CA1101562A - Image tube power supply - Google Patents
Image tube power supplyInfo
- Publication number
- CA1101562A CA1101562A CA268,827A CA268827A CA1101562A CA 1101562 A CA1101562 A CA 1101562A CA 268827 A CA268827 A CA 268827A CA 1101562 A CA1101562 A CA 1101562A
- Authority
- CA
- Canada
- Prior art keywords
- power
- tube
- oscillator
- coupled
- voltage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5383—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a self-oscillating arrangement
- H02M7/53838—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a self-oscillating arrangement using a single commutation path
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/338—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only in a self-oscillating arrangement
- H02M3/3381—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only in a self-oscillating arrangement using a single commutation path
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
- H02M7/10—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode arranged for operation in series, e.g. for multiplication of voltage
- H02M7/103—Containing passive elements (capacitively coupled) which are ordered in cascade on one source
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
- H02M1/007—Plural converter units in cascade
Abstract
Alan W. Hoover - 2 IMAGE TUBE POWER SUPPLY
Abstract of the Disclosure This power supply detects the total power input to an image tube of the type utilizing microchannel plate electron multipliers in order to set the image output brightness. A current sensing resistor in the oscillator circuit provides a feedback potential in proportion to the total power demand of the image tube. This potential is applied to a transistorized circuit for limiting the input to the oscillator to a predetermined level.
Abstract of the Disclosure This power supply detects the total power input to an image tube of the type utilizing microchannel plate electron multipliers in order to set the image output brightness. A current sensing resistor in the oscillator circuit provides a feedback potential in proportion to the total power demand of the image tube. This potential is applied to a transistorized circuit for limiting the input to the oscillator to a predetermined level.
Description
S~;2 Alan W. Hoover - 2 Backqrou-nd oi the Invention Power supplies for image intensifiers utilizing microchannel plate electron multipliers generally require expensive and comple~ electronic circuitrv to accommodate for variations in input light levels while maintaining the output tube brightness relatively constant. A pair of oscillators, an automatic brightness control, and three high voltage multipliers are usually required along with a standard voltage clamp for good image tube operating performance. Since these circuits contain a plurality of expensive individual components it is very difficult to keep the tolerances of these individual components within the limits necessary to assure proper total circuit oper~tion.One method for achieving constant imags tube brightness consists in detecting extremely small currents in the phosphor screen circuit. Since the variations in the phosphor screen current with changing levels of input light are very small complex circuit components are~ requlred to amplify these small current values to a useable level. The purpose of this invention therefore is to provide good image intensifier operation without the need for complex electronic circuitry generally required for image tubes containing microchannel plate electron multipliers.
Summar~of the Invention An image tube power supply utilizes a current detector element to detect changes in total tube power in relation to changes in tube input illumination.
The current changes are then refelected in the low voltage power supply circuit where they are electronically sensed. A pair af transistors are coupled with the current detector to provide \negative feedback for controlling the input volta~e to the power supply oscillator. Controlling the input oscillator voltage in turn governs the operating voltages of the individual tube components resulting in good regulation of the tube output light intensity.
Summar~of the Invention An image tube power supply utilizes a current detector element to detect changes in total tube power in relation to changes in tube input illumination.
The current changes are then refelected in the low voltage power supply circuit where they are electronically sensed. A pair af transistors are coupled with the current detector to provide \negative feedback for controlling the input volta~e to the power supply oscillator. Controlling the input oscillator voltage in turn governs the operating voltages of the individual tube components resulting in good regulation of the tube output light intensity.
- 2~
56~2 The power supply is further simplified by utilizing the briyht source pro-tection cixcuit components in combination with the microchannel plate strip resistance as a voltage divider.
The output o~ a single voltage multiplier is divided by this circuit cornbination between the voltage required for the cathode and the voltage required across the microchannel plate.
Thus, in accordance with one broad aspect of the inven-tion, there is provided a controlled brightness power supply for image tubes of the type containing a micro-channel plate electron multiplier and a phosphor screen comprising: oscillator means for providing A.C. power when coupled with a source of D.C.
power; rectifier means coupled with said oscillator for provid-ing D.C. power to the tube; power sensing means consisting of a resistive element electrically coupled in series between said D.C. power source and said oscillator for detecting changes in -tube operating power corresponding to changes in the tube input illumination and reducing the microchannel plate electron multi-plier voltage to provide a constant illumination at the phosphor screen; and control circuit means electrically coupled with the ~0 power sensor and oscillator in feed-back relation for controlling the A.C. power in response to the changes in the tube operating power consisting of at least one transistor electrically coupled between the oscillator and the D.C. power source to control the conduction through the oscillator.
