CA1040706A - Momentary power supply shutdown system - Google Patents
Momentary power supply shutdown systemInfo
- Publication number
- CA1040706A CA1040706A CA219,057A CA219057A CA1040706A CA 1040706 A CA1040706 A CA 1040706A CA 219057 A CA219057 A CA 219057A CA 1040706 A CA1040706 A CA 1040706A
- Authority
- CA
- Canada
- Prior art keywords
- power supply
- circuit
- capacitor
- resistor
- switch
- 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
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
- H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
- H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
- H04N3/20—Prevention of damage to cathode-ray tubes in the event of failure of scanning
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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
- H02M7/02—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
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/1555—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit
- H02M7/1557—Conversion of ac power input into dc 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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit with automatic control of the output voltage or current
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Rectifiers (AREA)
- Television Receiver Circuits (AREA)
- Details Of Television Scanning (AREA)
- Emergency Protection Circuit Devices (AREA)
- Protection Of Static Devices (AREA)
- Control Of Voltage And Current In General (AREA)
Abstract
MOMENTARY POWER SUPPLY SHUTDOWN SYSTEM
Abstract of the Disclosure A power supply contains a circuit, including a switch de-vice, which responds to a sudden increase in load current and turns the power supply off for a short predetermined time interval. Such an arrangement is useful in a color television display wherein a cathode ray tube subject to arcing is used. Such arcing can be destructive, particularly where a well regulated power supply is used. The shutoff feature permits the arc to clear before power is reapplied.
Abstract of the Disclosure A power supply contains a circuit, including a switch de-vice, which responds to a sudden increase in load current and turns the power supply off for a short predetermined time interval. Such an arrangement is useful in a color television display wherein a cathode ray tube subject to arcing is used. Such arcing can be destructive, particularly where a well regulated power supply is used. The shutoff feature permits the arc to clear before power is reapplied.
Description
Related Patent U.S. Patent 3,838,332 issued September 24, 1974, and assigned to the present assignee, discloses a regulated power supply using an SCR as a combined rectifier and control device. The present invention is useful in such a power supply, particularly where protection against load device arcing is desired.
Background of the Inven~on ; Arcing in a cathode ray tube CCRT) is a well-known phenomenon although the detailed cause is not well enough under-stood to produce a complete cure. Monochrome CRT's arc on occasion, but color CRT's, due to their higher operating potent-ials, tend to arc more frequently. Accordingly, color TV receivers commonly employ an extensive array of spark gaps to act as pro-tective elements for the circuit devices associated with the CRT.
In the manufacture of a CRT, stringent quality control measures are taken in the various processes to avoid the conditions - that lead to arc production. In addition a process known as spot knocking is employed. In this technique a much higher than normal voltage is applied to the finished CRT and this will enhance arcing. Each arc tends to destroy the arc-producing mechanism so that, after a short period of intense arcing at a higher-than ;~ normal voltage, the tube will be substant~ally arc-free at normal ';
.
.
- , - ~ . ,.
104~)706 voltage. While the measures taken during manufacture have reduced arcing to a very lo~ incidence it still occurs, particularly after the CRT has been handled extensively as it is in shipment and/or mounting in a TV receiver.
In conventional TV receivers, the startin~;of an arc will quickly reduce the high voltage, due to poor supply regulation, and the arc will tend to be self-extinguishing. However in modern solid state TV receivers much better high voltage regulation is being achieved in order to produce more satisfactory picture reproduction performance. For example in a conventional switching-type solid state TV deflection circuit, the circuit is regulated to provide deflection that is substantially independent of power line voltage. In some circuits regulation is acoomplished by the use of a regulated low voltage power supply. In either case the high voltage is regulated usually by controlling the deflection circuit. While these modern circuits provide much more satisfact-ory picture performance, they tend to make arcing a more serious problem. In effect, when an arc does occur, the energy discharged is much greater. Under some conditions the regulation is good enough that the arc will be sustained for an extended period. This can be harmful to the CRT as well as to the horizontal deflection and high voltage components. Fast acting circuit breakers can be used to interrupt the applied voltage when the current drawn by the circuit exceeds some predetermined value. However such devices are expensive, difficult to set properly, and are subject to false triggering. In addition they must be reset ma~ually, thereby making them a nuisance.
Summary of the Invention It is an object of the invention to provide a regulated power supply that will sense a sudden large increase in current drain and respond by shutting off momentarily.
It is a further object to provide a regulated power supply ~0407Q6 for a TV receiver in which a CRT arc will be sensed and the power supply turned off long enough toreceive the arc and then be turned back on again.
It is a feature of the invention that the above objects are accomplished by adding a small number of inexpensive components to a known regulated power supply circuit so that very little cost is associated with the invention.
These and other ob~ects and features are achieved in a momentary shutdown circuit for a regulated power supply, aaid power supply including at least one SCR connected as a rectifier between an a-c input source and a smoothing filter, a pulse gener-ator synchronized by said a-c input source and connected to fire said SCR, a reference supply source connected for comparison with said power supply output, a variable pulse delay circuit connected into said pulse generator so as to vary the timing of firing said SCR, said pulse delay connected to sense the difference between the potentials of said power supply and said reference supply and to reduce said delay as said difference decreases, said shutdown circuit comprising:
a storage capacitor having t~o terminals, one terminal of said capacitor being connected to the output of said power supply and the second terminal being connected through a series resistor to a shutdown source of potential independent from said power supply and having a potential value substantially lower than the nominal potential of said power supply, and a unidirectional switch connected between said second ter-minal of said capacitor and a control element of said pulse gener-ator, said switch being connected in a p~larity such that said shutdown source biases said switch to be normally nonconductive but conductive when a sudden drop in power supply voltage is coupled by way of said capacitor to said switch, said switch when conductive acting upon said control element to render said 1~4~1706 pulse generator inactive thereby shutting down the operation of said power supply for a period of time determined by the time constant of said resistor-capacitor combination.
Brief Description of the Drawing~
Figure 1 is a schematic diagram of a prior art circuit;
Figure 2 is a graph showing the operation of the circuit of Figure l;
Figure 3 is a schematic diagram of a circuit employing the invention; and Figure 4 is a schematic diagram showing in greater detail a power supply employing the invention.
