CA1211501A

CA1211501A - High voltage power supply

Info

Publication number: CA1211501A
Application number: CA000457918A
Authority: CA
Inventors: Kenneth M. Young; Arthur P. Ruitberg
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1983-07-06
Filing date: 1984-06-29
Publication date: 1986-09-16
Also published as: JPS6051460A; EP0134167B1; US4517472A; DE3471429D1; EP0134167A3; AU567166B2; IL72086A; AU2895584A; EP0134167A2; IL72086A0

Abstract

HIGH VOLTAGE POWER SUPPLY

Abstract A high voltage power supply is formed by three discrete circuits (12, 14, 16) energized by a battery (18) to provide a plurality of concurrent output signals floating at a high output voltage on the order of several tens of kilovolts. Each circuit has a regulator stage (20, 28, 36). In the first two circuits, the regulator stages are pulse width modulated and include adjustable resistances (R1, R2) for varying the duty cycles of pulse trains provided to corresponding oscillator stages while the third regulator stage includes an adjustable resistance (R3) for varying the amplitude of a steady signal provided to a third oscillator stage. In the first circuit, the oscillator (22), formed by a constant current drive network and a tuned resonant network including a step-up transformer (46), is coupled to a second step-up transformer (24) which, in turn, supplies an amplified sinusoidal signal to a parallel pair of complementary poled rectifying, voltage multiplier stages (76, 76') to generate the high output voltage. Each of the other two circuits include oscillator drive stages (30, 38) which, together with isolation transformers (32, 40) provide output signals floating at the high output voltage.

Description

~iIGI~ VOYAGE. O'ER PLY
Technical Ill this inventioll relates to electrical vower supplies and, more particularly, to a power supply for providing a plurality of high voltage output signals.
Background Art High voltage power supplies have typically been Low frequency networks characterized principally by their mass, bulk and relative inefficiency. Recent advances in such fields as diagnostic x-ray devices (e.g., the Low Intensity X-ray and amour Imaging Device disclosed in US. Patent 4,14~,101~ have established a demand for portable battery driven power supplies able to deliver a plurality of regulated, static output voltages on the order of tens of kilowatts for periods of several hours. The operational characteristics of such devices usually require that each potential furnished my a power supply be separately adjustable.
Currently available battery operated power supplies typically have a push-pull inventor stage coupled across a center tapped primary winding of a saturable core step-up transformer. When the core saturates, a potential is induced in a second winding which causes the inventor stage to reverse its mode of conduction. The frequency of operation of the inventor stage is principally controlled by the saturation time of the transformer. Often in such configurations, a feed-back potential is derived from a secondary winding and applied to control the amplitude of the voltage applied by the inventor stage to the transformer. A voltage multiplier stage driven by another secondary winding is used in such configurations to provide an increased output voltage Jo while a voltage divider stage converts the output from the multiplier stay into a plurality of different output signals.
The use of voltage induced in the secondary winding as practiced by these prior art power supplies for switching the conduction mole of the inventor stage causes the output current provided by the transformer's secondary winding to be generated as a series of square waves pulsing at the sane frequency at which the inventor is hying switched.
In effect, such power supplies rely upon the transformer to establish the switching frequency of the inventor siege, harmonics of the switching frequency are, there-fore, included in any signal appearing across the secondary windings of the transformer. The presence of such harmonics introduces substantial undesired ripple into -the output signals provided by the power supply.
Moreover, the use of a divider stage to provide multiple output signals prevents independent adjustment of the output potentials. Furthermore, the presence of high current spikes occurrillg luring changes in core saturation and the sudden change in the amplitude of current which occurs at each transition between pulses causes a reflected ripple current which, in turn, causes electromagnetic noise that detrimentally interferes with the operation of any neighboring electrical equipment. Also, the saturable core of the transformer is a significant source of energy loss, a factor which renders these configurations unsuitable for use in battery powered, high potential supply sources. the presence of such ripple renters this type of power supply unsuitable far use in applications where both a constant high voltage and a well regulate but much lower amplitude voltage floating at the high voltage are required as output signals because the ripple from the high voltage stage destroys the regulation ox the low voltage stage.
Attempts to improve the regulation of output potentials have included efforts to compensate for variations in output voltages due to causes such as changes in loading. Such efforts typically rely upon a pulse width modulator to regulate a chopping transistor driving the center tap of the primary winding. In these configurations a feedback loop, such as a current sensing stage is often used to provide an analog signal for controlling the duty cycle of the modulator in proportion to charges in the loading of the transformer's secondary winding.
Lo This type of power supply is not suitable for providing high voltages, however, because of a lack of electrical insulation between the input and output sides of the circuit. Moreover, such power supplies require synchronization between the pulse width modulator and the transformer, a feature which restricts the range over which the duty cycle of the modulator may be varied to compensate for changes in loading of the power supply.
Other power supplies have attempted to obtain well regulated output signals by using a separate control circuit having ancillary oscillator and base drive stages to regulate switching of transistors driving a transformer in a power converting stage.
Tile ancillary circuits themselves require a power supply. the presence of such ancillary circuits and their individual power supply undesirably adds to the complexity and physical bulk of the overall design.
Moreover, the control circuit in such power supplies is driven by a feedback signal obtained directly from the output terminals of the power supply, a feature which prevents insulation of the control circuit from the output voltages and, therefore, renders these power supplies unsuitable for generatic)r1 of Hayakawa output volts Recent efforts to enable a power supply to provide high voltages suitable for operation o-f x-ray tubes have included a variety of capacitive discharge circuits. one power supply, for example, included a motor riven rotating commutator providing sequent trial discharge of individual capacitors through the lo primary winding of a step-up tranformerO Although capacitive discharge type power supplies are adequate for providing high voltage impulses of short dune-lion, without extensive, power consuming filtering, the transient phenomenon accompanying discharge renders such power supplies unsuitable for providing well regulated output voltages. Additionally, the presence of motor driven, rotating commutators makes such power supplies less than ideal for use in small, portable devices.
Statement of Invention Accordingly, it is an object of the present invention to provide an improved high voltage power supply.
It is another object to provide a power supply able to continuously furnish a well regulated output potential on the order of tens of kilovolts.
It is a further object to provide a battery powered power supply able to continuously furnish a well regulated output potential on the order of tens of kilovolts.
It is yet another object to provide a power supply providing a plurality of independently adjustable, high voltage output potentials.
It is also an object to provide a power supply providing a plurality of well regulated, high voltage outputs.