In accordance with another broad aspect of the invention there is provided a controlled brightness power supply for image tubes of the type having a micro-channel plate electron multi-plier comprising; oscillator rneans for providing A.C. power when coupled with a source of D.C. power; rectifier means coupled with said oscillator for providing D.C. power to the tube;
bright source protection circuit means electrically coupled with _3_ ~,~
i6Z
the micro-channel plate and rectifier for preventing increases in tube illumination from damaging the tube cat~ode; and at least one resistor serially coupled with at least one output of said micro-channel plate for detecting changes in the tube input illumination and limiting the D.C. power to the oscillator when current through the resistor exceeds a predetermined value~ :
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-3a-,, 56~
Alan W. Hoover - 2 Brief Desc!iption of the Drawinqs Flgure 1 is a block diagram of a prlor art lmage tube power supply;
Flgure 2 is a block diagram of the lmage tube power supply oi this invention;
Figure 3 is a circuit diagram of the power supply of Figure 2;
Figure 4 is a graphic representation of the light response characteristics of an image intensifier tube employing the circuit of Figure 3;
Figure 5 is an alternate embodiment o the circuit of Figure 3; and Figure 6 is a further embodiment of the circuit of Figure 3.
Description of the Prior Art Figure 1 is a block diagram of a typlcal power supply used for image tubes containing microchannel plate electron multipliers.: The battery B
applies voltage to a Iirst oscillator regulator 3 and ~a second osclllatDr regulator 2 for converting the low input bal~tery voltage to~a high voltage A.C.at a regulated output level. The voltage level of the flrst oscillator: 3 is applied to a first multiplier 7 by means ~of lead 5, The first multipIier 7 converts the lnput A. C. voltage to an increas~d D. C. voltage~for connection to the image tube 1. The increased D. C. output of the first multiplier 7 is applied across the microchannel: plate electron multlpller 11 by means of:
leads g and 13 . The OUtpllt of the first multlplier 7 ~is also connected to theoutput of a second multiplier 6 by means of lead 24. Battery B also supplies input voltage to a second oscillator regulator 2 which provides a high voltage A.C.
to a second multiplier 6 by means oi lead~4, The high voltage D.C. output of the second multiplier 6 is referenced to the output voltage of the first multiplier 7 and is coupled with a bright source protector circuit 10 by means of lead 8.
The-bright source protector circult (BSP) 10 is a clamp circuit which maintains LS~i~
Alan W. Hoover - 2 the tube cathode potential at about 1 - 2 volts as the tube cathocle current lncreases above some preset level. This is to protect the cathode 14 at high input light levels. The cathode 14 is connected to the BSP circuit 10 by means of lead 12. The high voltage output of the second oscillator regulator 2 is also applied to the input of a third multiplier 18 by means of lead 16. The high positive D.C. output of the third multiplier 18 i5 connected to the tube phosphor screen 2? by means of lead 20. The light output occurring at the phosphor screen 22 is regulated in the following manner. A sensing resistor R
is connected to lead 24' in the ground return oi the third multiplier 18 in order to detect changes in screen current. The voltage drop across R which increases with increasing screen current is applied to the automatic brightness control circuit 17 by means oi lead 15, The automatic brightness control circuit ~ABC) 17 generally contains a field ~effect transistor in combination with four resistors, a capacitor and a diode, and operates to control the first oscillator regulator 3 by decreasing the output voltage of the first multi-plier 7 resulting in reduced voltage to the mlcrochannel plate ll to keep the screen current constant at the aforementioned pre-set level. Since the accelerating potential between the microchannel plate and the screen and the current Into the screen are both maintained at a constant level,then constant power is supplied to the screen resulting in a constant phosphor light output when the input light level is hlgh enough to activate the ABC circuit. The tube output brlghtness therefore will remain constant over a wide range of input illumination to the tube above a predetermined input illumination value, One example of a prior art power suppl~ currently used with image intensifier tubes can be seen by reference to U,S, Patent No. 3,666,947 issued to W,R,Wyess, 5~2 Alan W. Hoover - 2 Description of the Prefer ed Embodiment One embodiment of thls invention can be seen by reference to Figure 2.
Battery B is connected to a single oscillator 27 by means of leads 25, 43, and power control circuit 28 and supplies the oscillator input with a low constant D.C. voltage. The oscillator output leads 29' and 45 supply an increased A.C.
voltage to multipliers 31, 31' and 50 where the voltage is rectified and increased to a much higher value. The output of multiplier 31 is connected to the cathode 14 of image tube 1 by means of leads 33, 35, 47' and BSP circuit l0. The BSP
circuit 10 operates in a similar manner to known BSP circuits to protect the cathode against sudden current surges caused by large variations in input illu-mination to the tube 1. Coupled between the battery B and os~cillator 27 by means of leads 43, 41, 41' and 25 is a power sensor circu~t 37 and power control circuit 28, the function of which will be described in greater detail below. The outpuS~of oscillator 27 is connected to the input of multiplier 50 bymeans of lead 45, and the output of multiplier 50 is coupled to the microchannelplate 11 by means of leads 47, 49. The phosphor screen 22 is coupled to the output of a third multiplier 31 by lead 26. The input of the third multiplier 31' is connected to the output of oscillator 27 by lead 45~
In operation, the D.C. voltage derived from battery B is converted from low voltage D.C. to high voltage A.C. by means of oscillator 27. The oscillator 27 in turn drives the high voltage multipliers 31, 31' and 50 which increase thevoltage output level and con~rerts the high A. C. voltage back to D. C. at high potential. The high potential D.C. voltage is applied to the intensifier tube components to provide proper operation. When the cathode 14 is shielded from any light illumination a fixed level of input current from battery B is demanded by the power supply circuit. This current, designated as quiescent current, i5 deter-mlned chiefly by circuit losses and by the microchannel plate (dark) current demand. As light is caused to fall upon the cathode 14 and the light input level is increased, light-induced currents begin to flow in the tube 1, The S6;~
Alan W. Hoover - 2 increased current flow requires an increased power level which is reflected back through the circuit to the D,C. input of battery B. This increased power demandcan therefore be detected at any convenient point in the system and used to control the voltage applied to the tube 1. If the voltage on the tube elements, namely the cathode 14, microchannel plate 11 and phosphor screen 22, is caused to decrease as the light-induced tube current increases the tube output light level will remain relatively constant. The variation of tube output brightness A as a function of input illumination is shown in Figure 4.
