Variable voltage divider
United States Patent 3909769
A variable voltage divider having a ceramic substrate supporting a plurality of resistive paths and comprising an arcuate resistive path disposed between two fixed resistive paths, the fixed resistive paths being abraded to achieve a proper resistance ratio between each of the two fixed resistor paths and the arcuate resistive path, a plurality of terminations, a center collector, and a driver mounted in a center aperture in the substrate and carrying a contactor, the contactor wipingly engaging the collector and the arcuate resistive path. The ceramic substrate is enclosed in a housing and contains registration means for locating the substrate in the housing, the two fixed resistive paths being arcuately disposed about said registration means.
US Patent References:
High voltage controls
Arisman et al. - April 1957 - 2789191
Rheostat with fixed resistors
Littleton - October 1958 - 2858397
Multiple variable resistance control with common snap-in mounting
Budd - January 1959 - 2871324
Resistance trimmer
Kilby et al. - April 1959 - 2883499
MOUNTING BRACKET FOR ELECTRICAL COMPONENT
Beuthuyseu et al. - January 1969 - 3421133
High voltage controls
Arisman et al. - April 1957 - 2789191
Rheostat with fixed resistors
Littleton - October 1958 - 2858397
Multiple variable resistance control with common snap-in mounting
Budd - January 1959 - 2871324
Resistance trimmer
Kilby et al. - April 1959 - 2883499
MOUNTING BRACKET FOR ELECTRICAL COMPONENT
Beuthuyseu et al. - January 1969 - 3421133
Inventors:
Rozema, Arthur L. (Elkhart, IN)
Alm, Howard G. (Fairbury, IL)
Alm, Howard G. (Fairbury, IL)
Application Number:
05/411400
Publication Date:
09/30/1975
Filing Date:
10/31/1973
View Patent Images:
Export Citation:
Assignee:
CTS Corporation (Elkhart, IN)
Primary Class:
Other Classes:
338/164, 338/199, 338/184, 338/163
International Classes:
H01C10/34; H01C10/00; H01C10/34
Field of Search:
338/48,128,68,118,162,163,164,174,184,199
US Patent References:
Primary Examiner:
Reynolds, Bruce A.
Claims:
What is claimed as new and desired to be secured by Letters Patent of the United States is
1. A variable voltage divider comprising a dielectric substrate, a plurality of conductive terminations, including one relatively high voltage termination, supported on said substrate, resistance means comprising first, second and third resistive paths supported on said substrate, one end of said second resistive path being connected to said first resistive path and the other end of said second resistive path being connected to said high voltage termination, one end of the third resistive path being connected to a second one of the terminations and the other end of the third resistive path being connected to said first resistive path, a collector supported on said substrate, adjusting means supported for movement relative to said substrate, and a conductive contactor constrained to move with said adjusting means and wipably engaging the first resistive path and the collector, said substrate comprising registration means for locating the substrate in a housing, said registration means comprising a first registration means and a second registration means spaced apart from said first registration means, said second resistive path being arcuately disposed about one of said registration means and said third resistive path being arcuately disposed about the other of said registration means.
2. The voltage divider of claim 1, wherein said first resistive path is circularly disposed about an aperture provided in said substrate and said adjusting means contains a contactor driver supported in said aperture and overlying said first resistive path, said contactor driver overlying a significant portion of the area of said substrate, said second and third resistive paths being disposed on the remaining area of said substrate.
3. The voltage divider of claim 2, comprising a housing containing locator means and provided with an opening and a receptacle communicating with said opening, wherein said substrate contains registration means engageable with said locator means to locate the substrate in the housing, and wherein said adjusting means contains a contactor driver disposed in said receptacle, said driver containing a first surface and a second surface spaced apart from said first surface and substantially parallel thereto, said first surface containing an integral knob portion extending through said opening and said second surface containing an integral shaft portion secured in said aperture.
4. The voltage divider of claim 1, comprising a housing and locator pins secured to said housing, wherein said first registration means is a first hole at one end of the substrate and said second registration means is a second hole at the other end of said substrate, one of said locator pins extending through each of said holes.
5. The voltage divider of claim 4, wherein said housing is provided with an opening and said substrate is provided with an aperture, said locator pins being disposed in a line with said opening and said locator holes being disposed in a line with said aperture, portions of said locator pins being swaged to the substrate and securing the substrate to the housing, a portion of said adjustment means extending through said opening.
6. The voltage divider of claim 5, wherein said housing comprises an integral bushing and is provided with an annular bearing, said bearing and said bushing being concentrically disposed about said opening.