it is a still furtlrer o~)jcct to ~rovidc .
I Lo rye Lowry Lye COlltinUOl~sLy fUrtlisll a wet I rug to Ol:t~Ut potential on the order of tens of kilovolts.
These and other objects are achieved with a high voltage power supply having a plurality of circuits coupled in parallel between an unidirectional energy source and a common output terminal, and providing a plurality of concurrent output signals. Two of the circuits include modulated regulator stages driving corresponding oscillator stages with pulse trains having particular repetition rates. A third one of the circuits has a regulator stage controlling the flow of energy between the energy source and a third oscillator stage. Each of the oscillator stages includes a transformer forming part of a tuned network and providing a sinusoidal signal at the frequency of the tuned network across secondary windings coupled on one side to the common output terminal. One of the first two circuits also includes a step-up transformer supplying an amplified corresponding one of the sinusoidal signals to a parallel pair of complementary poled rectifying, voltage multiplier stages which, in turn, provide a unidirectional output voltage having an amplitude on the order of several tens of kilovolts between the common output terminal and a network reference. The sinusoidal signal provided by the second of the two circuits floats at the amplitude of the underquote-I tonal output voltage while the third circuit includes a rectifier stage converting the corresponding sinusoidal signal into a unidirectional signal having an amplitude varying slightly from that of the unidirectional output voltage.

grief ~)escri~tioll ox tile rules __ _ Figure L is u ~I.oclc di~lyr~lll Sue (Ill ~'m~OC]illlC'nt of the present inverltioll arrange to provide power to a typical load.
Logger 2 is an electrical schematic diagram of a high voltage circuit included in the embodiment of Figure 1.
Figures PA through EYE illustrate waveforms of signals occurring at several points t'nrougholit the I high voltage circuit Shirley in figure 2.
inure 4 is an electrical schematic diagram of a second circuit included in the embodiment of Figure 1.
Figure 5 is an electrical schematic diagram of a third circuit included in the embodiment of Figure 1.
D_ tied Description of the Invention Refer now to the drawings and, in particular, to Figure 1 which illustrates the interconnections between the various stages of a power supply for providing several indeperldently adjustable output potentials to such devices as a triodes type x-ray tube 10. The power supply is -formed by three multistate circuits 12, 14, 16 coupled in parallel between a direct current source such as a battery 18, and a common output terminal Pi.
Circuit 12 includes a switching regulator stage 20 having its input coupled across battery 18 for driving a sine wave oscillator 22. An adjustable resistance, such as a rheostat, R1 is included in regulator stage 20 to adjust its duty cycle. The output of oscillator 22 it applied across a primary winding of a step-up isolation transformer 24. A
secondary winding of transformer 24 is coupled across a voltage multiplier 26 which furnishes a negative potential difference on the order of several tens of kilovolts between output terminals Lo Pi. Output terminal Pi is common to all three circuits while I