Description of the Prior Art Referring to Figure 1, SCR 1 is connected as a half wave rectifier to the a-c input line. This input can be the secondary of a transformer, but in the interests of economy, and if no voltage transformation is re~uired, it is convenient to connect the SCR directly to the 120-volt a-c line. The half-wave rectified output is applied to a conventional filter 2 which smooths the rectifier output to provide a steady d-c output voltage. If the circuit used a simple-diod~e, or if the SCR gate electrode were returned through a suit~ble resistor to the anode, a conventional half-wave rectifier would result. In such a circuit the rectifier would turn on during the rise of the positive excursion of the a-c input voltage and would charge filter capacitor 4 to the peak a-c line voltage. The rectifier would turn off when the a~c input voltage drops to the cathode voltage level. The filter capacitor would discharge until the next positive a-c input ex-cursion whereupon the cycle repeats. Clearly, the d-c output voltage would be a function of the peak input voltage.
By adding the pulse generator 3 to the circuit, the SCR
can be fired when desired by a controlled gate pulse. As shown in Figure 2, the SCR is fired somewhere near the a-c input peak, 1~40706 the firing angle being designated ~. ~ will be located in the range extending from shortly ahead of the 90 point to shortly ahead of the 180 point on the input wave form. This is because the maximum power supply energy capability will occur when the SCR is fired sli~htly ahead of the 90 point on the input wave, and to have any output at all the SCR must be fired ahead of the 180 point. ~he dashed line shows the voltage waveform ~
across the input filter capacitor 4. At ~, when the SCR is fired by a pulse from generator 3, the capacitor will quickly charge along an exponential rise to whatever voltage is present at the SCR anode. Then the capacitor will discharge between positive input alternations until the next firing interval. It can be seen that the capac~tor charge is no longer related to peak line voltage. In addition, the magnitude of charge can easily be controlled or varied by changing the firing angle ~.
As 8hown in Figure 1, the pulse generator is synchronized by connecting it to the a-c input. The generator supplies a pulse, delayed with respect to the a-c input, that will turn the SCR on n in the range of less than ~0 to less than 180. The delay is made variable in response to the difference between the d-c output voltage and a separate fixed d-c reference voltage applied between the indicated terminals. If the d-c output voltage is too low, the delay is reduced so that the SCR fires sooner; this will locate the firing point closer to the a-c input peak. If the d-c output voltage is too high, the delay is increased so that the SCR
; fires later and, therefore, lower down on the a-c input waveform.
By making the firing angle 0 a strong function of d-c output, ;~ close control of the output voltage is obtained. Clearly, the circuit will compensate for input or power line variations as well as load variations.
General Description of the Invention Figure 3 shows the components that are added to the circuit _5_ of Figure 1 to practice the invention and how the power supply is connected to a CRT display.
Capacitor 7 charges through resistor 8 to the difference between the d-c output voltage and the d-c reference voltage.
Thus the cathode of diode 9 will be at the positive potential of the d-c reference voltage. Because the anode of diode 9 is at a substantially lower potential (as will be apparent from the more detailed description of the circuit of Fig. 4), diode 9 will be reverse biased and in its open switch state. For these conditions the circuit will function normally as a regulated power supply.
The power supply operatesi the CRT display circuits 30 which include a high voltage supply 31. The display circuits and high voltage output are connected to CRT 32.
If for some reason, such as an arc in CRT 32, the d-c voltage output drops suddenly so that capacitor 7 will not have time to discharge, the cat:Hod?eof diode 9 can be driven more negative than its anode and it will be driven into its on switch state. This action causes pulse generator 3 to stop supplying pulses to SCR 1 which will then remain off. The d-c output voltage will then continue to fall thereby holding diode 9 conductive until the energy stored in filter 2 is discharged. This means that when a CRT arc occurs the influx of energy to the system is halted and the arc will only trigger the dissipation of the energy stored in the power supply filter, the CRT horizontal deflection circuit and the high voltage supply. Once that energy is dissipated, the arc will be relieved and the circuit restored to normal operation. If - this arc termination were not accomplished, the regulated power supply could drive a considerable quantity of energy into the system possibly damaging the CRT or its associated components.
Once the d-c output voltage has dropped to some low value and capacitor 7 has discharged through resistor 8 to a value that will no longer hold diode 9 in its on switch state, the diode will cease to conduct and the pulse generator will resume its functioning. This will again turn SCR 1 on periodically and filter 2 will again become charged and the system will resume normal ~unctioning. The time constant of capacitor 7 and resistor 8 is established to give the circuit an off interval of about 2 seoonds. This period will be long enough to make sure that any arc will be completely interrupted but is short enough to have only a small effect on TV viewing. Clearly this interval can be selected within wide limits to achieve the desired action.
Many times a single arc occurance will, as described above in ~ackground-of the Invention, destroy the arc-producing mechanism and the system will operate normally after a single interruption cycle. However if the arc-producing mechanism still exists, an arc will develop again and the shutdown sequence repeated. Only in rare cases will the arc-producing mechanism survive several arc ~equences with the interposed shut-down intervals. In the event that the arc-producing mechanism remains present, the shut-down seq~e~ce~ wil} continue to operate until the display is turned off manually.
; 20 Figure 4 is a complete power supply schematic showing how the pulse generator of figure 3 can be implemented using a combined pulse generator-variable delay circuit.
SCR 1 is connected directly to the a-c input and provides rectified d-c output by way of filter 2 which is composed of input filter capacitor 4, output filter capacitor 5, and series filter inductor 6. Under typical conditions, the d-c output voltage may be of the order of 100 volts. Compl-ementary tran-~ sistors 10 and 11 are connected into a well known bistable latch-;~ ing complementary pair configuration. ~ransistor 10, in addition to being part of a latching pair, also acts as a Miller effect delay device. When transistor 10 is turned on from its off state, it will come on slowly due to the Miller effect. After a delay period, its output will become sufficient to turn transistor 11 on and the complementary pair will then rapidly switch on to saturation. This latter turn on action provides a pulse that is coupled by way of coupling capacitor 25, to the SCR so as to fire it. Since the turn on of transistor 10 is synchronized to the a-c input by way of the network consisting of resistors 13 and 18 and diode 12, the SCR firing angle is then controlled by the durationi^~of the Miller effect delay. The delay is in turn cont-rolled by applying tbY way of resistance 17, 1~, 20, 21, 22 and 23) a fraction of the d-c output voltage to the base of transistor 11 to act as a bias or threshold control. As the d-c output voltage varies, the threshold at which the complementary pair switches on will be varied. This action varies the duration of the Miller effejct delay. The sense of this feed-back loop is such that the d-c output voltage will tend to remain nearly constant as will be discussed hereinafter.