7. A variable voltage divider comprising a housing containing locator means and a receptacle, a dielectric substrate containing registration means engaging said locator means and locating substrate in the housing, a center aperture, a plurality of conductive terminations supported on said substrate, resistance means comprising a first, a second, and a third resistive path supported on said substrate, one end of said second resistive path being connected to one end of said first resistive path, one end of said third resistive path being connected to the other end of said first resistive path, the other end of said second resistive path being connected to a first one of the conductive terminations, and the other end of said third resistive path being connected to a second one of the conductive terminations, a collector supported on said substrate, and adjusting means extending into said center aperture and supported for movement relative to said substrate, said adjusting means containing a contactor driver overlying said first resistive path, said driver disposed in the receptacle of said housing, and a conductive contactor constrained to move with said contactor driver and wipingly engaging the first resistive path and the collector, said first resistive path being circularly disposed about said center aperture in the substrate, said registration means comprising a first registration means and a second registration means spaced apart from said first registration means, said second resistive path being arcuately disposed about one of said registration means and said third resistive path being arcuately disposed about the other of said registration means.
8. The voltage divider of claim 7 wherein said contactor driver contains a first surface, said first surface containing an integral shaft portion secured in the center aperture of said substrate, said driver overlying approximately one-half of the area of the substrate, said second and third resistive paths being disposed on the remaining area of said substrate.
9. A variable voltage divider for use in circuits having a DC voltage in the range of 6,000 volts and higher, the divider comprising a substantially rectangular dielectric substrate containing an aperture centrally located as to one of the width or the length of the substrate, the substrate being provided with a pair of locating holes on opposite end of the substrate, for locating the substrate in a housing, the centers of the aperture and the locating holes lying substantially in a straight line, a plurality of conductive terminations supported on the substrate, an arcuate resistor and first and second fixed resistors secured on a surface on one side of the substrate, one end of the first fixed resistor being electrically connected to one end of the arcuate resistor and the other end of the first fixed resistor being electrically connected to a first one of the terminations, the other end of the arcuate resistor being electrically connected to one end of the second fixed resistor and the other end of the second fixed resistor being electrically connected to a second one of the terminations, the arcuate resistor being disposed between the first and second fixed resistors, the first fixed resistor and the second fixed resistor defining a designated resistance ratio, the resistance ratio between the first fixed resistor and the second fixed resistor being dependent upon the resistance of the arcuate resistor, a collector supported on the substrate and circumposing at least a portion of the aperture and electrically connected to a third one of the terminations, a driver, a shaft connected to the driver and extending into the aperture and rotatably supporting the driver for movement relative to the substrate, the diameter of the driver being substantially equal to the maximum width of the substrate, a contactor constrained for movement with the driver and wipably engaging the arcuate resistor and the collector for altering the voltage between the first one and the third one of the terminations.
10. The voltage divider of claim 9, wherein a third fixed resistor is disposed between the collector and the third one of the terminations.
1. A variable voltage divider comprising a dielectric substrate, a plurality of conductive terminations, including one relatively high voltage termination, supported on said substrate, resistance means comprising first, second and third resistive paths supported on said substrate, one end of said second resistive path being connected to said first resistive path and the other end of said second resistive path being connected to said high voltage termination, one end of the third resistive path being connected to a second one of the terminations and the other end of the third resistive path being connected to said first resistive path, a collector supported on said substrate, adjusting means supported for movement relative to said substrate, and a conductive contactor constrained to move with said adjusting means and wipably engaging the first resistive path and the collector, said substrate comprising registration means for locating the substrate in a housing, said registration means comprising a first registration means and a second registration means spaced apart from said first registration means, said second resistive path being arcuately disposed about one of said registration means and said third resistive path being arcuately disposed about the other of said registration means.
2. The voltage divider of claim 1, wherein said first resistive path is circularly disposed about an aperture provided in said substrate and said adjusting means contains a contactor driver supported in said aperture and overlying said first resistive path, said contactor driver overlying a significant portion of the area of said substrate, said second and third resistive paths being disposed on the remaining area of said substrate.
3. The voltage divider of claim 2, comprising a housing containing locator means and provided with an opening and a receptacle communicating with said opening, wherein said substrate contains registration means engageable with said locator means to locate the substrate in the housing, and wherein said adjusting means contains a contactor driver disposed in said receptacle, said driver containing a first surface and a second surface spaced apart from said first surface and substantially parallel thereto, said first surface containing an integral knob portion extending through said opening and said second surface containing an integral shaft portion secured in said aperture.
4. The voltage divider of claim 1, comprising a housing and locator pins secured to said housing, wherein said first registration means is a first hole at one end of the substrate and said second registration means is a second hole at the other end of said substrate, one of said locator pins extending through each of said holes.
5. The voltage divider of claim 4, wherein said housing is provided with an opening and said substrate is provided with an aperture, said locator pins being disposed in a line with said opening and said locator holes being disposed in a line with said aperture, portions of said locator pins being swaged to the substrate and securing the substrate to the housing, a portion of said adjustment means extending through said opening.
6. The voltage divider of claim 5, wherein said housing comprises an integral bushing and is provided with an annular bearing, said bearing and said bushing being concentrically disposed about said opening.
