US3886401A - Apparatus for accelerating cathode heating - Google Patents

Abstract

Apparatus for accelerating the heating of the cathode heater of a cathode ray tube or the like. A first self-heating positive temperature coefficient resistor is interconnected to an electrical power source. Positioned in heat-exchange relationship with the first resistor is a second self-heating positive temperature coefficient resistor. A resistor of substantially fixed resistance is shunt-connected with said second self-heating resistor. These shunt-connected resistors are connected in series with the heater of the cathode across an electrical power source which supplies power of a substantially constant potential in excess of that required to maintain the heater of the cathode at a predetermined temperature. After power is initially supplied to the cathode heater, its potential will be reduced from a level substantially in excess of that required to maintain the heater at the predetermined temperature to a level which maintains the heater at substantially that predetermined temperature.

Description

United States Patent [1 1 Berg [ APPARATUS FOR ACCELERATING CATHODE HEATING [75] Inventor: Peter G. Berg, Norton, Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 1, 1974 [21] Appl. No.: 484,539

[52] US. Cl. 315/94; 315/8; 315/100; 315/107; 315/309; 317/1575; 328/270 {51] Int. Cl. H051) 39/00 [58] Field of Search 315/94, 99, 100, 106, 107, 315/112, 114, 116,119,149, 179,192, 309, 311, 8; 313/153; 328/270; 317/157.5 TV

l l May 27, 1975 Primary ExaminerR. V. Rolinec Assistant ExaminerE. R. LaRoche Attorney, Agent, or Firmlames P. McAndrews; John A. Haug; Edward J. Connors, Jr.

[57] ABSTRACT Apparatus for accelerating the heating of the cathode heater of a cathode ray tube or the like. A first selfheating positive temperature coefficient resistor is interconnected to an electrical power source. Positioned in heat-exchange relationship with the first resistor is a second self-heating positive temperature coefficient resistor. A resistor of substantially fixed resistance is shunt-connected with said second self-heating resistor. These shunt-connected resistors are connected in series with the heater of the cathode across an electrical power source which supplies power of a substantially constant potential in excess of that required to maintain the heater of the cathode at a predetermined temperature. After power is initially supplied to the cathode heater, its potential will be reduced from a level substantially in excess of that required to maintain the heater at the predetermined temperature to a level which maintains the heater at substantially that predetermined temperature.

4 Claims, 4 Drawing Figures 9 T/ p/ g APPARATUS FOR ACCELERATING CATHODE HEATING BACKGROUND OF THE INVENTION This invention relates to apparatus for acceleration of cathode heating and more particularly to apparatus for providing rapid warm-up of the cathode heater of a cathode ray tube such as used in a television receiver or the like.

With the advent of solid-state circuitry in television receivers. the audio or sound portion of the program would be immediately heard but the time period required for the cathode heater of the picture tube to be brought up to its operating temperature delayed the video portion of the program for about seconds or so. In order to reduce this delay of picture presentation, such television receivers were provided with instanton" circuitry which would provide a picture within about I second or so. This was accomplished typically by maintaining a reduced potential across the CRT cathode heater at all times while the receiver was off so that the CRT cathode could be more rapidly warmed up when the receiver was turned on.

While this instant-on circuit functions effectively to reduce the delay in video presentation, it is not without some substantial disadvantages. Not only is there a continuous power drain, which constitutes a serious energy waste, but the hazard of fires from such continuously partially energized television receivers has raised widespread and deep concern.

SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of apparatus for accelerating the heating of the cathodes of CRTs and the like so as to insure warm-up of the typical CRT cathode heater to provide video presentation within about 5-8 seconds, but which has no power drain when the receiver is turned off; the provision of such apparatus which eliminates any fire hazard from continuously partially energized receiver circuitry and which is low in cost and reliable in operation; and the provision of such apparatus which utilizes no electromechanical contacts but employs solid-state devices and provides a smooth application of electrical energy to the cathode heater thereby avoiding thermal shock.

Briefly, apparatus of the present invention includes a first self-heating positive temperature coefficient resistor having a relatively low initial resistance which increases abruptly as its temperature rises above a given level and means for interconnecting it to an electrical power source thereby rapidly to heat it above a given level. A second self-heating positive temperature coefficient resistor is positioned in heat-exchange relationship with the first resistor and it, too, has a relatively low initial resistance which increases abruptly as its temperature rises above a given level. A resistor of substantially fixed resistance is shunt-connected with the second self-heating resistor. Means are provided for interconnecting these shunt-connected resistors in series with the heater of the cathode heater of a CRT or the like across an electrical power source which supplies power of a substantially constant potential but in excess of that required to maintain the cathode heater at a predetermined tempertture. The resistance of the second self-heating resistor is preferably less, and at least not substantially more, than that of the fixed resistor at temperatures below its aforesaid given level but is substantially greater than that of the fixed resistor at temperatures above its aforesaid given level. After power is initially supplied to the cathode heater its potential will be reduced from a level substantially in excess of that required to maintain the heater at its predetermined temperature to a level which maintains the heater at substantially its predetermined temperature as the first and second resistors self-heat thereby to increase and then maintain the second resistor at a temperature above its aforesaid given level, and thus accelerate the heating of the cathode.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a circuit diagram of apparatus of the present invention for accelerating the heating of the cathode of a cathode ray tube;