terminal Pi is connected to a reference potential such as a network ground.
Circuit 14 has a switching regulator stage 28 coupled across battery 18 and a rheostat R2 providing adjustment of its duty cycle. Regulator stage 28 provides power to a push-pull drive stage 30 which, in turn, has its output applied across a primary winding of an isolation transformer 32 which, in turn, develops an alternating voltage on its secondary winding One side of the second defy winding of transformer 32 is coupled to common output terminal Pi while the other side thereof forms output terminal Pi.
Circuit 16 includes a linear regulator stage 36 coupled across battery 18 for providing power to oscillator drive stage 38. Regulator stage 36 operates as a linear resistance which consumes power from oscillator 38 to con trot the amplitude of generated signals in response to variations in output voltage sensed by the regulator. As adjustable resistance R3 is provided for the regulator.
The output of drive stage 38 is applied across a primary winding of an isolation transformer 40. A secondary winding of transformer 40 has one leg coupled to common output terminal Pi and its other leg coupled to terminal Pi This winding develops an output signal which is rectified by a diode Do and filtered by a capacitance Of to provide a low amplitude direct voltage between terminals Pi and Pi.
Transformers 24, 32 and 40 are compact, high voltage isolation transformers which are disclosed in our US.
Patent 4,510,476 issued April Thea, 1985.
In the power supply of Figure 1, circuit 12 is designed to provide a well regulated voltage having I., an amplitude on tile order of severely tens of kilovolt (yo-yo., TV t~l~tW~ I 1, while tilt other cir(l~its I I no Dyson t-, provide output signals at voltages differing from the voltage occurring between terminals Pi, Pi by less titan one kilovolt. In the exemplary application shown, terminals Pi, Pi are connected to establish a potential difference between a filament 34 and an anode 44 of x-ray tube 10. Output terminals Pi anal I are coupled across filament 34 while terminal Pi is coupled to a grid 42 of x-ray tube 10. The commonality of output terminal Pi to all three circuits assures that output signals provided by circuits 14, 16 float at a high voltage near the level of the constant potential difference between terminals Pi, Pi. Consequently, the signal applied to filament 34 by circuit 14 has a direct current potential of several tens of kilovolts (e.g., -80 TV) with respect to terminal Pi. The power supply also applies a direct voltage to grid 42 which has an amplitude varying between the sum and difference of the high voltage appearing between terminals Pi, Pi and the potential supplied by circuit 16 between the terminals Pi, Pi. The potential difference between terminals Pi, Pi is designed to be slightly more negative (e.g., 80 to 150 volts) than the potential applied across filament 34 to enable grid 42 to repel and thereby focus electrons emitted by filament 34 into a stream directed toward anode 44, thus causing anode 44 to emit an x-ray beam 45. Anode 44 is coupled to the network reference potential.
Figure 2 illustrates in detail the several stases of high voltage circuit 12. Regulator stage 20 is formed with a pulse width modulating regulator Ml, such as a commercially available sixteen pin SO 1524 Jo integrated circuit chip manufacture by Silicon General Comparly. Resistance R4 Ann capacitance C~2 are eoup.Le(l l~c~een torts no 7 or regulator Ml a a reference potential, to establish the inter~ml pulse repetition frequency, if, of regulator stage 20. Adjustable resistance Al, in conjunction with fixed resistances R5, RUG, form a voltage divider establishing an adjustable reference voltage (across resistances R5 and Al) and a fixed reference voltage (across resistance R6) to ports 2 and 16, respectively, of regulator Ml for establishing the duty cycle of regulator Ml. Power is supplied directly to regulator stage 20 via input terminal Pi to port 15 of regulator Ml and to the remainder of circuit 12 via the emitter and collector electrodes of a transistor Al. The base of transistor Al is biased by resistances R7, R8 and connected, via resistance R7, to output ports 12, 13 of regulator Ml. This enables regulator Ml to establish the bias voltage applied to the base of transistor Al and thereby control whether transistor Q1 is in a conducting or a non-conducting mode so that while regulator Ml is in one state of its duty cycle, transistor Al is held in a conducting mode, thereby allowing current to flow from terminal Pi to the center taps Pi, Pi of primary windings We, We, respectively, of a step-up transformer 46 via the emitter and collector electrodes. While regulator Ml is in the other state of its duty cycle, the bias voltage applied by regulator Ml to the base of transistor Q1 holds the transistor in a non-conducting mode, thereby interrupting the flow of current between terminal Pi and transformer 46. The width and the frequency of the pulses are controlled by the duty cycle and frequency, Fly respectively, of regulator Ml. The waveform of the train of voltage pulses appeari~lc3 at Lowe Pi is shown in figure I With a battery I providirl(3 a (irk:
voltage of about fifteen volts to terminal Pi, and regulator ill set to operate with a duty cycle of about fifty percent the average voltage appearing at node Pi will be approximately seven and one-half volts.
A constant current sine wave oscillator 22 is formed by transformer 46, a pair of transistors Q2, Q3 coupled in a push-pull configuration between the two center tapped windings We, We of transformer 46, and inductance Lo. Inductance Lo is coupled between the collector electrode of transistor Al and center tap Pi of primary winding We. The energy stored in inductance Lo maintains a continuous current flow through winding We while transistor Al is held in a non-conductinc3 mode. The waveform shown in Figure 3B
represents the amplitude of current flowing through inductance Lo. The base electrodes of transistors Q2, Q3 are coupled across winding I Bias voltages are applied to the base electrodes by the two sections of winding We through a potential applied to center tap Pi from current flowing from node Pi, through a series of resistances Al R11 and a diode Do which restricts the current flow through a series of resistances R10, Roll and a diode Do which restricts the current flow through center tap Pi to a single direction. During each cycle of the oscillator, one of transistors Q2, Q3 is held in a non-conducting mode by the amplitude of the potential applied to its base electrode while the other transistor is held in a conducting mode with current flowing through inductance Lo and across its collector and emitter electrodes via center tap Pi I and a corresponding section of winding We, and througil the collector and emitter junction of either transistor Q2 or Q3. Resistance R12 establishes a potential between the coupled emitter electrodes of transistors I Q3 and the network reference potential for current sensing while a diode Do assures a constant current flow through inductance Lo when transistor Al is in a conducting mode.
A capacitance C3 is coupled across primary winding We while a capacitance I is coupled across a secondary winding We. Together, capacitances C3, C4 and transformer 46 form an equivalent tuned resonant circuit which establishes a resonant frequency, F2, for oscillator stage 22. As represented by Figures 3C and ED, the amplitudes of voltages appearing across the collector electrodes of transistors Q2, Q3, respectively, each have half cycle sinusoidal waveforms with a frequency equal to f2. The turns ratio between windings We and We is selected to provide a step-up in the voltage across winding We.
A turns ratio of about 1 14.5, for example, will provide a peak-to-peak voltage across winding We of approximately one hundred and ten volts.
Switching between the conducting and non-conducting modes of transistors Q2, Q3 occurs at twice the resonant frequency f2 it once every one-ha].f cycle) established by capacitors C3, C4 and transformer 46, and is implemented by the bias voltages applied by winding We to the base electrodes of each of the transistors. Voltages induced across winding We exhibit the same sinusoidal waveform (albeit with smiler amplitudes) as voltages occurring across the collector electrodes. Windings We and We are wound in a flux additive direction Consequently, as the voltage on one collector electrode of transistors I Q3 falls to Nero due to cycling of the equivalent resonant circuit, a reversal of current occurs through winding We, I