7. A variable voltage divider comprising a housing containing locator means and a receptacle, a dielectric substrate containing registration means engaging said locator means and locating substrate in the housing, a center aperture, a plurality of conductive terminations supported on said substrate, resistance means comprising a first, a second, and a third resistive path supported on said substrate, one end of said second resistive path being connected to one end of said first resistive path, one end of said third resistive path being connected to the other end of said first resistive path, the other end of said second resistive path being connected to a first one of the conductive terminations, and the other end of said third resistive path being connected to a second one of the conductive terminations, a collector supported on said substrate, and adjusting means extending into said center aperture and supported for movement relative to said substrate, said adjusting means containing a contactor driver overlying said first resistive path, said driver disposed in the receptacle of said housing, and a conductive contactor constrained to move with said contactor driver and wipingly engaging the first resistive path and the collector, said first resistive path being circularly disposed about said center aperture in the substrate, said registration means comprising a first registration means and a second registration means spaced apart from said first registration means, said second resistive path being arcuately disposed about one of said registration means and said third resistive path being arcuately disposed about the other of said registration means.
8. The voltage divider of claim 7 wherein said contactor driver contains a first surface, said first surface containing an integral shaft portion secured in the center aperture of said substrate, said driver overlying approximately one-half of the area of the substrate, said second and third resistive paths being disposed on the remaining area of said substrate.
9. A variable voltage divider for use in circuits having a DC voltage in the range of 6,000 volts and higher, the divider comprising a substantially rectangular dielectric substrate containing an aperture centrally located as to one of the width or the length of the substrate, the substrate being provided with a pair of locating holes on opposite end of the substrate, for locating the substrate in a housing, the centers of the aperture and the locating holes lying substantially in a straight line, a plurality of conductive terminations supported on the substrate, an arcuate resistor and first and second fixed resistors secured on a surface on one side of the substrate, one end of the first fixed resistor being electrically connected to one end of the arcuate resistor and the other end of the first fixed resistor being electrically connected to a first one of the terminations, the other end of the arcuate resistor being electrically connected to one end of the second fixed resistor and the other end of the second fixed resistor being electrically connected to a second one of the terminations, the arcuate resistor being disposed between the first and second fixed resistors, the first fixed resistor and the second fixed resistor defining a designated resistance ratio, the resistance ratio between the first fixed resistor and the second fixed resistor being dependent upon the resistance of the arcuate resistor, a collector supported on the substrate and circumposing at least a portion of the aperture and electrically connected to a third one of the terminations, a driver, a shaft connected to the driver and extending into the aperture and rotatably supporting the driver for movement relative to the substrate, the diameter of the driver being substantially equal to the maximum width of the substrate, a contactor constrained for movement with the driver and wipably engaging the arcuate resistor and the collector for altering the voltage between the first one and the third one of the terminations.
10. The voltage divider of claim 9, wherein a third fixed resistor is disposed between the collector and the third one of the terminations.
Description:
The invention relates generally to voltage divider controls and more particularly to controls that are particularly suitable for use as variable voltage dividers.
Variable voltage dividers such as disclosed in U.S. Pat. No. 3,585,559, assigned to the same assignee as the present invention, generally comprise a substrate containing three resistive paths, a collector, a contactor wipingly engaging one of the resistive paths and the collector, a driver for changing the position of the contactor relative to the resistive paths, and a plurality of termination means for connecting the voltage divider with the circuitry of suitable electronic apparatus. The termination means include a high voltage input termination, a low voltage or ground termination and an output termination. The resistive paths include an arcuate resistive path, a fixed resistive path connected to the arcuate resistive path and a current limiting resistive path interconnecting the collector and the output termination.
More sophisticated electronic equipment requires that the voltage dividers be more compact physically and geometrically as well as be able to handle much higher voltages. Specifically, in one application, variable voltage dividers are used to supply a constant voltage to the focus electrode of cathode ray tubes. In this application, the input end of the voltage divider is connected to a relatively high potential power supply, the ground end of the divider is connected to a low potential or ground, and the output termination of the divider is connected to the focus electrode of the tube. In typical television picture tube applications, the input to the voltage divider has been connected to a DC voltage of approximately 6,000 volts. However, because of advances in picture tube technology, a DC voltage in the range of 8,300 - 10,500 volts is now connected to the input of the voltage divider. This has necessitated the use of additional electrical resistance in the form of an additional resistive path, in the voltage divider circuit to achieve a suitable voltage at the output termination. In addition, some applications require that the additional circuitry required to control the higher voltages be compressed onto a smaller substrate than heretofore required. It would therefore be desirable to provide a variable voltage divider capable of controlling increased power supply voltages and yet smaller and more compact than prior art voltage dividers.
Another problem with prior art controls such as disclosed in the above mentioned patent, was the exposure of the control to the environment. Thus metal objects or particles could come into contact with the voltage divider and short out the control. In addition, due to the high voltages carried by the voltage divider, a serious safety hazard existed during the maintenance and servicing of the electronic equipment containing the voltage divider. It would therefore be desirable to provide a variable voltage divider that minimizes potential shorting out of the control as well as providing a divider that eliminates the safety hazard that exists during the servicing of the electronic equipment containing the voltage divider.