A 20-volt reference supply is shown operatingithe delay and switching circuits. In applications where a suitable regulated voltage is available it would be used. If no such regulated voltage is available, the reference can be obtained from any con-venient unregulated source that supplies more than the required value at the lowest a-c line voltage condition. A dropping resis-tor and zener diode having the required voltage rating are con-nected in series across the unregulated source. The voltage present across the zener diode is then used as the reference. If no such unregulated source is available an additional rectifier - diode and filter capacitor combination can be connected to the a-c input line and the above mentioned resistor-zener diode combination connected across the filter capacitor. These latter components, associated with the 20-volt reference supply, are conventional and are not shown in the drawing~.
In the quiescent state when the a-c input is near zero, 1~4~)706 diode 12 is forward biased by eIectron flow due to the 20-volt reference supply. Electrons will ~low from ~round through resistor 13, from the cathode of diode 12 to its anode, and then up through resistor 14 to the positive supply terminal. Resistor 13 is made quite small, about 0.1% of the value of resistor 14, so that the drop across it is negligible. Diode 12 being forward biased will develop about 0.6 volt at the base of transistor 10.
Resistors 15 and 16 are proportioned to apply a positive voltage of about 2 volts to the emitter of transistor 10. Thus, trans-istor 10 will not conduct until its base is more than about 2.7volts positive. For these quiescent conditions transistor 10 will be cut off and its collector will rest at almost 20 volts.
This will apply a high positive potential to the base of tran-sistor 11 through resistor 17 and transistor 11 will be held in its off state. This is a stable state for both transistors~
Resistors 13 and 18 form a voltage divider across the a-c input and are proportioned to apply about 2~ of the input to the cathode of diode 12. This will be about 3.4 peak volts for a 120-~- volt line condition. As the a-c inputs swings from zero toward - 20 its positive peak, at some point along the excursion, diode ~2 will be cut off or reverse biased. When this occurs, the base voltage on transistor 10 will rise toward the positive 20-volt supply because of resistor 14. When this rise exceeds about 2.7 volts, transistor 10 will start to conduct and its collector will .
start to fall toward ground potential. However, as soon as the collector starts to fall, capacitor 29 will couple the fiall back into the base and oppose the change. This circuit configuration is called a Miller-effect circuit. As far as the base of tran-sistor 10 is concerned, the circuit behaves as if a large capacitor ~ere connected between base and ground. This effective capacitor has a value approximately equal to the value of c~pacitor 29 multiplied by the circuit gain of transistor 10. Thus, a _g_ 104~706 relatively small capacitor 29 will act in conjunction with resistor 14 to ~orm a relatively long time constant integrator.
In effect, a .02 microfarad capacitor can be made to act as if it were a 0.4 microfarad capacitor if the transistor circuit gain is only 20, an easily achieved value.
It will be noted that the emitter of transistor 11 is returned to the 20-volt reference. Thus, when its base drops to about 19.3 volts it will begin to conduct. Resistors 17, 19 and 20 are selected, along with the values of voltage divider resistors 21, 22 and 23 so that transistor 11 will be well below cutoff when transistor 10 is cut off. As the collector voltage of transistor 10 falls, at some point the base of transistor 11 will reach the 19.3-volt level. When this occurs and transistor 11 starts to conduct, collector conduction will tend to drive the base of transistor 10 positive. This in turn lowers the ~ollect-or voltage of transistor 10 so as to turn transistor 11 on even harder. This regenerative action terminates the Miller-effect ramp and both transistors are quickly driven into saturation. At this time the collector of transistor 10 will have dropped to about 5 volts. Ramp termination can occur rapidly because resistor 24 is made much smaller than resistor 14 which, in conjunction with the Miller-effect capacitance, established the ramp rate. In practice, the value of resistor 24 is made as about equal to the value of resistor 15. Thus, if résistors 15 and 16 produce a quiescent off state voltage of 2 volts at the emitter of transistor 10, the value will increase to about 5 volts in the saturation or on state.
Thus, when the complementary transistor pair switches on, a positive pulse will appear at the emitter of transistor 10. This pulseL--will~-~ou~ d--^to-~-he`gaté of S~R L~ap~àci"to~''~5,-"the^~eby causing it to fire. As the a-c input continues to fall, a time is reached at which point diode 12 becomes again forward bia~ed and 104~)'706 `
cuts off transistor 10. This, in turn, cuts off transistor 11 because the collector of transistor 10 quickly returns to is 20-volt level where it will remain until the above sequence is repeated on the next positive half of the a-c input cycle.
If, for some reason, such as an increased load, the d-c output voltage were to decrease, it can be seen that a less positive quiescent bias will appear at the base of transistor 11.
This means that less ramp action is needed at the collector of transistor 10 to produce the level at which the complementary transistor pair switches on. This means that an early switching pulse occurs at the emitter of transistor 10. Since firing SCR 1 earlier will produce more d-c output voltage, the output voltage will be increased by the reduced firing angle to compensate for the postulated d-c output voltage reduction.
Conversely, if the d-c output voltage were to rise, for example as a result of reduced loading, a more positive bias will be applied to tran&istor 111 This means that the ramp on the collector of transistor 10 will have to run longer to cause switch-ing. Since the SCR is now fired later and lower on the a-c input waveform, the d-c output voltage will be reduced to compens-ate for the postulated rise.
For a given set of component values the circuit will act to maintain nearly a constant d-c output voltaqe ~alue. It will, in fact, act to maintain a nearly fixed difference between the d-c output voltage and the reference voltage. Thus, it is responsive to variations of a-c input as well as load variations.
