlled rectifier 128 and the secondary winding 171 of pulse transformer 170 is connected between the cathode and gate electrodes of silicon controlled rectifier 130.

In considering the operation of the arrangment of FIG. 5, reference is also made to FIG. 6 which is a timing diagram of the waveforms of the voltages appearing at different points in the circuit of FIG. 5.

In operation, Zener diode 140 regulates the supply voltage for variable frequency oscillator 144. The output of oscillator 144 is applied to transistors 152 and 162 through secondary windings 147 and 151 of transformers 146 and 150 respectively, 180° out of phase with each other to produce alternately occurring trigger pulses in primary windings 159 and 169 at 180° intervals as shown in line T of FIG. 6. The pulses produced in transistors 152 and 162 alternately render silicon controlled rectifiers 1.28 and 130 conductive. When silicon controlled rectifier 128 conducts, capacitor 134 charges to twice the value of source 136. The voltage across capacitor 134 is shown in FIG. 6 on line E_c2 thereof. When the voltage across capacitor 134 attains the value of twice source 136 (2E_D._C.), the current through silicon controlled rectifier 128 starts to reverse and silicon controlled rectifier 128 is restored to its blocking state thereby isolating the discharge loop comprising charged capacitor 134, primary winding 124, and silicon controlled rectifier 130 from source 136.

Now, when the pulse from transistor 162 renders silicon controlled rectifier 130 conductive, capacitor 134 discharges to negative source 132 through primary winding 124 and silicon controlled rectifier 130. The energy in capacitor 134 is dissipated in primary winding 124 and silicon controlled rectifier 130 reverts to the blocking state before the pulse from transistor 152 renders silicon controlled rectifier 120 conductive.

It is to be noted that during the time that silicon controlled rectifier 128 is conducting and capacitor 134 is charging, a pulse of energy is introduced into primary winding 126 and that when silicon controlled rectifier 130 is conducting and capacitor 134 is discharging, a pulse of energy is introducted into primary winding 124. Lines Ερ_Χ and Ep₂ in FIG. 6 show the voltage waveforms appearing in primary windings 126 and 124 respectively. Line E_s in FIG. 6 shows the voltage waveform in sec- ⁰ondary winding 122 of resonant transformer 120. Line I in FIG. 6 shows the current waveform in the X-ray tube.

The phasing of primary windings 124 and 126 is so chosen that the charging of capacitor 134 introduces a pulse of energy into resonant transformer 120 on the half cycle that X-ray tube is not conducting while the discharging of capacitor 134 introduces a pulse of energy into transformer 120 on the half cycle when the X-ray tube is conducting. Primary windings 124 and 126 are suitably wound in the same direction. Variable oscillator 144 is chosen to have an output frequency a few cycles greater than the resonant frequency of transformer 120 to induce proper commutation to nonconductivity of silicon controlled rectifiers 128 and 130.

While there have been shown particular embodiments of this invention, it will, of course, be undestood that it is not intended to be limited thereto since many modifications both in the circuit arrangements and in the instrumentalities employed therein may be made and it is therefore contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.