Figure 3 is a detailed circuit diagram containing some of the components of the block diagram of Figure 2 and describes the operation of the power sensor circuit 37 and the power control circuit 28 in greater detail. D.C. power is ap-plied to the collector of series pass transistor Ql by connection to the positive terminal of battery ~. Current flows through Ql by connection between the emitt0r of Ql and the input to oscillator 27, ~ Osc~llator 27 consists of resistors R2, R3, capacitor Cl, transistor Q3 and transformer Tl connected together to form a class C oscillator. The power control circuit 28 consists of transistors (;~ ' Q2 and resistor Rl. Resistor R2 and capacitor Cl bias ~ransistor Q3 in the active region,and resistor R3 limits mlnimum base current in transistor Q3 and stabilizes the oscillator characteristic for variation in characteristics of transistor Q3. Capacitor C2 connected to the emitter of transistor Ql and the collector of transistor C?3, and to one side of capacitor Cl and resistor R2,provides a low A.C. source impedance to oscillator 27.
Load changes at the secondary S of transformer I'l are reflected back into the pr~mary P and can be sensed by detecting the voltage drop occurring across resistor R4 which is coupled between transformer primary P and ground.
Capacitor C3 coupled between primary P and ground serves to bypass A,C.
components occurring across R4 and should therefore have a reactance that is Alan W. Hoover - 2 low compared to the resistance value R4 at operating frequency of oscillator 27.The emitter of Q3 is connected to one side of transformer prlmary P. One side of R4 is connected to the base of transistor Q2 so that the voltage appearing across R4 is used to control the conduction through transistor Q2 which in turn control the conduction through Ql The collector of Q2 is connected to the base of Ql and the emitter of Q2 is connected to ground. This connection comprises a feedback circuit constructed in such a way as to provide negative feedback such that increasing current through R4 causes the voltage occurring across R4 to increase and the voltage applied to oscillator 27 to decrease. This in turn results in the current through R4 being maintained at a constant value. Thus the effective power sensor 37 could consist of a resistive element connected between the oscillator transformer primary and ground. The combination of the current flow through resistor R4 and the re~sulting voltage drop provide an approx-imate means for determining the effective input power requirements of the image intenslfier. ~ ~
High voltage multipliers 31 and 31' are connected~ to the output of Tl .
Multiplier 31' i9 a 12-stage multiplier which multiplies and rectifies the 500 volt output of Tl to generate +6,000 volts D.C. which is applied directly to thephosphor screen 22, Multiplier 31, oonsisting of a plurality of capacitors and diodes ln voltage doubling arrangement, increases and rectifies the 500 volts provided by transformer Tl to a -1, 000 volts D . C. level for connection to themicrochannel plate 11 and cathode 14. The bPight source protection circuit 10 comprises reslstors R5, R6, R7, R8, connected with diode Dl to form a voltage clamp for maintainlng the voltage applied tp cathode 14 at a predetermined minimum level. Resistors R6 and R7 in parallel with R8 also serve to form a voltage divider in combination with the resistance of the microchannel plate 11.This provides -800 volts across microchannel plate 11 and -200 volts on cathode 14, In order to set the overall intensifier gain level it is necessary to L5~ Alan W. Hoover - 2 ad~ust the voltage level across the microchannel plate ll, This is easily accomplished hy varying the value of resistor R8 rather than adjusting the values of both resistors R6 and R7. The utilization of the circuit components of the bright source protection circuit lO in combination with the reslstance ofmicrochannel plate ll multifunctionally provides the correct voltage for both the tube cathode 14 and microchhanel plate ll without the necessity of a third multiplier as is required with power supplies of the prior art as described earlier. Since both of these tube elements are supplied by the same multiplier 31 and oscillator 27 then the method of sensing efiective input power by means of resistor R,4 and the feedback relationship between transistors Ql and Q2 to control the input power to oscillator 27 is a very slmple method ~or controllingthe light output of tube l, The voltage multiplier provided by the combination of the resistive elements in the BSP circult lO and the resistance of the micro-channel plate ll is possible since the so-called "strip" reslstance of the micro-- 15 channel plate ll is a measured constant value. The strip res~stance for resis-tance to current ~qow provided by the integral electrical properties of the micro-channel plate materlal is typicalls7 in the order of between 106 and 101 ohms, The strip resistance depends to large extent upon the degree of activation of the microchannel plate glass when the glass is of the lead oxide type and is made conductive by treating the glass in a reducing atmosphere~ Resistance values in the order of 108 and lO9 ohms are usually employed, and these values remain relatively constant throughout the liPe of the image tube. Typicalvalues émployed Eor image tube circuits used with image tubes containing microchannel plates are 200 volts betweerl the image tube cathode and the input face of the microchannel plate, and 800 volts between the input and output faces of the microchannel plate. Since the output voltage of the voltage multi-plier 31 is typically in the order of l,000 volts, the resistance values of reslstors R5, A6, R7 and R8 of the BSP clrcuit 10 are chosen so that the voltage _ g _ ;.