As a matter of convenience, such regulators usually include ~; an adjustable element because otherwise each part would have to be held to excessively strict tolerance. In the circuit of Figure 4 resistor 23 is made variable. As this resistor is varied, a variable fraction of the d~c output voltage is supplied to the base of transistor 11. This will vary the length of the ramp needed to drive transistor 11 into conduction and will, therefore, vary the SCR 1 firing angle. For a given set of input conditions resistor 23 can vary the d-c output voltage over a substantial range. The circuit will then act to maintain the d-c output voltage constant at nearly the set value.
The circuit thus far described constitutes the prior art and is disclosed in detail in above-mentioned Patent Number 3,838,322. That application also shows further circuit refinements that enhance power supply performance. These refinements are not shown here because they are not necessary to understand the pre-sent invention which will now be detailed.
Detailed Description of the Invention Components 7, 8 and 9 comprise the elements added to the prior art power supply to practice the invention. Capacitor 7 will charge through resistor 8 to the difference in potential between the 20-volt reference supply and the d-c output voltage. Thus if the power supply were to be set at 100 volts, capacitor 7 would ., ` charge to 80 volts. This would place the cathode of diode 9 at a ` positive 20 volts. Since the anode of diode 12 is connected to ':~
the base of transistor 10 which operates at a positive potential ' of only a few volts, the diode will be biased in its off switching state. Thus for normal operating conditions the circuit behaves as if components 7, 8, and 9 were not present.
If a sudden increase in power supply loading occurs, such as would be produced by an arc in a color CRT operated by the ~; power supply t capacitor 7 will not have time to dis~harge and the voltage change is coupled directly to the cathode of diode 9. If the drop in power supply voltage is sufficient to drive diode 9 into its on switch state the base of transistor 10 will suddenly become connected to capacitor 7. This will drive the base of transistor to negative with respect to its emitter thereby cutting it off. This will halt the pulsing of SCR 1. The elements of filter 2 will then start to discharge and the output voltage will continue to ~all. This falling output will keep diode 9 turned on by way of the action of capacitor 7. Thus the filter section 2 will discharge, the power supply output will be termin-ated, and the causal arc extinguished. As soon as the d-c output drops, capacitor 7 will start to discharge through resistor 8. At some point along the discharge curve, the cathode of diode 9 will be driven to a potential with respect to its anode that will turn it off. The values of resistor 8 and capacitor 7 are selected 10 to have a time constant that will establish a suitable power supply off interval. A Yalue found to be useful is 2 seconds.
Once diode 9 is driven to its off switch state, the pulse generator ; will resume functioning, SCR 1 will again receive pulses, and filter 2 will be recharged to where the regulator action takes s over circuit operation as described above.
A suitable set of component values for the circuit of figure 4 is as follows:
SCR 1 --C107Dl tGeneral Electricl Capacitor 4 --400 microfarads 175 volts Capacitor 5 - 400 microfarads 150 volts Inductor 6 - 0.2 henry ~; Capacitor 7 - 10 microfarads 150 volts Resistor 8 - 100K Ohms ~ Diode 9 - lN456 Transistor 10 - 2N4424 Transistor 11 - 2N5366 . Diode~12 , - lN456 Resistor 13 - lK Ohms Resistor 14 - 910K Ohms :- .
; 30 Resistor 15 - 3.3K Ohms Resistor 16 - 330 Ohms Resistor 17 - 82K Ohms . .~
1~)40706 Resistor 18 - 47K Ohms Resistor 19 - 6.8K Ohms Resistor 20 - 18K Ohms Resistor 21 - 160K Ohms Resistor 22 - 33K Ohms Resistor 23 - 15K Ohms Resistor 24 - 3.3K Ohms - Capacitor 25 - .047 Microfarad The circuit of figure 4 with the above component values functioned with good regulation. With the inception of a ~udden load increase such as would be occasioned by a CRT arc, the out-put voltage was interrupted for a period o~ about 2 seconds.
The invention has been described in detail and a set of component values has been shown to provide suitable performance.
Numerous m~di~i~ationswill occur to a person skilled in the art.
For examp}e, while the invention has been shown in connection with a half-wave line-connected rectifier, transformer operation could be employed and a full wave rectifier could be used. Further, resistor 8 could-be returned to a source of potential other than the 20-volt reference or even a fraction thereof. The lower the potential to which resistor 8 is returned, the more sensitive the .
circuit will be to a drop in d-c output potential. For the ; conditions given a drop in d-c output of slightly less than 20 volts will initiate momentary shutoff. If resistor 8 were return-~- ed to a 10-volt supply (or 1/2 of the 20-volt reference supply) shutoff would occur when a drop of slightly less than 10 volts occurred. It is clear that still further modifications could be `~ made within the scope and intent of the invention. It is intend-~ ed that the invention be limited only by the following claims.
Background of the Inven~on ; Arcing in a cathode ray tube CCRT) is a well-known phenomenon although the detailed cause is not well enough under-stood to produce a complete cure. Monochrome CRT's arc on occasion, but color CRT's, due to their higher operating potent-ials, tend to arc more frequently. Accordingly, color TV receivers commonly employ an extensive array of spark gaps to act as pro-tective elements for the circuit devices associated with the CRT.
In the manufacture of a CRT, stringent quality control measures are taken in the various processes to avoid the conditions - that lead to arc production. In addition a process known as spot knocking is employed. In this technique a much higher than normal voltage is applied to the finished CRT and this will enhance arcing. Each arc tends to destroy the arc-producing mechanism so that, after a short period of intense arcing at a higher-than ;~ normal voltage, the tube will be substant~ally arc-free at normal ';
.
.
- , - ~ . ,.
104~)706 voltage. While the measures taken during manufacture have reduced arcing to a very lo~ incidence it still occurs, particularly after the CRT has been handled extensively as it is in shipment and/or mounting in a TV receiver.