Another problem in prior art variable voltage dividers was that the resistance values of each of the resistive paths had to be held to acceptable tolerances in order to obtain the required output voltages. This can be very difficult due to the many factors that can affect the resistance value of a resistance path such as changes in the formulation of the resistive material, changes in atmospheric conditions during the screening or application of the resistive material to the substrate, changes in the firing cycle of the resistive material, and changes in the configuration of the resistive path such as path thickness. As a result, the inability of even one of the various resistive paths to meet the tolerances often resulted in rejection of the entire voltage divider. In the present invention, even with the addition of an additional resistive path creating even more potential for the divider to be out of tolerance, it has been found that the production yields are significantly increased by the inclusion of a relatively simple step in the assembly of the variable voltage divider. That step consists of the abrading of particular resistive paths after the resistive paths have been screened on the substrate and fired.
The present invention comprises an arcuate resistive path connected between two fixed resistive paths with one of the fixed resistive paths connected to the input voltage, the other fixed resistive path connected to a low voltage or ground, and the output voltage taken from the arcuate resistive path. Rather than attempting to apply the resistive paths with relatively close tolerances, however, the two fixed resistive paths are applied to the substrate at a resistance value substantially lower than normally required. To achieve a desired output voltage for a given input voltage, it is only necessary that the ratio of the resistance of each of the fixed resistive paths to the resistance of the arcuate resistive path be at a predetermined value. Regardless of the absolute value of each of the resistive paths, if the ratios equal the predetermined value, the output voltage will be in the proper range. Therefore, after the resistive paths have been screened on the substrate and fired, portions of each of the fixed resistive paths are abraded to increase the resistance and to obtain the predetermined ratio. This procedure establishes the desired range of output voltage values as well as permits a much wider range of tolerance in the screening of the resistive paths. This has resulted in a substantial increase in production yield. It would therefore be desirable to produce a variable voltage divider that could obtain a desired output voltage range without the necessity of holding the various resistive paths to close tolerances and it would be desirable to produce a voltage divider that obtains high production yields.
Accordingly, it is an object of the present invention to provide a new and improved voltage divider which is small and compact in size and has increased voltage handling capability. Another object of the present invention is to provide an improved variable voltage divider containing an arcuate resistive path and two fixed resistive paths in alignment on opposite sides of the arcuate resistive path and wherein the fixed resistive paths are abraded to achieve a predetermined ratio of the resistance of each fixed resistive path to the resistance of the arcuate resistive path. A further object of the present invention is to provide a new and improved voltage divider containing a housing with a center aperture and locator pins, a substrate with registration means for locating the substrate in the housing and actuating means secured to said substrate and having a knob portion extending through the center aperture of the housing. A further object of the invention is to provide a substrate containing a center aperture and registration means and wherein the arcuate resistive path is disposed about the center aperture and the fixed resistive paths are disposed about said registration means. Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.
Briefly, the present invention is concerned with a variable voltage divider having a ceramic substrate supporting a plurality of resistive paths on a surface thereof, the resistive paths comprising an arcuate resistive path connecting two fixed resistive paths, a contactor driver overlying said surface and having a shaft portion projecting through said center aperture, a conductive contactor wipingly engaging one of the resistive paths and the center collector and constrained to rotate with the contactor driver, and a termination disposed at one end of the fixed resistive paths including a termination disposed at one end of a fixed resistive path connected to the center collector. The substrate further contains a center aperture and registration means for locating the substrate in a housing, the arcuate resistive path being disposed about the center aperture and the two fixed resistive paths connected to the arcuate resistive path being arcuately disposed about said registration means. In addition, the fixed resistive paths connected to the arcuate resistive path are abraded to achieve a predetermined ratio between the resistance value of each of the fixed resistive paths and the resistance value of the arcuate resistive path.
For a better understanding of the present invention reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein:
FIG. 1 is an isometric view of a variable voltage divider built in accord with the present invention;
FIG. 2 is a sectional view taken along the line II--II of FIG. 1;
FIG. 3 is an exploded isometric view of the variable voltage divider of FIG. 1; and
FIG. 4 is a plan view of the contactor driver assembled to the substrate in accord with the present invention.
Referring now to FIGS. 1 through 4, there is illustrated a variable voltage divider generally indicated by the numberal 10 comprising a housing 40 formed of thermo-plastic or other suitable dielectric material, a substrate 12 formed of a dielectric material such as alumina or glass and containing a first surface 13a and a second surface 13b spaced apart from and parallel to surface 13a, the surface 13a supporting resistance means in the form of a first resistive path 14, a second resistive path 16, a third resistive path 18 and a fourth resistive path 20, and supporting a conductive collector 22 and a plurality of conductive pads or terminations 27, 28 and 29 with a plurality of terminals 30 connected thereto. The substrate 12 further contains a center aperture 32, a pair of locator holes or registration means 34, and terminal holes 36, each of the terminal holes being associated with one of the conductive pads and a terminal 30, and the housing 40 contains a center aperture 42 and a surface 44 containing a pair of locator pins 46, the locator pins 46 extending through the locator holes 34 to locate the substrate 12 within the housing 40, the locator pins 46 being heat swaged against the surface 13b of substrate 12 to secure the substrate within the housing.