s~z Alan W. Hoover - 2 appearln~ between the cathode 14 and the mlcrochannel plate 11 ls approxi-mately 200 volts and the voltage appearlng across microchannel plate 11 is approximately 800 volts when no lnput illumination is caused to fall upon the tube cathode 14.
Prior art power supplies using several oscillators and multipliers to lndividually provide operating power to the tube components generally sense the operating current of one of the tube components, such as the phosphor screen current, and control the tube operating characteristics for this component by varying the microchannel plate voltage. The power requirements of the other tube operating components is not affected. Earlier attempts to control image tube light output by simplified circuit means for monitoring one of the tube operating parameters and providing feedback control to the tube operating voltages have not been successful since the tube parameters such as photocathode current and phosphor screen current represent values in the order of nanoamps. Changes in the order of several nanoamps require complex and expensive circuitry to detect, amplify and use signals of such small value. It was unexpected therefore that changes in the total tube operating power could be useably detecSed in the input power requlrements to the power supply. It was heretofore believed that chanyes in the increasing light level to the tube cathode would have little effect on the tube operating power requirements, nor was it realized that there would be enough change in effective tube power demand with increasing light level to achieve effective control over the tube output light level. Employing constant current control on the primary side of the power supply, however, unexpectedlylprovides high light level tube saturation characteristics which are relatively constant over a five decade range of tube input light illumination Figure 5 shows an alternate arrangement for the controlled power supply of this invention. In the embodiment of Figure 5 the effective power sensing lS~iZ
Alan W. Hoover - 2 reslstor R4 ls connected between the battery B and the emltter of transistor Ql and a zener diode D2 is connected between the base of Ql and the battery B.
Resistor R1 is connected to the base of Q1, the anode of D2 and ground. In this arrangement the diode D2 functions as a reference element, Ql functions as a combined comparison and power control element, and resistor R4 senses the total current change. This clrcuit provides a constant current source independent of input light over a predetermined value of input illumination.
Figure 6 is an alternate embodiment of the circuit of Figure 3 where the effect~ve power sensor resistor R4 is coupled between the output of multi-plier 31 and yround, and capacitor C3 is coupled in parallel with resistor R4.
In this arrangement R4 senses the changes in current in both the cathode 14 and the microcha-nnel plate 11 and reflects these changes in the input circuit to oscillator 27 by connection to the base of transistor Q2 in the manner as described earlier for the power control circuit 37 of the embodiment of Figure 3~.
Although the feedback mechanism is ~described as employing transistors in various arrangements within the power control circuit, it is readily apparent that other circuit elements can be used to provide the feedback and control function. Power sensing elements in the embodiments discussed are resistive type elements which reflect a voltage dlfference in relatlon to the quantity of current transmitted through the element. Other known elements which reflect posltive volt-ampere characteristics, where the voltage increases in relation to current, can also be employed.
The use of the controlled power supply of this invention primarily finds application wlth image tubes that are used for mobile type applications such as night vision devices for military purposes and for providing vision to peoplesuffering from night blind diseases. This is in no way intended as a limitation iZ
Alan W. Hoover - 2 in scope. The controlled power supply oi this lnventLon flnds application wherever compact and lnexpensive clrcuitry is requlred for monitoring light power requirements and for controlling operational power to all type optical-electronic devlces.
RAM: ch December 30, 1975
56~2 The power supply is further simplified by utilizing the briyht source pro-tection cixcuit components in combination with the microchannel plate strip resistance as a voltage divider.
The output o~ a single voltage multiplier is divided by this circuit cornbination between the voltage required for the cathode and the voltage required across the microchannel plate.
Thus, in accordance with one broad aspect of the inven-tion, there is provided a controlled brightness power supply for image tubes of the type containing a micro-channel plate electron multiplier and a phosphor screen comprising: oscillator means for providing A.C. power when coupled with a source of D.C.
power; rectifier means coupled with said oscillator for provid-ing D.C. power to the tube; power sensing means consisting of a resistive element electrically coupled in series between said D.C. power source and said oscillator for detecting changes in -tube operating power corresponding to changes in the tube input illumination and reducing the microchannel plate electron multi-plier voltage to provide a constant illumination at the phosphor screen; and control circuit means electrically coupled with the ~0 power sensor and oscillator in feed-back relation for controlling the A.C. power in response to the changes in the tube operating power consisting of at least one transistor electrically coupled between the oscillator and the D.C. power source to control the conduction through the oscillator.