In conventional TV receivers, the startin~;of an arc will quickly reduce the high voltage, due to poor supply regulation, and the arc will tend to be self-extinguishing. However in modern solid state TV receivers much better high voltage regulation is being achieved in order to produce more satisfactory picture reproduction performance. For example in a conventional switching-type solid state TV deflection circuit, the circuit is regulated to provide deflection that is substantially independent of power line voltage. In some circuits regulation is acoomplished by the use of a regulated low voltage power supply. In either case the high voltage is regulated usually by controlling the deflection circuit. While these modern circuits provide much more satisfact-ory picture performance, they tend to make arcing a more serious problem. In effect, when an arc does occur, the energy discharged is much greater. Under some conditions the regulation is good enough that the arc will be sustained for an extended period. This can be harmful to the CRT as well as to the horizontal deflection and high voltage components. Fast acting circuit breakers can be used to interrupt the applied voltage when the current drawn by the circuit exceeds some predetermined value. However such devices are expensive, difficult to set properly, and are subject to false triggering. In addition they must be reset ma~ually, thereby making them a nuisance.
Summary of the Invention It is an object of the invention to provide a regulated power supply that will sense a sudden large increase in current drain and respond by shutting off momentarily.
It is a further object to provide a regulated power supply ~0407Q6 for a TV receiver in which a CRT arc will be sensed and the power supply turned off long enough toreceive the arc and then be turned back on again.
It is a feature of the invention that the above objects are accomplished by adding a small number of inexpensive components to a known regulated power supply circuit so that very little cost is associated with the invention.
These and other ob~ects and features are achieved in a momentary shutdown circuit for a regulated power supply, aaid power supply including at least one SCR connected as a rectifier between an a-c input source and a smoothing filter, a pulse gener-ator synchronized by said a-c input source and connected to fire said SCR, a reference supply source connected for comparison with said power supply output, a variable pulse delay circuit connected into said pulse generator so as to vary the timing of firing said SCR, said pulse delay connected to sense the difference between the potentials of said power supply and said reference supply and to reduce said delay as said difference decreases, said shutdown circuit comprising:
a storage capacitor having t~o terminals, one terminal of said capacitor being connected to the output of said power supply and the second terminal being connected through a series resistor to a shutdown source of potential independent from said power supply and having a potential value substantially lower than the nominal potential of said power supply, and a unidirectional switch connected between said second ter-minal of said capacitor and a control element of said pulse gener-ator, said switch being connected in a p~larity such that said shutdown source biases said switch to be normally nonconductive but conductive when a sudden drop in power supply voltage is coupled by way of said capacitor to said switch, said switch when conductive acting upon said control element to render said 1~4~1706 pulse generator inactive thereby shutting down the operation of said power supply for a period of time determined by the time constant of said resistor-capacitor combination.
Brief Description of the Drawing~
Figure 1 is a schematic diagram of a prior art circuit;
Figure 2 is a graph showing the operation of the circuit of Figure l;
Figure 3 is a schematic diagram of a circuit employing the invention; and Figure 4 is a schematic diagram showing in greater detail a power supply employing the invention.
Description of the Prior Art Referring to Figure 1, SCR 1 is connected as a half wave rectifier to the a-c input line. This input can be the secondary of a transformer, but in the interests of economy, and if no voltage transformation is re~uired, it is convenient to connect the SCR directly to the 120-volt a-c line. The half-wave rectified output is applied to a conventional filter 2 which smooths the rectifier output to provide a steady d-c output voltage. If the circuit used a simple-diod~e, or if the SCR gate electrode were returned through a suit~ble resistor to the anode, a conventional half-wave rectifier would result. In such a circuit the rectifier would turn on during the rise of the positive excursion of the a-c input voltage and would charge filter capacitor 4 to the peak a-c line voltage. The rectifier would turn off when the a~c input voltage drops to the cathode voltage level. The filter capacitor would discharge until the next positive a-c input ex-cursion whereupon the cycle repeats. Clearly, the d-c output voltage would be a function of the peak input voltage.
By adding the pulse generator 3 to the circuit, the SCR
can be fired when desired by a controlled gate pulse. As shown in Figure 2, the SCR is fired somewhere near the a-c input peak, 1~40706 the firing angle being designated ~. ~ will be located in the range extending from shortly ahead of the 90 point to shortly ahead of the 180 point on the input wave form. This is because the maximum power supply energy capability will occur when the SCR is fired sli~htly ahead of the 90 point on the input wave, and to have any output at all the SCR must be fired ahead of the 180 point. ~he dashed line shows the voltage waveform ~
across the input filter capacitor 4. At ~, when the SCR is fired by a pulse from generator 3, the capacitor will quickly charge along an exponential rise to whatever voltage is present at the SCR anode. Then the capacitor will discharge between positive input alternations until the next firing interval. It can be seen that the capac~tor charge is no longer related to peak line voltage. In addition, the magnitude of charge can easily be controlled or varied by changing the firing angle ~.
As 8hown in Figure 1, the pulse generator is synchronized by connecting it to the a-c input. The generator supplies a pulse, delayed with respect to the a-c input, that will turn the SCR on n in the range of less than ~0 to less than 180. The delay is made variable in response to the difference between the d-c output voltage and a separate fixed d-c reference voltage applied between the indicated terminals. If the d-c output voltage is too low, the delay is reduced so that the SCR fires sooner; this will locate the firing point closer to the a-c input peak. If the d-c output voltage is too high, the delay is increased so that the SCR
; fires later and, therefore, lower down on the a-c input waveform.
By making the firing angle 0 a strong function of d-c output, ;~ close control of the output voltage is obtained. Clearly, the circuit will compensate for input or power line variations as well as load variations.
General Description of the Invention Figure 3 shows the components that are added to the circuit _5_ of Figure 1 to practice the invention and how the power supply is connected to a CRT display.
Capacitor 7 charges through resistor 8 to the difference between the d-c output voltage and the d-c reference voltage.
Thus the cathode of diode 9 will be at the positive potential of the d-c reference voltage. Because the anode of diode 9 is at a substantially lower potential (as will be apparent from the more detailed description of the circuit of Fig. 4), diode 9 will be reverse biased and in its open switch state. For these conditions the circuit will function normally as a regulated power supply.
The power supply operatesi the CRT display circuits 30 which include a high voltage supply 31. The display circuits and high voltage output are connected to CRT 32.