thereby causing simultaneous shifts in tune bias voltages induced across winding We applied to the base electrodes. These shifts cause the transistor which has a minimum collector voltage to be biased in a conducting mode during a one-half cycle while the other transistor is biased in a non-conducting mode.
Assuming, for purposes of explanation, that voltage on the collector of transistor I reaches a minimum at time t , as is shown in Figure ED, then the simultaneous shift in the bias voltages places transistor Q3 into its conduction mode and, for one-half of a cycle, allows current to flow through inductance I one part of winding We, across the collector and emitter electrodes of transistor Q3, and through resistance R12 to the network reference potential. The amplitude of current flowing through the collector electrode of transistor Q3 is represented by the waveform shown in Figure YE.
Capacitance C5 is coupled between resistances ~10, Roll and the network reference potential to provide filtering of transient currents caused by the transition of transistor Al between its conducting and non-conducting modes.
Transformer 24 exhibits a high degree of leakage current due to a large number of closely spaced turns in its primary and secondary windings. A capacitance C6 is serially connected between the network rev-erroneous potential and one end of primary winding We of transformer 24 to provide series tuning with the leakage inductance and thereby assure that at the oscillator frequency, the series combination of the leakage inductance and capacitance C6 form an equivalent zero net impedance.
Figure OF represents the sinusoidal alternating voltage applied by secondary winding I of trueness former 46 to primary winding I of transformer 24. A sinusoidal alternating voltage of higher amplitude, represented by the waveform shown in Figure 3G, is developed by transformer action across secondary winding We. Transformer 24 (to he discussed in greater detail hereinafter) is designed to provide across winding We a substantial voltage increase over the voltage applied across winding We.
A turns ratio of approximately 1:92, for example, will produce a peak-to-peak voltage of about ten kilovolts between terminals Pit, Ploy Secondary winding We is connected across voltage multiplier 26 which is formed by a complementary pair of oppositely poled, high order voltage multiplier stages 76, 76'. Each of these stages has five cascaded units formed by pairs of capacitances C7 and diodes Do. One side of each one of multiplication stages 76, 76' are coupled together, in parallel, across terminals P10, Pit of secondary winding We.
The diodes Do in each stage 76, 76' are arranged with opposite polarities, thereby causing the stages to exhibit opposite polarities, thus assuring that the net potential across the two multiplier stages are substantially equal and additive. Together, the ten units of parallel multiplication stages I 76' provide full wave rectification, a high degree of filtering, and an approximately eight-fold increase in the peak-to-peak potential across terminals Pit, P10 of secondary winding We. Accordingly, a ten kilovolt difference across terminals Pit, Pro will result in a constant forty kilovolt difference across terminals Pit and Pi and a constant eighty kilovolt difference across terminals Pi, Pi. Figure 31-l represents the waveform of the potential difference between terminals Pi, Pi. A resistance R13 provides a low value load to limit excessive current flow in the event that terminal Pi becomes short circuited to I

the network reference potential. anal thereby protect the multiplier stage from dc-lm~l~e. Lowe cleaved arCillq or corona (due to causes Swiss as humility) between individual. components in multiplier 26 or between multiplier 26 and transformer 24, both multiplier 26 and transformer are potted in a compound having a high breakdown strength such as Canopy Nell, a co~pond commercially available from the Canopy Company, which has a breakdown strength of approximately six hundred volts per mill 'transformer 46 also has a winding ~10 with a center tap P12 connected to tune network reference potential. A pair of diodes Do, Do are coupled with common cathodes to opposite ends of winding Wow between center tap P12 and a junction P13 to provide full wave rectification of signals developed across winding Wow. The voltage amplitude of those signals varies in response to changes in the voltage developed between terminals P10, Pit and is used, therefore, to provide a feedback signal for governing the duty cycle of regulator Ml set by resistance Al. The feedback signal is taken from terminal P13 and applied via a current limiting resistance R14 directly to port 1 of regulator lo and, via filters formed by a resistance R15 coupled in parallel with a capacitance C8, and by a capacitance C9 serially coupled to a resistance R16, to ports 9 and 16 of regulator Ml. A change in the voltage developed between terminals P10, Pit is reflected by transformers 24, 26 in the amplitude of the voltage occurring across winding Wow which, in turn, causes a change in the amplitude of current in the feedback signal applied via resistance R14 to regulator Ml. The feedback signal applied directly to one port of regulator Ml effectively creates an offset voltage to a constant five volt signal supplied my port 16 of regulator Ml; Tao offset voltage varies linearly with changes in the feedback signal. The potential difference between the reference signal and the -feedback signal applied to port 9 of regulator Ml is amplified internally by regulator Ml, thereby enabling regulator Ml to automatically respond to changes in the voltage across terminals P10, P11 as those changes are reflected back to winding Wow, by internally varying the length of its duty cycle, thus causing a corresponding change in the average amplitude of the signal applied to center tap Pi and, ultimately, in the voltage developed across terminals Pi, Pi.
The feedback voltage occurring at terminal P13 is 15 also applied directly to the anode of a ever diode Do and, via resistances R20, R21, to bias the base electrode of a transistor Q4. The cathode of diode Do is coupled, via the emitter electrode of transistor Q4 and a resistance R22, to the gate 20 electrode of silicon controlled rectifier Do, and, via a resistance R23, to the network reference potential. voltage between node P13 and the emitter electrode of transistor Q4 which exceeds the zoner voltage (i.e., an over-voltage) of diode Do 25 will drive the diode into a reverse conduction mode thereby causing a drop in the potential across the collector and emitter electrodes of transistor Q4.
This drop, in urn, causes a drop in the voltage on the gate electrode of zoner diode I thereby 30 latching diode Do into conduction and effectively shunting the base drive of transistors Q2, Q3 to the network reference potential. Consequently, transistors Q2, Q3 are held in a non conduction mode, thus preventing operation of the oscillator stage and 35 consequential failure of circuit 12 due to such causes as, for example, the occurrence of a short I