In accordance with another broad aspect of the invention there is provided a controlled brightness power supply for image tubes of the type having a micro-channel plate electron multi-plier comprising; oscillator rneans for providing A.C. power when coupled with a source of D.C. power; rectifier means coupled with said oscillator for providing D.C. power to the tube;
bright source protection circuit means electrically coupled with _3_ ~,~
i6Z
the micro-channel plate and rectifier for preventing increases in tube illumination from damaging the tube cat~ode; and at least one resistor serially coupled with at least one output of said micro-channel plate for detecting changes in the tube input illumination and limiting the D.C. power to the oscillator when current through the resistor exceeds a predetermined value~ :
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-3a-,, 56~
Alan W. Hoover - 2 Brief Desc!iption of the Drawinqs Flgure 1 is a block diagram of a prlor art lmage tube power supply;
Flgure 2 is a block diagram of the lmage tube power supply oi this invention;
Figure 3 is a circuit diagram of the power supply of Figure 2;
Figure 4 is a graphic representation of the light response characteristics of an image intensifier tube employing the circuit of Figure 3;
Figure 5 is an alternate embodiment o the circuit of Figure 3; and Figure 6 is a further embodiment of the circuit of Figure 3.
Description of the Prior Art Figure 1 is a block diagram of a typlcal power supply used for image tubes containing microchannel plate electron multipliers.: The battery B
applies voltage to a Iirst oscillator regulator 3 and ~a second osclllatDr regulator 2 for converting the low input bal~tery voltage to~a high voltage A.C.at a regulated output level. The voltage level of the flrst oscillator: 3 is applied to a first multiplier 7 by means ~of lead 5, The first multipIier 7 converts the lnput A. C. voltage to an increas~d D. C. voltage~for connection to the image tube 1. The increased D. C. output of the first multiplier 7 is applied across the microchannel: plate electron multlpller 11 by means of:
leads g and 13 . The OUtpllt of the first multlplier 7 ~is also connected to theoutput of a second multiplier 6 by means of lead 24. Battery B also supplies input voltage to a second oscillator regulator 2 which provides a high voltage A.C.
to a second multiplier 6 by means oi lead~4, The high voltage D.C. output of the second multiplier 6 is referenced to the output voltage of the first multiplier 7 and is coupled with a bright source protector circuit 10 by means of lead 8.
The-bright source protector circult (BSP) 10 is a clamp circuit which maintains LS~i~
Alan W. Hoover - 2 the tube cathode potential at about 1 - 2 volts as the tube cathocle current lncreases above some preset level. This is to protect the cathode 14 at high input light levels. The cathode 14 is connected to the BSP circuit 10 by means of lead 12. The high voltage output of the second oscillator regulator 2 is also applied to the input of a third multiplier 18 by means of lead 16. The high positive D.C. output of the third multiplier 18 i5 connected to the tube phosphor screen 2? by means of lead 20. The light output occurring at the phosphor screen 22 is regulated in the following manner. A sensing resistor R
is connected to lead 24' in the ground return oi the third multiplier 18 in order to detect changes in screen current. The voltage drop across R which increases with increasing screen current is applied to the automatic brightness control circuit 17 by means oi lead 15, The automatic brightness control circuit ~ABC) 17 generally contains a field ~effect transistor in combination with four resistors, a capacitor and a diode, and operates to control the first oscillator regulator 3 by decreasing the output voltage of the first multi-plier 7 resulting in reduced voltage to the mlcrochannel plate ll to keep the screen current constant at the aforementioned pre-set level. Since the accelerating potential between the microchannel plate and the screen and the current Into the screen are both maintained at a constant level,then constant power is supplied to the screen resulting in a constant phosphor light output when the input light level is hlgh enough to activate the ABC circuit. The tube output brlghtness therefore will remain constant over a wide range of input illumination to the tube above a predetermined input illumination value, One example of a prior art power suppl~ currently used with image intensifier tubes can be seen by reference to U,S, Patent No. 3,666,947 issued to W,R,Wyess, 5~2 Alan W. Hoover - 2 Description of the Prefer ed Embodiment One embodiment of thls invention can be seen by reference to Figure 2.
Battery B is connected to a single oscillator 27 by means of leads 25, 43, and power control circuit 28 and supplies the oscillator input with a low constant D.C. voltage. The oscillator output leads 29' and 45 supply an increased A.C.