If for some reason, such as an arc in CRT 32, the d-c voltage output drops suddenly so that capacitor 7 will not have time to discharge, the cat:Hod?eof diode 9 can be driven more negative than its anode and it will be driven into its on switch state. This action causes pulse generator 3 to stop supplying pulses to SCR 1 which will then remain off. The d-c output voltage will then continue to fall thereby holding diode 9 conductive until the energy stored in filter 2 is discharged. This means that when a CRT arc occurs the influx of energy to the system is halted and the arc will only trigger the dissipation of the energy stored in the power supply filter, the CRT horizontal deflection circuit and the high voltage supply. Once that energy is dissipated, the arc will be relieved and the circuit restored to normal operation. If - this arc termination were not accomplished, the regulated power supply could drive a considerable quantity of energy into the system possibly damaging the CRT or its associated components.
Once the d-c output voltage has dropped to some low value and capacitor 7 has discharged through resistor 8 to a value that will no longer hold diode 9 in its on switch state, the diode will cease to conduct and the pulse generator will resume its functioning. This will again turn SCR 1 on periodically and filter 2 will again become charged and the system will resume normal ~unctioning. The time constant of capacitor 7 and resistor 8 is established to give the circuit an off interval of about 2 seoonds. This period will be long enough to make sure that any arc will be completely interrupted but is short enough to have only a small effect on TV viewing. Clearly this interval can be selected within wide limits to achieve the desired action.
Many times a single arc occurance will, as described above in ~ackground-of the Invention, destroy the arc-producing mechanism and the system will operate normally after a single interruption cycle. However if the arc-producing mechanism still exists, an arc will develop again and the shutdown sequence repeated. Only in rare cases will the arc-producing mechanism survive several arc ~equences with the interposed shut-down intervals. In the event that the arc-producing mechanism remains present, the shut-down seq~e~ce~ wil} continue to operate until the display is turned off manually.
; 20 Figure 4 is a complete power supply schematic showing how the pulse generator of figure 3 can be implemented using a combined pulse generator-variable delay circuit.
SCR 1 is connected directly to the a-c input and provides rectified d-c output by way of filter 2 which is composed of input filter capacitor 4, output filter capacitor 5, and series filter inductor 6. Under typical conditions, the d-c output voltage may be of the order of 100 volts. Compl-ementary tran-~ sistors 10 and 11 are connected into a well known bistable latch-;~ ing complementary pair configuration. ~ransistor 10, in addition to being part of a latching pair, also acts as a Miller effect delay device. When transistor 10 is turned on from its off state, it will come on slowly due to the Miller effect. After a delay period, its output will become sufficient to turn transistor 11 on and the complementary pair will then rapidly switch on to saturation. This latter turn on action provides a pulse that is coupled by way of coupling capacitor 25, to the SCR so as to fire it. Since the turn on of transistor 10 is synchronized to the a-c input by way of the network consisting of resistors 13 and 18 and diode 12, the SCR firing angle is then controlled by the durationi^~of the Miller effect delay. The delay is in turn cont-rolled by applying tbY way of resistance 17, 1~, 20, 21, 22 and 23) a fraction of the d-c output voltage to the base of transistor 11 to act as a bias or threshold control. As the d-c output voltage varies, the threshold at which the complementary pair switches on will be varied. This action varies the duration of the Miller effejct delay. The sense of this feed-back loop is such that the d-c output voltage will tend to remain nearly constant as will be discussed hereinafter.
A 20-volt reference supply is shown operatingithe delay and switching circuits. In applications where a suitable regulated voltage is available it would be used. If no such regulated voltage is available, the reference can be obtained from any con-venient unregulated source that supplies more than the required value at the lowest a-c line voltage condition. A dropping resis-tor and zener diode having the required voltage rating are con-nected in series across the unregulated source. The voltage present across the zener diode is then used as the reference. If no such unregulated source is available an additional rectifier - diode and filter capacitor combination can be connected to the a-c input line and the above mentioned resistor-zener diode combination connected across the filter capacitor. These latter components, associated with the 20-volt reference supply, are conventional and are not shown in the drawing~.
In the quiescent state when the a-c input is near zero, 1~4~)706 diode 12 is forward biased by eIectron flow due to the 20-volt reference supply. Electrons will ~low from ~round through resistor 13, from the cathode of diode 12 to its anode, and then up through resistor 14 to the positive supply terminal. Resistor 13 is made quite small, about 0.1% of the value of resistor 14, so that the drop across it is negligible. Diode 12 being forward biased will develop about 0.6 volt at the base of transistor 10.
Resistors 15 and 16 are proportioned to apply a positive voltage of about 2 volts to the emitter of transistor 10. Thus, trans-istor 10 will not conduct until its base is more than about 2.7volts positive. For these quiescent conditions transistor 10 will be cut off and its collector will rest at almost 20 volts.
This will apply a high positive potential to the base of tran-sistor 11 through resistor 17 and transistor 11 will be held in its off state. This is a stable state for both transistors~
Resistors 13 and 18 form a voltage divider across the a-c input and are proportioned to apply about 2~ of the input to the cathode of diode 12. This will be about 3.4 peak volts for a 120-~- volt line condition. As the a-c inputs swings from zero toward - 20 its positive peak, at some point along the excursion, diode ~2 will be cut off or reverse biased. When this occurs, the base voltage on transistor 10 will rise toward the positive 20-volt supply because of resistor 14. When this rise exceeds about 2.7 volts, transistor 10 will start to conduct and its collector will .
start to fall toward ground potential. However, as soon as the collector starts to fall, capacitor 29 will couple the fiall back into the base and oppose the change. This circuit configuration is called a Miller-effect circuit. As far as the base of tran-sistor 10 is concerned, the circuit behaves as if a large capacitor ~ere connected between base and ground. This effective capacitor has a value approximately equal to the value of c~pacitor 29 multiplied by the circuit gain of transistor 10. Thus, a _g_ 104~706 relatively small capacitor 29 will act in conjunction with resistor 14 to ~orm a relatively long time constant integrator.
In effect, a .02 microfarad capacitor can be made to act as if it were a 0.4 microfarad capacitor if the transistor circuit gain is only 20, an easily achieved value.