I

circuit condition bitterly terminals Pi, I thereby providing short circuit protection for (circuit 12. A
capacitance C10 in parallel with a resistance R24 forms a filter connected between the gate electrode of rectifier Do and the network reference potential to prevent transient voltages such as those due to electromagnetic interference, from controlling the gate electrode.
As shown in Figure 4, circuit 14 also includes a pulse width modulated regulator My (which also may be a sixteen pin SO 1524 integrated circuit chip) having a port 15 coupled directly to terminal transistor Q5 and between terminal Pi and output ports 12, 13 of regulator My, thereby enabling regulator My to establish the bias voltage applied to the base electrode for switching the transistor between conducting and non-conducting modes according to the state of the duty cycle of regulator My. Connection of the base electrode to output ports 12, 13 of regulator My enables the regulator to adjust the modulation of transistor Q5 over a range between approximately five and ninety-five percent of a cycle. A resistance R32 and a capacitance C20 are coupled between ports 6, 7 of regulator My to establish the operational frequency, f3, of regulator stage 28. Adjustable resistance R2, together with resistances R33, R34, form a voltage divider establishing an adjustable reference voltage (across resistance R34) to ports 2, 16 of regulator My for establishirlg its duty cycle.
Transistor Q5 is, in effect, a chopper similar in its application to transistor Al in circuit 12, driven by regulator My to convert the direct current applied to terminal Pi into a continuous train of direct current pulses applied via node P22 to an inductance Lo in push-pull drive stage 30. Current flowing through inductance Lo is ~pplie(l to a center tap P21 of prowler wir~dillg We of: slop p isc)l.lti~lrl transforln(~r 32. I sightliness C22 is coupled across both ends of winding We to form a tuned resonant circuit Together, capacitance C22 and transformer 32 form an equivalent resonant circuit which serves as a constant current oscillator Whitehall a resonant frequency f4.
Current flow through the center tap of winding We and alternately (dependillg upon the instantaneous state of the resonant circuit) through each section of winding We and the corresponding collector and emitter electrodes of a pair of transistors Q6, Q7 coupled in a push-pull configuration across opposite ends of winding We. A pair of zoner diodes D10, Dull are coupled across the collector and emitter electrodes of transistors Q6, Q7, respectively, to protect -them against transient spikes during switching. The base electrodes of transistors Q6, Q7 are coupled across a winding Wow of transformer 32.
Bias voltages are applied to the base electrodes by two sections of winding Wow through a potential applied to center tap P23 from a current flowing from node P22~ through a series resistance R36 and a capacitor C23 having one side connected to the network reference potential. A resistance R37 connects center tap P23 to a node P24 between resistance R36 and capacitance C23. Current flowing through primary winding We induces a current in winding Wow by transformer action. During each cycle of the oscillator, one of transistors QG, Q7 is held in a non-conducting mode by the bias potential applied to its base electrode by the corresponding section of winding Wow while the other transistor is held in a conducting mode with current flowing through inductance Lo and across its collector and -1~3-emitter electrodes via center tap P23 all a corresponding Sexual of win(iirl(3 We. resistance R3 establishes a potential between Lowe killed errantry electrodes of transistors Q6, Q7 and the network reference potential while a diode D12 assures a unidirectional current flow through inductance Lo when -transistor Q5 is in a conducting mode. A ratio of about 6:5 between the turns of primary and secondary windings We, We will provide a sinusoidal output signal across terminals Pi, Pi having a peak-to-peak amplitude of between zero and two volts, depending upon the duty cycle of regulator My established by the setting of resistance R2.
Transformer 32 has a third winding Wow wound in the same direction as windings We end Wow, with a center tap P24 coupled directly to the network reference potential. A pair of diodes D13, D14 with common cathodes are coupled to opposite section of winding Wow between center tap P24 and a resistance R39 to provide full wave rectification of signals developed across winding Wow. The voltage amplitude of these signals varies in response to changes in the output potential developed between terminals Pi, Pi and is used to provide a feedback signal applied directly to port 1 of regulator My and, across a capacitance C24, to port 9 of regulator My. The voltage developed between the feedback and reference signals is amplified and compared by an amplifier and error detection stage internal to regulator My, to the mixed reference voltage provided by resistance ~34. Variations between the amplified feedback signal and the fixed reference voltage are applied by circuitry internal to regulator My to automatically control its duty cycle and thereby regulate the amplitude of the voltage developed across output terminals Pi, Pi. A resistance R40, coupled in parallel White a zoner icky 1)15 bow no i~tarlce 1~39 Allah tile ductwork reL(rtl~ce Lyle l (I vow amp1ltll(le of the fce(1h(~ck swigger Lo across;
winding lo to a level compatible with the operational characteristics of regulator My. The amplitudes of voltages appearing across both collector electrodes of transistors Q6 Q7 have sinusoidal waveforms with a frequency equal to f4.
The turns ratio between windings We and I is lo selected to provide an output voltage between output terminals Pi Pi having a variation in amplitude of approximately two volts zero-to-peak.
As shown in Figure 5 circuit 16 includes a regulator stage 36 having a linear voltacJe regulator My such Claus a sixteen pin SO 1532 integrated circuit chip manufactured by Silicon General Company. Power is applied directly to ports VOW 8 of regulator My via terminal Pi. Regulator My has output ports l 7 coupled to nodes P26 P27 and a voltage divider formed by serially connected resistances R42, R3 and R43. In effect regulator stage 36 operates a variable impedance to dissipate a small amount of power which would otherwise he applied to oscillator 38. An adjustable reference voltage developed at a node P28 between adjustable resistance R3 and resistance R43 is applied to control port 2 of regulator My to enable its internal error detection circuitry to provide adjustment of the voltage supplied by regulator My at its port l to node P26.
A capacitance C26 coupled between ports 5, 9 and a resistance R44 coupled between ports 3 4 establish reference potentials for the internal error detection circuitry of regulator My. A resistance R45 coupled between node P26 and ports 6 lo enables internal current limiting circuitry of regulator My to automatically adjust tune voltage on terminal P26 in response to changes in current flow through terminal P26.
Drive stage pa includes a transistor Qg couple between regulator 36 and transformer 40 to serve as a chopper to periodically interrupt current flow between regulator 36 and transformer 40. Regulator My provides a substantially constant voltage via node P25 to -the collector electrode of transistor Q9. A
bias potential is applied to the base electrode of transistor Q9 by a resistance R46 serially coupled with a capacitance C27 between the base electrode and node P27. The emitter electrode is connected via diode D16 to a node P29. large capacitance C28, coupled in parallel with primary winding We of transformer 40, between node P29 and the network reference potential, forms a circuit having a resonant frequency f5. The emitter electrode is also connected to one side of a winding Wow which is oppositely poled to that of winding We; the other side of winding Wow is connected to resistance R46.
A resistance ~48 is coupled between the collector and base electrode to provide sufficient voltage to bias transistor Q9 into a conducting mode to provide for cyclical recharging of capacitance C28 to its peak resorlanee voltage. During operation, current flows cyclically in alternate directions between eapaeitanee Kiwi and winding We. When the voltage across eapaeitanee C28 roaches a peak value, the voltage induced in winding ~14 provides a base bias voltage for transistor I through resistance R46 and capacitor C27 to enable current to flow between the collector and emitter electrodes.
When the voltage across capacitance C28 falls to a minimum at the end of each half cycle, the polarity of current through winding Wow causes the bias voltage on the base electrode to hold the collector and emitter electrodes in a nonconducting state, thereby permitting current flowing from winding We to recharge capacitance C28 to its peak voltage. In effect, oscil-later 38 and transformer 40 form a Hartley o~cillatorproviding a sinusoidal output signal across winding We.
With a step-up turns ratio of 1:12.S between windings We and We, and a constant potential of fifteen volts applied between terminal Pi and the network reference potential, circuit 16 provides a half-wave rectified voltage between output terminals Pi, Pi having an amply-tune which may be varied by adjusting resistance R3~
between approximately eighty and one hundred and fifty volts. The amount of ripple occurring between terminals Pi, Pi is principally due to the half-wave rectification.
Maintenance of the high voltage between terminals Pi, Pi limits the amount of the ripple occurring on terminal Pi to less than one percent of the voltage occurring between terminals Pi, Pi.
The construction of transformers 24, 32 and 40 is generally described in the afore-identified US. Patent 4,510,4760 As constructed, these transformers are compact, have low loss closed coxes To To, To respectively, made of a magnetic material such as a ceramic ferrite, and electrically isolate the several tens of kilovolts applied between output terminal Pi and the network reference potential from the other stages of circuits 14, 16. The primary winding We of transformer 24 is wound around an annular spool insulator Al and secondary winding We is wound around a similar insulator Blue as shown in Figure 1. In transformer 32 9 windings We, Wow and Wow are wound in the same direction around spool insulator A