voltage to multipliers 31, 31' and 50 where the voltage is rectified and increased to a much higher value. The output of multiplier 31 is connected to the cathode 14 of image tube 1 by means of leads 33, 35, 47' and BSP circuit l0. The BSP
circuit 10 operates in a similar manner to known BSP circuits to protect the cathode against sudden current surges caused by large variations in input illu-mination to the tube 1. Coupled between the battery B and os~cillator 27 by means of leads 43, 41, 41' and 25 is a power sensor circu~t 37 and power control circuit 28, the function of which will be described in greater detail below. The outpuS~of oscillator 27 is connected to the input of multiplier 50 bymeans of lead 45, and the output of multiplier 50 is coupled to the microchannelplate 11 by means of leads 47, 49. The phosphor screen 22 is coupled to the output of a third multiplier 31 by lead 26. The input of the third multiplier 31' is connected to the output of oscillator 27 by lead 45~
In operation, the D.C. voltage derived from battery B is converted from low voltage D.C. to high voltage A.C. by means of oscillator 27. The oscillator 27 in turn drives the high voltage multipliers 31, 31' and 50 which increase thevoltage output level and con~rerts the high A. C. voltage back to D. C. at high potential. The high potential D.C. voltage is applied to the intensifier tube components to provide proper operation. When the cathode 14 is shielded from any light illumination a fixed level of input current from battery B is demanded by the power supply circuit. This current, designated as quiescent current, i5 deter-mlned chiefly by circuit losses and by the microchannel plate (dark) current demand. As light is caused to fall upon the cathode 14 and the light input level is increased, light-induced currents begin to flow in the tube 1, The S6;~
Alan W. Hoover - 2 increased current flow requires an increased power level which is reflected back through the circuit to the D,C. input of battery B. This increased power demandcan therefore be detected at any convenient point in the system and used to control the voltage applied to the tube 1. If the voltage on the tube elements, namely the cathode 14, microchannel plate 11 and phosphor screen 22, is caused to decrease as the light-induced tube current increases the tube output light level will remain relatively constant. The variation of tube output brightness A as a function of input illumination is shown in Figure 4.
Figure 3 is a detailed circuit diagram containing some of the components of the block diagram of Figure 2 and describes the operation of the power sensor circuit 37 and the power control circuit 28 in greater detail. D.C. power is ap-plied to the collector of series pass transistor Ql by connection to the positive terminal of battery ~. Current flows through Ql by connection between the emitt0r of Ql and the input to oscillator 27, ~ Osc~llator 27 consists of resistors R2, R3, capacitor Cl, transistor Q3 and transformer Tl connected together to form a class C oscillator. The power control circuit 28 consists of transistors (;~ ' Q2 and resistor Rl. Resistor R2 and capacitor Cl bias ~ransistor Q3 in the active region,and resistor R3 limits mlnimum base current in transistor Q3 and stabilizes the oscillator characteristic for variation in characteristics of transistor Q3. Capacitor C2 connected to the emitter of transistor Ql and the collector of transistor C?3, and to one side of capacitor Cl and resistor R2,provides a low A.C. source impedance to oscillator 27.
Load changes at the secondary S of transformer I'l are reflected back into the pr~mary P and can be sensed by detecting the voltage drop occurring across resistor R4 which is coupled between transformer primary P and ground.
Capacitor C3 coupled between primary P and ground serves to bypass A,C.
components occurring across R4 and should therefore have a reactance that is Alan W. Hoover - 2 low compared to the resistance value R4 at operating frequency of oscillator 27.The emitter of Q3 is connected to one side of transformer prlmary P. One side of R4 is connected to the base of transistor Q2 so that the voltage appearing across R4 is used to control the conduction through transistor Q2 which in turn control the conduction through Ql The collector of Q2 is connected to the base of Ql and the emitter of Q2 is connected to ground. This connection comprises a feedback circuit constructed in such a way as to provide negative feedback such that increasing current through R4 causes the voltage occurring across R4 to increase and the voltage applied to oscillator 27 to decrease. This in turn results in the current through R4 being maintained at a constant value. Thus the effective power sensor 37 could consist of a resistive element connected between the oscillator transformer primary and ground. The combination of the current flow through resistor R4 and the re~sulting voltage drop provide an approx-imate means for determining the effective input power requirements of the image intenslfier. ~ ~
High voltage multipliers 31 and 31' are connected~ to the output of Tl .
Multiplier 31' i9 a 12-stage multiplier which multiplies and rectifies the 500 volt output of Tl to generate +6,000 volts D.C. which is applied directly to thephosphor screen 22, Multiplier 31, oonsisting of a plurality of capacitors and diodes ln voltage doubling arrangement, increases and rectifies the 500 volts provided by transformer Tl to a -1, 000 volts D . C. level for connection to themicrochannel plate 11 and cathode 14. The bPight source protection circuit 10 comprises reslstors R5, R6, R7, R8, connected with diode Dl to form a voltage clamp for maintainlng the voltage applied tp cathode 14 at a predetermined minimum level. Resistors R6 and R7 in parallel with R8 also serve to form a voltage divider in combination with the resistance of the microchannel plate 11.This provides -800 volts across microchannel plate 11 and -200 volts on cathode 14, In order to set the overall intensifier gain level it is necessary to L5~ Alan W. Hoover - 2 ad~ust the voltage level across the microchannel plate ll, This is easily accomplished hy varying the value of resistor R8 rather than adjusting the values of both resistors R6 and R7. The utilization of the circuit components of the bright source protection circuit lO in combination with the reslstance ofmicrochannel plate ll multifunctionally provides the correct voltage for both the tube cathode 14 and microchhanel plate ll without the necessity of a third multiplier as is required with power supplies of the prior art as described earlier. Since both of these tube elements are supplied by the same multiplier 31 and oscillator 27 then the method of sensing efiective input power by means of resistor R,4 and the feedback relationship between transistors Ql and Q2 to control the input power to oscillator 27 is a very slmple method ~or controllingthe light output of tube l, The voltage multiplier provided by the combination of the resistive elements in the BSP circult lO and the resistance of the micro-channel plate ll is possible since the so-called "strip" reslstance of the micro-- 15 channel plate ll is a measured constant value. The strip res~stance for resis-tance to current ~qow provided by the integral electrical properties of the micro-channel plate materlal is typicalls7 in the order of between 106 and 101 ohms, The strip resistance depends to large extent upon the degree of activation of the microchannel plate glass when the glass is of the lead oxide type and is made conductive by treating the glass in a reducing atmosphere~ Resistance values in the order of 108 and lO9 ohms are usually employed, and these values remain relatively constant throughout the liPe of the image tube. Typicalvalues émployed Eor image tube circuits used with image tubes containing microchannel plates are 200 volts betweerl the image tube cathode and the input face of the microchannel plate, and 800 volts between the input and output faces of the microchannel plate. Since the output voltage of the voltage multi-plier 31 is typically in the order of l,000 volts, the resistance values of reslstors R5, A6, R7 and R8 of the BSP clrcuit 10 are chosen so that the voltage _ g _ ;.