The conductive pads or terminations 27, 28 and 29 are preferably comprised of a film of palladium gold or other suitable solderable conductive material that would form a good electrical connection with the material used to make the resistive paths. The same material may also be used for the collector 22 and may be applied in any suitable manner, e.g., by screening. By making the resistive paths 14, 16, 18, 20 from a common cermet formulation and by applying these paths to a common surface 13a of the substrate 12, variations occurring in the processing of the resistive paths such as variations in the pressures used while applying the resistive paths to the surface of the substrate or variations in firing time or temperature will have substantially an identical effect on each of the resistive paths. Hereinafter the conductive pad 27 will be referred to as the input termination, the conductive pad 28 will be referred to as the low potential or grounded termination, and the conductive pad 29 will be referred to as the output termination.
The housing further contains a surface 50 containing grooves 52, the surface 44 containing a recess 48 joining each of the grooves 52 at the intersection of surface 44 with surface 50. As best seen in FIGURE 2 the recesses 48 and grooves 52 allow the terminals 30 to extend through terminal holes 36 and wrap around a portion 39 of the substrate 12 without impeding a secure fit of the substrate 12 within the housing 40. Each of the terminals 30 contains a back portion 70 located in a recess 48, a bottom portion 72 located in a groove 52 and a clip portion 74 causing the terminal 30 to wrap around a portion 39 of substrate 12, a solder deposit 76 electrically connecting the terminals 30 to the conductive pads. The housing 40 also contains a mounting pin 64, as seen in FIG. 1, for locating the housing on a not shown panel, the knurled adjusting shaft 31 extending through a hole in the panel and engaging a fitting to secure the housing to the panel, or alternately, the housing 40 may contain not shown mounting ears extending from the housing to snap the housing in place on a mounting panel.
A preferred form of adjusting means for repeatedly changing the setting of the voltage divider 10 comprises a conductive contactor 21 trapped and resiliently compressed between the planor surfaces 13a of the substrate 12 and 37 of the contactor driver 23, the contactor being constrained to rotate with the driver because of the interengagement of the pair of ears 24a and 24b on the contactor with a pair of notches 25 formed in surface 37 of the contactor driver. In order to secure assembly of the contactor driver 23 and the conductive contactor 21 with the substrate 12, an alignment member illustrated as a stub shaft 26 is formed integrally with the contactor driver and aligns the contactor driver with the substrate by projecting through the center aperture 32 in the substrate 12. As best illustrated in FIG. 2, an end 26a of the stub shaft 26 is enlarged by heat swaging and forms a bearing 26b against a surface 13b of the substrate. The contactor driver 22 also includes the knurled adjusting shaft 31 that facilitates manual adjustement of the divider, the shaft 31 extending through aperture 42 in the housing 40. In order to space the driver 23 from the surface 13a of the substrate and to provide for smooth adjustment of the control, a bearing 33 is provided on the surface 37 of the driver 23.
Rotational movement of the driver is limited by the stop arm 35 projecting from surface 38 of the driver 23, the surface 38 spaced apart from the parallel to surface 37. As seen in FIG. 3, the housing 40 contains a circular receptacle 49 for receiving the contactor driver 23, the receptacle 49 defined by annular wall 51. A surface 56 defines the bottom of receptacle 49 and receptacle 49 contains another surface 54 elevated with respect to surface 56, the surfaces 54 and 56 defining a passageway 58. When the driver is assembled in the housing, the surface 38 of the driver abuts the surface 54 of the housing, the stop arm 35 being disposed in passageway 58. Abutment surfaces 60 and 61 form the ends of passageway 58 and engage stop arm 35 as the stop arm is rotated by the driver 23 to the limits of passageway 58, thus halting the rotational movement of the driver 23.
The variable voltage divider is formed by first applying the resistive paths on the substrate, firing the substrate, then applying the conductive pads and firing the substrate again. Fixed resistive paths 14 and 18 are then abraded so that the ratio of the resistance of each of the paths 14 and 18 to the resistance of the arcuate resistive path 16 is a predetermined value. As seen in FIG. 4, the resistive path 16 is disposed intermediate the fixed resistive paths 14 and 18, the resistive path 16 being circularly disposed about the center aperture 32 and each of the fixed resistive paths 14 and 18 being disposed about one of the locator holes 34 respectively. One end of the resistive path 18 is connected to the input termination 27 and one end of the resistive path 14 is connected to the ground termination 28, the output termination 29 being connected to fixed resistive path 20. For a given voltage input as long as the resistance ratios of the paths 14 and 18 to the path 16 equal predetermined values, the output voltage range over the limits of the arcuate resistive path 16 will be constant regardless of the absolute value of the resistive paths 14, 16 and 18. Therefore, the resistive paths 14 and 18 are applied to the substrate at a value generally lower than required.