It will be noted that the emitter of transistor 11 is returned to the 20-volt reference. Thus, when its base drops to about 19.3 volts it will begin to conduct. Resistors 17, 19 and 20 are selected, along with the values of voltage divider resistors 21, 22 and 23 so that transistor 11 will be well below cutoff when transistor 10 is cut off. As the collector voltage of transistor 10 falls, at some point the base of transistor 11 will reach the 19.3-volt level. When this occurs and transistor 11 starts to conduct, collector conduction will tend to drive the base of transistor 10 positive. This in turn lowers the ~ollect-or voltage of transistor 10 so as to turn transistor 11 on even harder. This regenerative action terminates the Miller-effect ramp and both transistors are quickly driven into saturation. At this time the collector of transistor 10 will have dropped to about 5 volts. Ramp termination can occur rapidly because resistor 24 is made much smaller than resistor 14 which, in conjunction with the Miller-effect capacitance, established the ramp rate. In practice, the value of resistor 24 is made as about equal to the value of resistor 15. Thus, if résistors 15 and 16 produce a quiescent off state voltage of 2 volts at the emitter of transistor 10, the value will increase to about 5 volts in the saturation or on state.
Thus, when the complementary transistor pair switches on, a positive pulse will appear at the emitter of transistor 10. This pulseL--will~-~ou~ d--^to-~-he`gaté of S~R L~ap~àci"to~''~5,-"the^~eby causing it to fire. As the a-c input continues to fall, a time is reached at which point diode 12 becomes again forward bia~ed and 104~)'706 `
cuts off transistor 10. This, in turn, cuts off transistor 11 because the collector of transistor 10 quickly returns to is 20-volt level where it will remain until the above sequence is repeated on the next positive half of the a-c input cycle.
If, for some reason, such as an increased load, the d-c output voltage were to decrease, it can be seen that a less positive quiescent bias will appear at the base of transistor 11.
This means that less ramp action is needed at the collector of transistor 10 to produce the level at which the complementary transistor pair switches on. This means that an early switching pulse occurs at the emitter of transistor 10. Since firing SCR 1 earlier will produce more d-c output voltage, the output voltage will be increased by the reduced firing angle to compensate for the postulated d-c output voltage reduction.
Conversely, if the d-c output voltage were to rise, for example as a result of reduced loading, a more positive bias will be applied to tran&istor 111 This means that the ramp on the collector of transistor 10 will have to run longer to cause switch-ing. Since the SCR is now fired later and lower on the a-c input waveform, the d-c output voltage will be reduced to compens-ate for the postulated rise.
For a given set of component values the circuit will act to maintain nearly a constant d-c output voltaqe ~alue. It will, in fact, act to maintain a nearly fixed difference between the d-c output voltage and the reference voltage. Thus, it is responsive to variations of a-c input as well as load variations.
As a matter of convenience, such regulators usually include ~; an adjustable element because otherwise each part would have to be held to excessively strict tolerance. In the circuit of Figure 4 resistor 23 is made variable. As this resistor is varied, a variable fraction of the d~c output voltage is supplied to the base of transistor 11. This will vary the length of the ramp needed to drive transistor 11 into conduction and will, therefore, vary the SCR 1 firing angle. For a given set of input conditions resistor 23 can vary the d-c output voltage over a substantial range. The circuit will then act to maintain the d-c output voltage constant at nearly the set value.
The circuit thus far described constitutes the prior art and is disclosed in detail in above-mentioned Patent Number 3,838,322. That application also shows further circuit refinements that enhance power supply performance. These refinements are not shown here because they are not necessary to understand the pre-sent invention which will now be detailed.
Detailed Description of the Invention Components 7, 8 and 9 comprise the elements added to the prior art power supply to practice the invention. Capacitor 7 will charge through resistor 8 to the difference in potential between the 20-volt reference supply and the d-c output voltage. Thus if the power supply were to be set at 100 volts, capacitor 7 would ., ` charge to 80 volts. This would place the cathode of diode 9 at a ` positive 20 volts. Since the anode of diode 12 is connected to ':~
the base of transistor 10 which operates at a positive potential ' of only a few volts, the diode will be biased in its off switching state. Thus for normal operating conditions the circuit behaves as if components 7, 8, and 9 were not present.
If a sudden increase in power supply loading occurs, such as would be produced by an arc in a color CRT operated by the ~; power supply t capacitor 7 will not have time to dis~harge and the voltage change is coupled directly to the cathode of diode 9. If the drop in power supply voltage is sufficient to drive diode 9 into its on switch state the base of transistor 10 will suddenly become connected to capacitor 7. This will drive the base of transistor to negative with respect to its emitter thereby cutting it off. This will halt the pulsing of SCR 1. The elements of filter 2 will then start to discharge and the output voltage will continue to ~all. This falling output will keep diode 9 turned on by way of the action of capacitor 7. Thus the filter section 2 will discharge, the power supply output will be termin-ated, and the causal arc extinguished. As soon as the d-c output drops, capacitor 7 will start to discharge through resistor 8. At some point along the discharge curve, the cathode of diode 9 will be driven to a potential with respect to its anode that will turn it off. The values of resistor 8 and capacitor 7 are selected 10 to have a time constant that will establish a suitable power supply off interval. A Yalue found to be useful is 2 seconds.
Once diode 9 is driven to its off switch state, the pulse generator ; will resume functioning, SCR 1 will again receive pulses, and filter 2 will be recharged to where the regulator action takes s over circuit operation as described above.
A suitable set of component values for the circuit of figure 4 is as follows:
SCR 1 --C107Dl tGeneral Electricl Capacitor 4 --400 microfarads 175 volts Capacitor 5 - 400 microfarads 150 volts Inductor 6 - 0.2 henry ~; Capacitor 7 - 10 microfarads 150 volts Resistor 8 - 100K Ohms ~ Diode 9 - lN456 Transistor 10 - 2N4424 Transistor 11 - 2N5366 . Diode~12 , - lN456 Resistor 13 - lK Ohms Resistor 14 - 910K Ohms :- .
; 30 Resistor 15 - 3.3K Ohms Resistor 16 - 330 Ohms Resistor 17 - 82K Ohms . .~
1~)40706 Resistor 18 - 47K Ohms Resistor 19 - 6.8K Ohms Resistor 20 - 18K Ohms Resistor 21 - 160K Ohms Resistor 22 - 33K Ohms Resistor 23 - 15K Ohms Resistor 24 - 3.3K Ohms - Capacitor 25 - .047 Microfarad The circuit of figure 4 with the above component values functioned with good regulation. With the inception of a ~udden load increase such as would be occasioned by a CRT arc, the out-put voltage was interrupted for a period o~ about 2 seconds.