s~z Alan W. Hoover - 2 appearln~ between the cathode 14 and the mlcrochannel plate 11 ls approxi-mately 200 volts and the voltage appearlng across microchannel plate 11 is approximately 800 volts when no lnput illumination is caused to fall upon the tube cathode 14.
Prior art power supplies using several oscillators and multipliers to lndividually provide operating power to the tube components generally sense the operating current of one of the tube components, such as the phosphor screen current, and control the tube operating characteristics for this component by varying the microchannel plate voltage. The power requirements of the other tube operating components is not affected. Earlier attempts to control image tube light output by simplified circuit means for monitoring one of the tube operating parameters and providing feedback control to the tube operating voltages have not been successful since the tube parameters such as photocathode current and phosphor screen current represent values in the order of nanoamps. Changes in the order of several nanoamps require complex and expensive circuitry to detect, amplify and use signals of such small value. It was unexpected therefore that changes in the total tube operating power could be useably detecSed in the input power requlrements to the power supply. It was heretofore believed that chanyes in the increasing light level to the tube cathode would have little effect on the tube operating power requirements, nor was it realized that there would be enough change in effective tube power demand with increasing light level to achieve effective control over the tube output light level. Employing constant current control on the primary side of the power supply, however, unexpectedlylprovides high light level tube saturation characteristics which are relatively constant over a five decade range of tube input light illumination Figure 5 shows an alternate arrangement for the controlled power supply of this invention. In the embodiment of Figure 5 the effective power sensing lS~iZ
Alan W. Hoover - 2 reslstor R4 ls connected between the battery B and the emltter of transistor Ql and a zener diode D2 is connected between the base of Ql and the battery B.
Resistor R1 is connected to the base of Q1, the anode of D2 and ground. In this arrangement the diode D2 functions as a reference element, Ql functions as a combined comparison and power control element, and resistor R4 senses the total current change. This clrcuit provides a constant current source independent of input light over a predetermined value of input illumination.
Figure 6 is an alternate embodiment of the circuit of Figure 3 where the effect~ve power sensor resistor R4 is coupled between the output of multi-plier 31 and yround, and capacitor C3 is coupled in parallel with resistor R4.
In this arrangement R4 senses the changes in current in both the cathode 14 and the microcha-nnel plate 11 and reflects these changes in the input circuit to oscillator 27 by connection to the base of transistor Q2 in the manner as described earlier for the power control circuit 37 of the embodiment of Figure 3~.
Although the feedback mechanism is ~described as employing transistors in various arrangements within the power control circuit, it is readily apparent that other circuit elements can be used to provide the feedback and control function. Power sensing elements in the embodiments discussed are resistive type elements which reflect a voltage dlfference in relatlon to the quantity of current transmitted through the element. Other known elements which reflect posltive volt-ampere characteristics, where the voltage increases in relation to current, can also be employed.
The use of the controlled power supply of this invention primarily finds application wlth image tubes that are used for mobile type applications such as night vision devices for military purposes and for providing vision to peoplesuffering from night blind diseases. This is in no way intended as a limitation iZ
Alan W. Hoover - 2 in scope. The controlled power supply oi this lnventLon flnds application wherever compact and lnexpensive clrcuitry is requlred for monitoring light power requirements and for controlling operational power to all type optical-electronic devlces.
RAM: ch December 30, 1975
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A controlled brightness power supply for image tubes of the type containing a micro-channel plate electron multiplier and a phosphor screen comprising: oscillator means for provid-ing A.C. power when coupled with a source of D.C. power; recti-fier means coupled with said oscillator for providing D.C. power to the tube; power sensing means consisting of a resistive element electrically coupled in series between said D.C. power source and said oscillator for detecting changes in tube oper-ating power corresponding to changes in the tube input illumina-tion and reducing the microchannel plate electron multiplier voltage to provide a constant illumination at the phosphor screen; and control circuit means electrically coupled with the power sensor and oscillator in feed-back relation for control-ling the A.C. power in response to the changes in the tube operating power consisting of at least one transistor electri-cally coupled between the oscillator and the D.C. power source to control the conduction through the oscillator.