FIG. 2 is a graphical representation of the voltagetime relationship for various values of applied voltage and shunt resistors utilizing a low resistance load in the apparatus of FIG. 1;

FIG. 3 is a circuit diagram of another embodiment of this invention which performs the additional function of degaussing of the television receiver; and

FIG. 4 illustrates graphically the voltage applied to a CRT cathode heater as a function of time when employing apparatus of this invention.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, a self-heating positive temperature coefficient (PTC) resistor P1 is shown connected across an electrical power source V by means of a switch S and conductive leads. A second selfheating PTC, P2, is shunt-connected with a resistor R of substantially fixed resistance and these two parallelconnected components are serially connected with an electrical load K constituted by a resistance, such as the filament or cathode heater of a CRT or the like, across the electric power source V via switch S.

Self-heating resistors PI and P2 are each conventional PTC resistors, usually in the form of a pill, having a resistivity-temperature curve which is steepsloped above a threshold or anomaly temperature. Such PTC resistors are formed from certain doped barium titanates, or carbon-black loaded cross-linked polyethylenes, etc. They have a relatively low resistance at usual ambient temperatures but after initial energization by a source of electrical power will self-heat and increase their temperature and resistance. Heat will be generated and the resistance will increase rapidly above the anomaly temperature until the heat generated balances the heat dissipated at which time the temperature and resistance stabilize with the resistance many times the initial value. Thus each PTC has a transition from a high heat generating state initially to a low heat generating state at an elevated temperature (e.g., C.-l 35C.) at which it tends to self-regulate. These two PTC resistors are positioned in heat-exchange relationship with each other, such as by securing them to a common heat-conductive body, e.g., as shown in US. Pat. No. 3,307,167.

When the apparatus of this invention is energized by closing switch S, the substantially constant potential of power source V1 is applied across the two parallel circuits respectively constituted by P1 and by P2,R series connected with load K. The potential of V1 is selected to exceed that required to maintain the current through load K at a predetermined level. A typical CRT cath ode heater is designed to be maintained at its predetermined temperature when a voltage of about 6.3V. is applied thereto. The resistance of such a cathode heater when cold is about 2 ohms but rapidly rises to a steadystate value of about 5-7 ohms. PTC resistors are used which have a resistance at the usual ambient room temperatures of about l-2 ohms. The resistance rapidly rises as the unit self-heats above its threshold temperature and has a resistance at its stabilization temperature that is typically in the order of about 40-200 or more ohms at voltages in the order of l 5V. as used in this example. A value of R is chosen so that the initial resistance of P2 is not substantially more than that of R. Preferably R has a resistance that somewhat exceeds that of P2 at ambient.

Referring now to FIG. 2, the operation of the apparatus of this invention is illustrated using a 7 ohm resistor as the load, a 120C. PTC resistor as P1 and an 80C. PTC resistor as P2. Curve A represents the voltage applied across the 79. load where R is lO.lQ and V1 is 15.8V. It will be noted that after initial energization the voltage across the load drops from a little more than l3V. to about 6.3 volts in somewhat less than 5 seconds, thus applying an initially high power level to the load but smoothly effecting a transition to a desired level of 6.3V. Curve B illustrates the voltage applied across the 79 load where V is 126V. and R 71'), while curve C represents the results where V, is 10V. and R is 4.49. In each instance curves B and C show decreases from initial higher voltage levels to about 6.3V. after about 5-6 seconds.

FIG. 4 illustrates the reduction in potential across the filament or cathode heater of a typical CRT connected as load K in the circuit of FIG. 1 where R is 79, V1 is 15.8 v.d.c. (curve E) and 12.6 v.d.c. (curve F), P1 is a 120C. pill, and P2 is an 80C. pill with a resistance of [.20 at ambient. It will be noted that, because of the lower cathode heater resistance when cold, the voltage across the heater initially rises as the cathode heater temperature and resistance rise, then as the cathode heater resistance stabilizes at its S-Jfl level, this voltage peaks and decreases to the desired level of about 6.3V. at which level the heater of the CRT cathode will be maintained at its desired temperature. thus providing accelerated heating of the cathode so that a picture will be provided in about 5-7 seconds after turn-on. It will be noted that the transition of voltage from that initially applied to the reduced but normal level is always smooth in contradistinction to that which would occur if switching were employed to reduce an initial high level to the steady-state operating level.

While PTC resistor P1 preferably has a somewhat higher stabilization temperature, it is to be understood that similar PTC pills having the same temperatures of stabilization may be used. In either event it will be noted that PI, the heater pill, by being connected across the entire potential of V, will self-heat more rapidly than will P2. Thus P1 supplies a substantial heat input to P2 and causes it to increase its temperature and resistance more rapidly than it would if it was heated only by its own self-heating. It will also be noted that more complex typical time delay circuitry is entirely eliminated and only inexpensive conventional PTC pills and standard fixed resistors are employed in the apparatus of this invention.