The invention has been described in detail and a set of component values has been shown to provide suitable performance.
Numerous m~di~i~ationswill occur to a person skilled in the art.
For examp}e, while the invention has been shown in connection with a half-wave line-connected rectifier, transformer operation could be employed and a full wave rectifier could be used. Further, resistor 8 could-be returned to a source of potential other than the 20-volt reference or even a fraction thereof. The lower the potential to which resistor 8 is returned, the more sensitive the .
circuit will be to a drop in d-c output potential. For the ; conditions given a drop in d-c output of slightly less than 20 volts will initiate momentary shutoff. If resistor 8 were return-~- ed to a 10-volt supply (or 1/2 of the 20-volt reference supply) shutoff would occur when a drop of slightly less than 10 volts occurred. It is clear that still further modifications could be `~ made within the scope and intent of the invention. It is intend-~ ed that the invention be limited only by the following claims.
Claims (5)
1. A momentary shutdown dircuit for a regulated power supply, said power supply including at least one SCR connected as a rectifier between an a-c input source and a smoothing filter, a pulse generator synchronized by said a-c input source and connec-ted to fire said SCR, a reference supply source connected for comparison with said power supply output, a variable pulse delay circuit connected into said pulse generator so as to vary the timing of firing said SCR, said pulse delay connected to sense the difference between the potentials of said power supply and said reference supply and to reduce said delay as said difference decreases, said shutdown circuit comprising:
a storage capacitor having two terminals, one terminal of said capacitor being connected to the output of said power supply and the second terminal being connected through a series resistor to a shutdown source of potential independent from said power supply and having a potential value substantially lower than the nominal potential of said power supply, and a unidirectional switch connected between said second terminal of said capacitor and a control element of said pulse generator, said switch being connected in a polarity such that said shutdown source biases said switch to be normally nonconduct-ive but conductive when a sudden drop in power supply voltage is coupled by way of said capacitor to said switch, said switch when conductive acting upon said control element to render said pulse generator inactive thereby shutting down the operation of said power supply for a period of time determined by the time constant of said resistor-capacitor combination.
a storage capacitor having two terminals, one terminal of said capacitor being connected to the output of said power supply and the second terminal being connected through a series resistor to a shutdown source of potential independent from said power supply and having a potential value substantially lower than the nominal potential of said power supply, and a unidirectional switch connected between said second terminal of said capacitor and a control element of said pulse generator, said switch being connected in a polarity such that said shutdown source biases said switch to be normally nonconduct-ive but conductive when a sudden drop in power supply voltage is coupled by way of said capacitor to said switch, said switch when conductive acting upon said control element to render said pulse generator inactive thereby shutting down the operation of said power supply for a period of time determined by the time constant of said resistor-capacitor combination.
2. The circuit of claim 1 wherein said switch is a semi-conductor diode.
3. The circuit of claim 2 wherein said shutdown source is obtained from said reference supply.
4. A circuit of claim 2 wherein the time constant of said capacitor and said resistor is adjusted to produce a shutdown duration of about 2 seconds.
5. The circuit of claim 2 wherein the nominal voltage of said power supply is about 100 volts and the momentary shutdown action is triggered in response to a drop in output of about 20 volts.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US447819A US3916288A (en) | 1974-03-04 | 1974-03-04 | Momentary power supply shutdown system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1040706A true CA1040706A (en) | 1978-10-17 |
Family
ID=23777880
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA219,057A Expired CA1040706A (en) | 1974-03-04 | 1975-01-30 | Momentary power supply shutdown system |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US3916288A (en) |
| JP (1) | JPS546442B2 (en) |
| BR (1) | BR7501100A (en) |
| CA (1) | CA1040706A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5512261Y2 (en) * | 1974-11-14 | 1980-03-17 | ||
| US3980821A (en) * | 1975-08-29 | 1976-09-14 | Rca Corporation | Power supply for a television receiver |
| DE2556860A1 (en) * | 1975-12-17 | 1977-06-23 | Standard Elektrik Lorenz Ag | POWER CIRCUIT FOR TELEVISION RECEIVER |
| DE2556863A1 (en) * | 1975-12-17 | 1977-06-23 | Standard Elektrik Lorenz Ag | POWER CIRCUIT FOR TELEVISION RECEIVER |
| US4270157A (en) * | 1977-11-07 | 1981-05-26 | Rca Corporation | Power supply protection circuit |
| US4163926A (en) * | 1978-09-07 | 1979-08-07 | Rca Corporation | Switching regulator for a television apparatus |
| US5764002A (en) * | 1996-07-01 | 1998-06-09 | U.S. Philips Corporation | Over-current protection circuit for use in television horizontal deflection circuits |
| US7193624B2 (en) * | 2003-11-24 | 2007-03-20 | Amtran Technology Co., Ltd. | Display apparatus with power saving capability |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3573598A (en) * | 1969-05-16 | 1971-04-06 | Bell Telephone Labor Inc | Overload protected switching regulator-converter |
| US3590323A (en) * | 1970-01-22 | 1971-06-29 | Udylite Corp | Peak current limiting system |
| JPS5232532B2 (en) * | 1971-12-24 | 1977-08-22 | ||
| JPS4883711U (en) * | 1972-01-13 | 1973-10-12 | ||
| US3743887A (en) * | 1972-03-24 | 1973-07-03 | Itt | Power supply for an electronic pabx |
| US3813580A (en) * | 1973-01-19 | 1974-05-28 | Rca Corp | High voltage protection circuit |
-
1974
- 1974-03-04 US US447819A patent/US3916288A/en not_active Expired - Lifetime
-
1975
- 1975-01-30 CA CA219,057A patent/CA1040706A/en not_active Expired
- 1975-02-24 BR BR1100/75A patent/BR7501100A/en unknown
- 1975-03-04 JP JP2571775A patent/JPS546442B2/ja not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS546442B2 (en) | 1979-03-28 |
| JPS50143056A (en) | 1975-11-18 |
| US3916288A (en) | 1975-10-28 |
| BR7501100A (en) | 1975-12-02 |
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