2. The power supply of claim 1 further including: bright source protection circuit means electrically coupled with the micro-channel plate and the rectifier for preventing increases in tube illumination from damaging the tube cathode said bright source protection circuit consisting of a voltage clamp having resistive means and diode means and wherein the micro-channel plate provides further resistive means to form a vol-tage divider with said voltage clamp.
3. The power supply of claim 1 including: bright source protection circuit means electrically coupled with the micro-channel plate and the rectifier for preventing increases in tube illumination from damaging the tube cathode said bright source protection circuit consisting of a voltage clamp having resistive means and diode means wherein the resistive means comprises a pair of first resistors in series with each other and in common with the cathode of said diode means for setting the operational voltage level of said diode means and a second resistor electrically coupled between one of said first resistors and both the anode of said diode and said tube cathode for sensing the current into said cathode.
4. A controlled brightness power supply for image tubes of the type having a micro-channel plate electron multiplier comprising; oscillator means for providing A.C. power when coupled with a source of D.C. power; rectifier means coupled with said oscillator for providing D.C. power to the tube;
bright source protection circuit means electrically coupled with the micro-channel plate and rectifier for preventing increases in tube illumination from damaging the tube cathode; and at least one resistor serially coupled with at least one output of said micro-channel plate for detecting changes in the tube input illumination and limiting the D.C. power to the oscillator when current through the resistor exceeds a predetermined value.
bright source protection circuit means electrically coupled with the micro-channel plate and rectifier for preventing increases in tube illumination from damaging the tube cathode; and at least one resistor serially coupled with at least one output of said micro-channel plate for detecting changes in the tube input illumination and limiting the D.C. power to the oscillator when current through the resistor exceeds a predetermined value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US646,799 | 1976-01-06 | ||
| US05/646,799 US4037132A (en) | 1976-01-06 | 1976-01-06 | Image tube power supply |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1101562A true CA1101562A (en) | 1981-05-19 |
Family
ID=24594502
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA268,827A Expired CA1101562A (en) | 1976-01-06 | 1976-12-29 | Image tube power supply |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US4037132A (en) |
| CA (1) | CA1101562A (en) |
| DE (1) | DE2700274A1 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4166213A (en) * | 1977-07-08 | 1979-08-28 | International Telephone And Telegraph Corporation | Single power supply multiple image intensifier apparatus and method with independently adjustable low light gain and high light saturation level |
| US5218194A (en) * | 1991-08-19 | 1993-06-08 | Varo Inc. | Advanced high voltage power supply for night vision image intensifer |
| US5729010A (en) * | 1996-09-11 | 1998-03-17 | The United States Of America As Represented By The Secretary Of The Air Force | Night vision device localized irradiance attenuation |
| US5949063A (en) * | 1997-07-28 | 1999-09-07 | Saldana; Michael R. | Night vision device having improved automatic brightness control and bright-source protection, improved power supply for such a night vision device, and method of its operation |
| US5942747A (en) * | 1997-07-28 | 1999-08-24 | Litton Systems, Inc. | Night vision device with voltage to photocathode having a rectified half-sine wave component |
| US5883381A (en) * | 1997-07-28 | 1999-03-16 | Saldana; Michael R. | Night vision device having series regulator in power supply for MCP voltage control |
| US6087649A (en) * | 1997-07-28 | 2000-07-11 | Litton Systems, Inc. | Night vision device having an image intensifier tube, microchannel plate and power supply for such an image intensifier tube, and method |
| US5973315A (en) * | 1998-02-18 | 1999-10-26 | Litton Systems, Inc. | Multi-functional day/night observation, ranging, and sighting device with active optical target acquisition and method of its operation |
| WO1999060787A1 (en) * | 1998-05-18 | 1999-11-25 | Litton Systems, Inc. | Night viewer and laser range finder |
| US6072565A (en) * | 1998-05-18 | 2000-06-06 | Litton Systems, Inc. | Night vision device with improved laser range finder |
| US6278104B1 (en) | 1999-09-30 | 2001-08-21 | Litton Systems, Inc. | Power supply for night viewers |
| JP2001319604A (en) * | 2000-03-30 | 2001-11-16 | Eastman Kodak Co | Circuit for protecting photoelectric cathode of image intensifier |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3665247A (en) * | 1970-07-02 | 1972-05-23 | Machlett Lab Inc | Power regulating means for light amplifier tubes |
| US3848123A (en) * | 1973-03-30 | 1974-11-12 | Rca Corp | Automatic brightness control for image intensifier tube |
| US3864595A (en) * | 1973-04-19 | 1975-02-04 | Westinghouse Electric Corp | Automatic brightness control for gated micro-channel plate intensifier |
-
1976
- 1976-01-06 US US05/646,799 patent/US4037132A/en not_active Expired - Lifetime
- 1976-12-29 CA CA268,827A patent/CA1101562A/en not_active Expired
-
1977
- 1977-01-05 DE DE19772700274 patent/DE2700274A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| US4037132A (en) | 1977-07-19 |
| DE2700274A1 (en) | 1977-07-14 |
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