After the resistive paths and conductive pads have been applied to the substrate and fired, each of the resistive paths 14 and 18 is abraded. The removal of portions of resistive paths 14 and 18 can be by laser abrading or any other suitable abrading procedure. This step can be automated with, for example, a laser abrader automatically removing portions of the resistive paths 14 and 18 until the ratio of each of the paths 14 and 18 to the path 16 reached a predetermined level, automatically stopping the abrading operation. Each of the fixed resistive paths 14 and 18 contains a wide portion 17 and a narrow portion 19, the wide portion abraded at 77 to increase the resistance of that particular resistive path.
Compactness of the voltage divider is achieved by the symmetric placement of each of the resistive paths 14 and 18 on either side of the arcuate resistive path 16, each of the fixed resistive paths disposed around the locator holes 34. As best seen in FIG. 4, the driver 23 and the resistive paths 14 and 18 are compactly placed on substrate 12, the driver 23 overlying approximately one-half the area of the substrate, the resistive paths 14 and 18 disposed on the remaining area of the substrate.
While there has been illustrated and described what is at present considered to be a preferred embodiment of the present invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.
Variable voltage dividers such as disclosed in U.S. Pat. No. 3,585,559, assigned to the same assignee as the present invention, generally comprise a substrate containing three resistive paths, a collector, a contactor wipingly engaging one of the resistive paths and the collector, a driver for changing the position of the contactor relative to the resistive paths, and a plurality of termination means for connecting the voltage divider with the circuitry of suitable electronic apparatus. The termination means include a high voltage input termination, a low voltage or ground termination and an output termination. The resistive paths include an arcuate resistive path, a fixed resistive path connected to the arcuate resistive path and a current limiting resistive path interconnecting the collector and the output termination.
More sophisticated electronic equipment requires that the voltage dividers be more compact physically and geometrically as well as be able to handle much higher voltages. Specifically, in one application, variable voltage dividers are used to supply a constant voltage to the focus electrode of cathode ray tubes. In this application, the input end of the voltage divider is connected to a relatively high potential power supply, the ground end of the divider is connected to a low potential or ground, and the output termination of the divider is connected to the focus electrode of the tube. In typical television picture tube applications, the input to the voltage divider has been connected to a DC voltage of approximately 6,000 volts. However, because of advances in picture tube technology, a DC voltage in the range of 8,300 - 10,500 volts is now connected to the input of the voltage divider. This has necessitated the use of additional electrical resistance in the form of an additional resistive path, in the voltage divider circuit to achieve a suitable voltage at the output termination. In addition, some applications require that the additional circuitry required to control the higher voltages be compressed onto a smaller substrate than heretofore required. It would therefore be desirable to provide a variable voltage divider capable of controlling increased power supply voltages and yet smaller and more compact than prior art voltage dividers.
Another problem with prior art controls such as disclosed in the above mentioned patent, was the exposure of the control to the environment. Thus metal objects or particles could come into contact with the voltage divider and short out the control. In addition, due to the high voltages carried by the voltage divider, a serious safety hazard existed during the maintenance and servicing of the electronic equipment containing the voltage divider. It would therefore be desirable to provide a variable voltage divider that minimizes potential shorting out of the control as well as providing a divider that eliminates the safety hazard that exists during the servicing of the electronic equipment containing the voltage divider.
Another problem in prior art variable voltage dividers was that the resistance values of each of the resistive paths had to be held to acceptable tolerances in order to obtain the required output voltages. This can be very difficult due to the many factors that can affect the resistance value of a resistance path such as changes in the formulation of the resistive material, changes in atmospheric conditions during the screening or application of the resistive material to the substrate, changes in the firing cycle of the resistive material, and changes in the configuration of the resistive path such as path thickness. As a result, the inability of even one of the various resistive paths to meet the tolerances often resulted in rejection of the entire voltage divider. In the present invention, even with the addition of an additional resistive path creating even more potential for the divider to be out of tolerance, it has been found that the production yields are significantly increased by the inclusion of a relatively simple step in the assembly of the variable voltage divider. That step consists of the abrading of particular resistive paths after the resistive paths have been screened on the substrate and fired.