.,~

and secondary winding We is wound around insulator By, wile in transformer 40 windings I and Wow are wound in opposite directions on insulator A and winding We is wound on insulator By. Spool insulators Al, A, A, I By and By have axial boxes lined with discrete coatings So of an electrically conducting material exhibiting a lower electrical conductivity than the conductors of which the transformer windings are made. The spool insulators are mounted upon opposite legs of their respective transformer cores.
innings We, We, Wow, Wow, We, We, Wow, and We are each encased in simian, but discrete coatings of the electrically conducting material: coating So encases primary winding We; coating So encases windings We, Wow and Wow; coating So encases secondary winding We; coating So encases windings ~5 and ~14; and coating So encases winding I Coatings So through So are in intimate adhesive contact with the underlying surfaces of the corresponding insulating spools; coatings So through So also completely encase and thus physically separate the respective windings from the other parts of transformers 24, 32, 40.
As shown in Figure 2, a lead Al in transformer 24 extending from coating So lining the axial bore of insulator I couples coating So to core To and terminal Pro while a lead X2 couples coating So to terminal Pi. As shown in Figure 4, in transformer 30 32, a lead X3 couples coating So to center tap P21 and a lead X4 couples coating So to terminal Pi. As shown in Figure 5, in transformer 40, a lead X5 couples coating So to one side of winding We and the network reference potential while a lead X6 couples coating So to terminal Pit. A lead X7 couples coatings So lining the axial bores of insulators A, By to core To and terminal ~?10, while a Learn Yea couples coax go So lining tile axial ices of insulators I Lo to core To and terlni~al P10. The connections between coatings So through So and the corresponding encased windings assure -that any potential differences between the windings and their respective coatings are minimized in amplitude, thereby avoiding sparking between the windings and their coatings. The coupling between coatings Sly the corresponding cores To, To, To, and terminal P10 eliminates the possibility of sparking within the axial bores of the insulating spools while maintaining a potential difference between the cores and to network reference potential which is approximately one-half of the potential. difference between the corresponding primary and secondary windings.
The power supply disclosed is suitable for construction as a very compact, light weight, efficient network which may be continuously powered for several hours by a stall direct current source such as a dry cell battery. One battery powered embodiment, for example, drew approximately eight watts of power and, exclusive of the battery, was able to be housed in a container of about one hundred and twenty eight cubic inches. Moreover, by having regulator stages 20, 28 operated at frequencies on the order of fifty to sixty kilohertz to drive oscillators having resonant frequencies on the order of fifteen to thirty kilo-Hertz (i.e., the ratio between pulse repetition frequency in a regulator stage and the corresponding oscillator may be between