FIG. 3 illustrates another embodiment of this inven- 5 tion where Pl performs a second function. In this appa ratus PI is series connected with a conventional degausser coil D of the color television receiver, and a second voltage V2 is applied to P1 and D through a second set of contacts of a double-pole switch S1. Usually line voltage of about 118V. is utilized for V2 so that for a brief initial few seconds after closing of S1 relatively high voltage is applied across coil D (which typically has an impedance of 5-1 ID) to effect degaussing. Very rapidly, however, the fast rising temperature and resistance of P1 reduce the voltage across D and the current so that it is substantially deenergized during continued operation of the television receiver. Upon turning off the receiver, P1 and P2 cool so that after a very brief period, reactuation of S1 will again effect accelerated heating of the cathode of the CRT and degaussing of the receiver when switch S is reclosed.

It will also be noted that P2 will be held at an elevated temperature which is a function of the stabilization temperature of P1 and the coefficient of heat transfer therebetween as well as the dissipation characteristics. Thus, if a 120C. or 135C. PTC pill is utilized for P1. the temperature of P2 may be held at a temperature higher than that at which it would stabilize if no heat were supplied from P1. For example, if P2 were an 80C. pill and P1 were a lC. or l35C. pill the steady-state temperature of P2 may be 95l00C. or even higher and thus provide a resistance greater than what it would provide at its own stabilization temperature of 80C.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for accelerating the heating of the cathode heater ofa cathode ray tube or the like comprising:

a first self'heating positive temperature coefficient resistor having a relatively low initial resistance which increases abruptly as its temperature rises above a given level;

means for interconnecting said resistor to an electrical power source thereby rapidly to heat it above said given level;

a second self-heating positive temperature coefficient resistor positioned in heat-exchange relationship with said first resistor and having a relatively low initial resistance which increases abruptly as its temperature rises above a given level;

a resistor of substantially fixed resistance shuntconnected with said second self-heating resistor; and

means for interconnecting said shunt-connected resistors in series with the heater of said cathode across an electrical power source adapted to supply power of a substantially constant potential in excess of that required to maintain the heater of said cathode at a predetermined temperature.

the resistance of the second self-heating resistor being not substantially more than that of the fixed resistor at temperatures below its aforesaid given level but substantially greater than that of the fixed resistor at temperatures above its aforesaid given level, whereby after power is initially supplied to the cathode heater its potential will be reduced from a level substantially in excess of that required to maintain the heater at said predetermined temperature to a level which maintains the heater at substantially said predetermined temperature as the first and second resistors self-heat thereby to increase and then maintain said second resistor at a temperature above its aforesaid given level. 2. Apparatus as set forth in claim I wherein the first self-heating resistor has a higher temperature at which its resistance stabilizes than has the second self-heating resistor.

3. Apparatus as set forth in claim 1 wherein the first self-heating resistor is series-connected with a degaussing coil across the first mentioned said electrical power source, and which includes switching means for concurrently energizing the first and second self-heating resistors from respective electrical power sources thereby initially to energize the degaussing coil for a brief period of time while the first self-heating resistor rapidly heats and raises the temperature of the second self-heating resistor.

4. Apparatus as set forth in claim I wherein both the first mentioned and second mentioned said electrical power sources are constituted by a single common power source.

Claims (4)

1. Apparatus for accelerating the heating of the cathode heater of a cathode ray tube or the like comprising: a first self-heating positive temperature coefficient resistor having a relatively low initial resistance which increases abruptly as its temperature rises above a given level; means for interconnecting said resistor to an electrical power source thereby rapidly to heat it above said given level; a second self-heating positive temperature coefficient resistor positioned in heat-exchange relationship with said first resistor and having a relatively low initial resistance which increases abruptly as its temperature rises above a given level; a resistor of substantially fixed resistance shuntconnected with said second self-heating resistor; and means for interconnecting said shunt-connected resistors in series with the heater of said cathode across an electrical power source adapted to supply power of a substantially constant potential in excess of that required to maintain the heater of said cathode at a predetermined temperature; the resistance of the second self-heating resistor being not substantially more than that of the fixed resistor at temperatures below its aforesaid given level But substantially greater than that of the fixed resistor at temperatures above its aforesaid given level, whereby after power is initially supplied to the cathode heater its potential will be reduced from a level substantially in excess of that required to maintain the heater at said predetermined temperature to a level which maintains the heater at substantially said predetermined temperature as the first and second resistors self-heat thereby to increase and then maintain said second resistor at a temperature above its aforesaid given level.

2. Apparatus as set forth in claim 1 wherein the first self-heating resistor has a higher temperature at which its resistance stabilizes than has the second self-heating resistor.

3. Apparatus as set forth in claim 1 wherein the first self-heating resistor is series-connected with a degaussing coil across the first mentioned said electrical power source, and which includes switching means for concurrently energizing the first and second self-heating resistors from respective electrical power sources thereby initially to energize the degaussing coil for a brief period of time while the first self-heating resistor rapidly heats and raises the temperature of the second self-heating resistor.

4. Apparatus as set forth in claim 1 wherein both the first mentioned and second mentioned said electrical power sources are constituted by a single common power source.

Images