The present invention comprises an arcuate resistive path connected between two fixed resistive paths with one of the fixed resistive paths connected to the input voltage, the other fixed resistive path connected to a low voltage or ground, and the output voltage taken from the arcuate resistive path. Rather than attempting to apply the resistive paths with relatively close tolerances, however, the two fixed resistive paths are applied to the substrate at a resistance value substantially lower than normally required. To achieve a desired output voltage for a given input voltage, it is only necessary that the ratio of the resistance of each of the fixed resistive paths to the resistance of the arcuate resistive path be at a predetermined value. Regardless of the absolute value of each of the resistive paths, if the ratios equal the predetermined value, the output voltage will be in the proper range. Therefore, after the resistive paths have been screened on the substrate and fired, portions of each of the fixed resistive paths are abraded to increase the resistance and to obtain the predetermined ratio. This procedure establishes the desired range of output voltage values as well as permits a much wider range of tolerance in the screening of the resistive paths. This has resulted in a substantial increase in production yield. It would therefore be desirable to produce a variable voltage divider that could obtain a desired output voltage range without the necessity of holding the various resistive paths to close tolerances and it would be desirable to produce a voltage divider that obtains high production yields.
Accordingly, it is an object of the present invention to provide a new and improved voltage divider which is small and compact in size and has increased voltage handling capability. Another object of the present invention is to provide an improved variable voltage divider containing an arcuate resistive path and two fixed resistive paths in alignment on opposite sides of the arcuate resistive path and wherein the fixed resistive paths are abraded to achieve a predetermined ratio of the resistance of each fixed resistive path to the resistance of the arcuate resistive path. A further object of the present invention is to provide a new and improved voltage divider containing a housing with a center aperture and locator pins, a substrate with registration means for locating the substrate in the housing and actuating means secured to said substrate and having a knob portion extending through the center aperture of the housing. A further object of the invention is to provide a substrate containing a center aperture and registration means and wherein the arcuate resistive path is disposed about the center aperture and the fixed resistive paths are disposed about said registration means. Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.
Briefly, the present invention is concerned with a variable voltage divider having a ceramic substrate supporting a plurality of resistive paths on a surface thereof, the resistive paths comprising an arcuate resistive path connecting two fixed resistive paths, a contactor driver overlying said surface and having a shaft portion projecting through said center aperture, a conductive contactor wipingly engaging one of the resistive paths and the center collector and constrained to rotate with the contactor driver, and a termination disposed at one end of the fixed resistive paths including a termination disposed at one end of a fixed resistive path connected to the center collector. The substrate further contains a center aperture and registration means for locating the substrate in a housing, the arcuate resistive path being disposed about the center aperture and the two fixed resistive paths connected to the arcuate resistive path being arcuately disposed about said registration means. In addition, the fixed resistive paths connected to the arcuate resistive path are abraded to achieve a predetermined ratio between the resistance value of each of the fixed resistive paths and the resistance value of the arcuate resistive path.
For a better understanding of the present invention reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein:
FIG. 1 is an isometric view of a variable voltage divider built in accord with the present invention;
FIG. 2 is a sectional view taken along the line II--II of FIG. 1;
FIG. 3 is an exploded isometric view of the variable voltage divider of FIG. 1; and
FIG. 4 is a plan view of the contactor driver assembled to the substrate in accord with the present invention.
Referring now to FIGS. 1 through 4, there is illustrated a variable voltage divider generally indicated by the numberal 10 comprising a housing 40 formed of thermo-plastic or other suitable dielectric material, a substrate 12 formed of a dielectric material such as alumina or glass and containing a first surface 13a and a second surface 13b spaced apart from and parallel to surface 13a, the surface 13a supporting resistance means in the form of a first resistive path 14, a second resistive path 16, a third resistive path 18 and a fourth resistive path 20, and supporting a conductive collector 22 and a plurality of conductive pads or terminations 27, 28 and 29 with a plurality of terminals 30 connected thereto. The substrate 12 further contains a center aperture 32, a pair of locator holes or registration means 34, and terminal holes 36, each of the terminal holes being associated with one of the conductive pads and a terminal 30, and the housing 40 contains a center aperture 42 and a surface 44 containing a pair of locator pins 46, the locator pins 46 extending through the locator holes 34 to locate the substrate 12 within the housing 40, the locator pins 46 being heat swaged against the surface 13b of substrate 12 to secure the substrate within the housing.
The conductive pads or terminations 27, 28 and 29 are preferably comprised of a film of palladium gold or other suitable solderable conductive material that would form a good electrical connection with the material used to make the resistive paths. The same material may also be used for the collector 22 and may be applied in any suitable manner, e.g., by screening. By making the resistive paths 14, 16, 18, 20 from a common cermet formulation and by applying these paths to a common surface 13a of the substrate 12, variations occurring in the processing of the resistive paths such as variations in the pressures used while applying the resistive paths to the surface of the substrate or variations in firing time or temperature will have substantially an identical effect on each of the resistive paths. Hereinafter the conductive pad 27 will be referred to as the input termination, the conductive pad 28 will be referred to as the low potential or grounded termination, and the conductive pad 29 will be referred to as the output termination.