2:1 and 10:1), the network is able to rely upon the oscillators to attenuate haromic frequencies of signals generated by the regulator stages and thereby provide well regulated output signals without requiring substantial filter stages, Furthermore the use of two, parallel voltage multiplier stages coupled across a step-up transformer provides on extremely large multiplication of the potential difference applied across the transformer with a minimal number of components and a concomitant saving of power.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A high voltage power supply providing a plurality of concurrent output signals, comprising:
input terminal means for providing energization potential from a undirectional source;
output terminal means for providing a common reference for each of the plurality of concurrent output signals;
a first voltage generating circuit comprising:
first oscillator circuit means having a first tuned network including first transformer means, for developing a first sinusoidal signal at the resonant frequency of said first tuned network, first regulator circuit means for developing pulses at a particular repetition rate and duty cycle, for con-trolling the amplitude of said sinusoidal signal by inter-rupting the flow of energization potential to said first oscillator circuit means from said input terminal means, second transformer means for significantly in-creasing the amplitude of said sinusoidal signal, and voltage multiplier and rectifier circuit means including a second output terminal, coupled to said second transformer means for developing a unidirectional output voltage of several tens of kilovolts amplitude across said common output terminal means and said second output terminal;
a second voltage generating circuit comprising:
second oscillator circuit means having a second tuned network including a third output terminal and third transformer means for developing a second sinusoidal signal at the resonant frequency of said second tuned net-work floating at said unidirectional output voltage across said common output terminal means and said third output terminal, second regulator circuit means for developing pulses at a particular repetition rate and duty cycle for controlling the amplitude of said second sinusoidal signal by interrupting the flow of energizing potential to said second oscillator circuit means from said input terminal means; and a third voltage generating circuit comprising:
third oscillator circuit means having a third tuned network including fourth transformer means, for developing a third sinusoidal signal at the resonant frequency of said third tuned network, third regulator circuit means for controlling the amplitude of said third sinusoidal signal by varying the magnitude of the flow of energizing potential from said input terminal means to said third oscillator circuit means, and rectifier circuit means for converting said third sinusoidal signal into a unidirectional output signal of an amplitude varying slightly from that of said unidirectional output voltage across said common first output terminal means and a fourth output terminal.

2. The power supply of claim 1 wherein the pulse repetition rate of each of said first and second regulator circuit means is at least twice the resonant frequency of each of said tuned networks of their respective voltage generating circuits.

3. The power supply of claim 2 wherein each of said first and second oscillator circuit means comprises a push pull constant current oscillator.

4. The power supply of claim 2 wherein each of said first and second regulator circuit means includes means for individually establishing the particular duty cycle of the pulses developed by each of said first and second regulator circuit means.

5. The power supply of claim 2 wherein each of said first and second regulator circuit means comprises a switching type regulator.

6. The power supply of claim 2 wherein said third regulator circuit means comprises a linear impedance type regulator.

7. The power supply of claim 2 wherein each of said first, third and fourth transformer means includes a single secondary winding and at least one primary winding coupled across a capacitive reactance to form respective ones of said tuned networks.

8. The power supply of claim 7 wherein at least said third and fourth transformer means are constructed to exhibit a significantly high electrical insulation between their primary and secondary windings.

9. The power supply of claim 2 wherein said voltage multiplier and rectifier circuit means comprise comple-mentary pairs of multiple units of diodes and capacitors and said complementary pairs are parallel coupled across said common output terminal means and said second output terminal.

10. The power supply of claim 2 wherein each of said first, second and third voltage generating circuits further comprises circuit means which include a sense winding on each of said second, third and fourth trans-former means for providing a feedback signal indicative of a variation in the amplitude of the output voltage across the output terminals of each of said voltage generating circuits to adjust the operation of each of said first, second and third regulator circuit means thereby to vary the amplitude of the sinusoidal signal developed by each of said oscillator circuit means.

11. The power supply of claim 10 wherein said first voltage generating circuit further comprises circuit means to which the feedback signal is applied for ter-minating the development of a sinusoidal signal by said first oscillator circuit means in response to a sub-stantial load current drain across the output terminals of said first voltage generating circuit.

12. A high voltage power supply providing a plural-ity of concurrent high voltage output signals, comprising:
a first circuit having a pair of input ports con-nectable across a source of electrical energy, comprising:
first regulating means coupled to said input ports and having a first intermediate terminal, for inverting said electrical energy into a first train of pulses characterized by a first pulse frequency and a first average amplitude, said first regulating means including first means for varying said first average amplitude;
first oscillator means including a first resonant circuit exhibiting a first resonant frequency connected to said first intermediate terminal, for transforming said first train of pulses into a first sinusoidal signal having a peak-to-peak amplitude exceeding said first average amplitude;
first transformer means having a primary winding coupled to receive said first sinusoidal signal, and a secondary winding, for amplifying said first sinusoidal signal; and first and second rectifying means having opposite polarities and collectively providing a common terminal and a reference terminal, additively coupled in parallel across said secondary winding of said first transformer means for rectifying said amplified first sinusoidal signal and for multiplying the amplitude of said second sinusoidal signal to provide a substantially constant high voltage signal across said first pair of output terminals;
a second circuit having a pair of input ports con-nectable across said source, comprising:

second regulating means coupled to said input ports and having a second intermediate terminal, for inverting said electrical energy into a second train of pulses characterized by a second pulse frequency and a second average amplitude, said second regulating means including second means for varying said second average amplitude;
second oscillator means including: second trans-former means having a secondary winding providing at one end a first output terminal and coupled at its other end to said common terminal and a center-tapped primary winding, for inducing a second sinusoidal signal across said secondary winding; first reactive means coupled across said primary winding to form a second resonant circuit with said second transformer means; second reactive means coupled between said second intermediate terminal and said center tap; and first switching means having a pair of alternately conducting switching devices connected between said second intermediate terminal and different ends of said primary winding for cyclically providing paths of current flow from alternate of said different ends of said primary winding; a third circuit having a pair of input ports connectable across said source, comprising:
third regulating means interposed between said input ports and an intermediate terminal for providing an intermediate potential difference between said inter-mediate terminal and said reference terminal, said third regulating means including third means for varying the amplitude of said intermediate potential difference;
second oscillator means including: third trans-former means having a second winding and a primary winding for inducing an alternating signal across said secondary winding; third reactive means coupled across said primary winding to form a third resonant circuit with said third transformer means; and switching means coupled to said intermediate terminal for cyclically coupling said intermediate terminal to one end of said primary winding; and means providing at one end a second output terminal and coupled at its other end to said common terminal, for converting said alternating signal into an output signal having an amplitude varying from the amplitude of said high voltage signal between said reference terminal and said second output terminal.

13. The power supply of claim 12 wherein said second and third transformer means comprise:
core means each including pairs of legs, for concentrating lines of magnetic flux in ferromagnetic paths within said core means;
a plurality of electrically insulating means each encircling different ones of said legs;
a first and equal plurality of coatings of an electrically conducting material exhibiting a first electrical conductivity completely covering the surface areas of different ones of said insulating means adjacent to said core means; and means for interconnecting said core means and said first plurality of coatings to one side of said secondary winding of said first transformer means.

14. The power supply of claim 13 wherein said pri-mary and said secondary windings of said second and third transformer means have a second and greater elec-trical conductivity and are wound around different ones of said insulating means to generate a magnetic flux in corresponding ones of said core means, further comprising a second plurality of coatings of said electrically conducting material for separating and completely surround-ing different ones of said primary and secondary windings and lining the surface areas of corresponding ones of said insulating means adjacent to said windings.

15. The power supply of claim 14 wherein each of said second plurality of coatings are separately coupled to corresponding ones of said primary and secondary windings.

16. A high voltage power supply providing a plural-ity of concurrent output signals, comprising:
first and second regulator stages each having a pair of input ports connectable across a source of electrical energy, each providing a separate intermediate terminal, each inverting said electrical energy into separate trains of pulses characterized by average ampli-tudes and respective first and second operational fre-quencies, and each of said regulator stages including separate impedance means for independently varying the duty cycle of a corresponding one of said regulator stages and thereby changing said average amplitude of the cor-responding one of said trains of pulses;
first and second oscillator stages each including respective ones of a first and second reactive impedance separately coupled to corresponding ones of said inter-mediate terminals, first and second transformer means each having a secondary winding and a primary winding having a center tap connected to said corresponding ones of said intermediate terminals via one of said first and second reactive impedances for inducing first and second sinusoidal signals across corresponding ones of said secondary windings, third and fourth reactive im-pedances forming first and second resonant circuits exhibiting respective first and second resonant fre-quencies with respective ones of said transformer means, said first and second operational frequencies being greater in value than corresponding of said first and second resonant frequencies, and first and second switch-ing means having a pair of alternately conducting switch-ing devices connected between said intermediate terminal and different ends of a corresponding one of said primary windings;
third transformer means having a secondary winding and a primary winding, coupled to said first transformer means and providing a step-up relation to said secondary winding, for transforming said first sinusoidal signal into a third sinusoidal signal;
first and second complementary voltage multiplier stages additively coupled in parallel across said secon-dary winding of said third transformer means, having a common terminal and a reference terminal forming a first pair of output terminals, and providing an output voltage having an amplitude on the order of several tens of kilo-volts at said common terminal, said common terminal being coupled to one side of said secondary winding of said second transformer means;
a third regulator stage having a pair of input ports connectable across said source of electrical energy and providing an intermediate potential difference, said third regulator stage including means for varying the amplitude of said intermediate potential difference;
third oscillator stage including fourth trans-former means having a primary and a secondary winding, a fifth reactive impedance forming a third resonant circuit with said fourth transformer means, and third switching means connected to said third resonant circuit coupled between said third regulator stage and said third resonant circuit for cyclically applying said intermediate potential difference to said third resonant circuit; one side of said secondary winding of said fourth transformer means being connected to said common terminal;
said second and fourth transformer means having cores of magnetic material electrically coupled to one side of said secondary winding of said third trans-former means; and means coupled to said secondary winding of said fourth transformer means for converting a signal occur-ring across said secondary winding into an output signal having an amplitude differing from the amplitude of said output voltage.

17. The power supply of claim 16 wherein said first and second operational frequencies are greater than respective ones of said first and second resonant fre-quencies by at least a factor of two.

18. The power supply of claim 17, further com-prising circuit means which include a sense winding, on each of said first, second and fourth transformer means for providing a feedback signal indicative of a variation in the amplitude of the output voltage across said secondary windings of each of said first, second and fourth transformer means to adjust the operation of each of said first, second and third regulator stages and thereby vary the amplitude of the sinusoidal signal developed by each of said oscillator stages.

33.