The housing further contains a surface 50 containing grooves 52, the surface 44 containing a recess 48 joining each of the grooves 52 at the intersection of surface 44 with surface 50. As best seen in FIGURE 2 the recesses 48 and grooves 52 allow the terminals 30 to extend through terminal holes 36 and wrap around a portion 39 of the substrate 12 without impeding a secure fit of the substrate 12 within the housing 40. Each of the terminals 30 contains a back portion 70 located in a recess 48, a bottom portion 72 located in a groove 52 and a clip portion 74 causing the terminal 30 to wrap around a portion 39 of substrate 12, a solder deposit 76 electrically connecting the terminals 30 to the conductive pads. The housing 40 also contains a mounting pin 64, as seen in FIG. 1, for locating the housing on a not shown panel, the knurled adjusting shaft 31 extending through a hole in the panel and engaging a fitting to secure the housing to the panel, or alternately, the housing 40 may contain not shown mounting ears extending from the housing to snap the housing in place on a mounting panel.
A preferred form of adjusting means for repeatedly changing the setting of the voltage divider 10 comprises a conductive contactor 21 trapped and resiliently compressed between the planor surfaces 13a of the substrate 12 and 37 of the contactor driver 23, the contactor being constrained to rotate with the driver because of the interengagement of the pair of ears 24a and 24b on the contactor with a pair of notches 25 formed in surface 37 of the contactor driver. In order to secure assembly of the contactor driver 23 and the conductive contactor 21 with the substrate 12, an alignment member illustrated as a stub shaft 26 is formed integrally with the contactor driver and aligns the contactor driver with the substrate by projecting through the center aperture 32 in the substrate 12. As best illustrated in FIG. 2, an end 26a of the stub shaft 26 is enlarged by heat swaging and forms a bearing 26b against a surface 13b of the substrate. The contactor driver 22 also includes the knurled adjusting shaft 31 that facilitates manual adjustement of the divider, the shaft 31 extending through aperture 42 in the housing 40. In order to space the driver 23 from the surface 13a of the substrate and to provide for smooth adjustment of the control, a bearing 33 is provided on the surface 37 of the driver 23.
Rotational movement of the driver is limited by the stop arm 35 projecting from surface 38 of the driver 23, the surface 38 spaced apart from the parallel to surface 37. As seen in FIG. 3, the housing 40 contains a circular receptacle 49 for receiving the contactor driver 23, the receptacle 49 defined by annular wall 51. A surface 56 defines the bottom of receptacle 49 and receptacle 49 contains another surface 54 elevated with respect to surface 56, the surfaces 54 and 56 defining a passageway 58. When the driver is assembled in the housing, the surface 38 of the driver abuts the surface 54 of the housing, the stop arm 35 being disposed in passageway 58. Abutment surfaces 60 and 61 form the ends of passageway 58 and engage stop arm 35 as the stop arm is rotated by the driver 23 to the limits of passageway 58, thus halting the rotational movement of the driver 23.
The variable voltage divider is formed by first applying the resistive paths on the substrate, firing the substrate, then applying the conductive pads and firing the substrate again. Fixed resistive paths 14 and 18 are then abraded so that the ratio of the resistance of each of the paths 14 and 18 to the resistance of the arcuate resistive path 16 is a predetermined value. As seen in FIG. 4, the resistive path 16 is disposed intermediate the fixed resistive paths 14 and 18, the resistive path 16 being circularly disposed about the center aperture 32 and each of the fixed resistive paths 14 and 18 being disposed about one of the locator holes 34 respectively. One end of the resistive path 18 is connected to the input termination 27 and one end of the resistive path 14 is connected to the ground termination 28, the output termination 29 being connected to fixed resistive path 20. For a given voltage input as long as the resistance ratios of the paths 14 and 18 to the path 16 equal predetermined values, the output voltage range over the limits of the arcuate resistive path 16 will be constant regardless of the absolute value of the resistive paths 14, 16 and 18. Therefore, the resistive paths 14 and 18 are applied to the substrate at a value generally lower than required.
After the resistive paths and conductive pads have been applied to the substrate and fired, each of the resistive paths 14 and 18 is abraded. The removal of portions of resistive paths 14 and 18 can be by laser abrading or any other suitable abrading procedure. This step can be automated with, for example, a laser abrader automatically removing portions of the resistive paths 14 and 18 until the ratio of each of the paths 14 and 18 to the path 16 reached a predetermined level, automatically stopping the abrading operation. Each of the fixed resistive paths 14 and 18 contains a wide portion 17 and a narrow portion 19, the wide portion abraded at 77 to increase the resistance of that particular resistive path.
Compactness of the voltage divider is achieved by the symmetric placement of each of the resistive paths 14 and 18 on either side of the arcuate resistive path 16, each of the fixed resistive paths disposed around the locator holes 34. As best seen in FIG. 4, the driver 23 and the resistive paths 14 and 18 are compactly placed on substrate 12, the driver 23 overlying approximately one-half the area of the substrate, the resistive paths 14 and 18 disposed on the remaining area of the substrate.
While there has been illustrated and described what is at present considered to be a preferred embodiment of the present invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.