US3836840A

US3836840A - Voltage regulator with saturation protection

Info

Publication number: US3836840A
Application number: US00388252A
Authority: US
Inventors: H Radloff
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1973-08-14
Filing date: 1973-08-14
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17
Also published as: CA1030256A

Abstract

A voltage regulator having a series regulator transistor with a potential threshold device for preventing saturation. The potential threshold device includes a voltage divider and diode connected between the input electrode and a control device connected to the control electrode of the series regulator transistor whereby a control voltage applied to the control electrode is decreased when the potential difference between the input and control electrodes decreases below a threshold level. A pincushion correction waveform is also applied to the control electrode to modulate the regulated voltage with a pincushion correction signal.

Description

XR steam/540 Unlted States Patent 1 1 3,836,840 Radloff Sept. I7, 1974 [5 VOLTAGE REGULATOR WITH 3,566,158 2/1971 Paine et al. 307/253 SATURATION PROTECTION 3,610,963 10/1971 Higgins 307/253 X [75] Inventor: John Radloff, Williamsville, Primary Examiner A. D Pellinen [73] Assignee: GTE Sylvania Incorporated,

Stanford, Conn.

[22] Filed: Aug. 14, 1973 [21] Appl. No.: 388,252

[52] US. Cl. 323/22 T, 178/DIG. 11, 321/16, 323/39 [51] Int. Cl. G05f 1/56 [58] Field of Search 178/73 R, 7.5 R, DIG. 11; 307/253, 296, 297; 321/16; 323/16, 22 T, 22 Z, 39

[56] References Cited UNITED STATES PATENTS 2,888,633 5/1959 Carter 323/39 UX 3,246,170 4/1966 Olshan 323/22 Z 3,514,690 5/1970 Quiros 323/39 X SIGNAL Attorney, Agent, or Firm-Norman J. OMalley; Robert E. Walrath; Cyril A. Krenzer [57] ABSTRACT A voltage regulator having a series regulator transistor with a potential threshold device for preventing saturation. The potential threshold device includes a voltage divider and diode connected between the input electrode and a control device connected to the control electrode of the series regulator transistor whereby a control voltage applied to the control electrode is decreased when the potential difference be-- tween the input and control electrodes decreases below a threshold level. A pincushion correction waveform is also applied to the control electrode to modulate the regulated voltage with a pincushion correction signal.

8 Clairns, 2 Drawing Figures VIDEO RECEIVER CHANNEL I8 SYNCHRONIZING VERTICAL CHANNEL OUTPUT 26 HORIZONTAL OUTPUT VIVZ VOLTAGE REGULATOR WITH SATURATION PROTECTION BACKGROUND OF THE INVENTION This invention relates to voltage regulators and more I particularly to voltage regulators utilizing a series regulator transistor for television receivers. Series voltage regulators of the type typically used in television receivers have a series regulator transistor connected between a source of unregulated voltage and a source of regulated voltage. The control voltage is typically derived from an adjustable source of reference voltage. If the unregulated voltage decreases sufficiently such that the collector and base voltage of the series regulator transistor become approximately equal, the series regulator transistor will saturate. Since the series regulator transistor provides some filtering of the voltage as well as regulation, saturation of the series regulator transistor will cause loss of filtering and loss of regulation.

In some television receivers the voltage regulator which supplies voltage to the horizontal output circuitry is utilized for side pincushion correction. A pincushion correction signal derived from the vertical output circuitry is utilized to modulate the regulated voltage thereby modulating the voltage for the horizontal output circuitry. If the series regulator transistor saturates, the side pincushion correction will be lost thereby cuasing distortion of the deflection signals and deleterious effect on the image displayed on the cathode ray tube.

Known techniques for overcoming the saturation of the series regulator transistor involve the use of expensive and/or complex circuitry and/or devices. For example, many television receivers include an expensive and bulky power transformer which steps-up the line voltage.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to obviate the above-noted and other disadvantages of the prior art.

It is a further object of this invention to provide an improved series voltage regulator.

It is a further object of this invention to provide a voltage regulator incorporating protective circuitry to prevent saturation of a series regulator transistor.

It is a further object of this invention to provide a voltage regulator wherein the regulated voltage is modulated by a pincushion correction signal.

These and other objects and advantages are achieved in one aspect of this invention in a voltage regulator having a series regulator transistor, a control means, and a potential threshold means. The series regulator transistor has an input electrode connected to a source of unregulated voltage, an output electrode, and a control electrode. The control means is connected to the control electrode for providing a control voltage to the series regulator transistor. The potential threshold means is connected between the input electrode and the control means for preventing saturation of the series regulator transistor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block and schematic diagram of the preferred embodiment of the invention; and

FIG. 2 is a waveform diagram to aid in explaining the operation of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

In FIG. 1 typical circuitry found in a television receiver is illustrated in a block diagram, and a power supply incorporating a voltage regulator in accordance with the invention is illustrated schematically. An antenna l0 intercepts transmitted television signals which are coupled to a signal receiver 12. Signal receiver 12 processes the received signal to provide the audio portion thereof to an audio channel 14, the video portion to a video channel 16, and the synchronizing portion to a synchronizing channel 18. Video channel 16 provides a video signal to an image display device illustrated as a cathode ray tube 20. In a color television receiver video channel 16 provides luminance and chrominance signals or color signals to cathode ray tube 20. Synchronizing channel 18 includes typical circuitry for generating signals at the vertical and horizontal deflection rates synchronized to the received television signal. A first output of synchronizing channel 18 is coupled via vertical output circuitry 22 to vertical deflection windings of a yoke 24 associated with cathode ray tube 20. A second output of synchronizing channel 18 is coupled via horizontal output circuitry 26 to horizontal deflection windings of yoke 24. Vertical output circuitry 22 and horizontal output circuitry 26 comprise first and second deflection waveform generators. Horizontal output circuitry 26 also includes voltage generating circuitry such as that used for generating the high voltage and focus voltage for cathode ray tube 20 and supply voltages V, and V Input terminals 28 are adapted to be connected to a suitable source of alternating voltage such as line voltage. One of terminals 28 is connected by an on-off switch 30 in series with a circuit breaker 32 to a rectifier illustrated as a diode 34. A capacitor 36 is connected in parallel with diode 34 between circuit breaker 32 and a lead 40. Rectifier 34 provides an unregulated DC voltage on lead 40 and accordingly comprises a source of unregulated voltage. Lead 40 is connected by a current limiting resistor 42 to a junction 44. Junction 44 is connected by a filter capacitor 46 to a common conductor illustrated as ground. Junction 44 is further connected by a current limiting resistor 48 to an input electrode illustrated as the collector of a series regulator transistor 50. Transistor 50 has an output electrode or emitter connected to a lead 52 on which appears a regulated voltage B+. Lead 52 is connected by a filter capacitor 54 to ground and by parallel connected

resistors

56 and 58 to the collector of transistor 50. Lead 52 is further connected to horizontal output circuitry 26 to provide supply voltage thereto.

A voltage source illustrated as a terminal 60, which can be source V derived from horizontal output circuitry 26, is connected by a resistor 62 in series with a zener diode 64 to ground. The resistive element of a potentiometer 66 and a series connected resistor 68 are connected in parallel with zener diode 64.

Components

62, 64, 66, and 68 comprise a source of reference voltage. A tap of potentiometer 66 is connected by series connected

resistors

70, 72, and 74 to a control electrode or base of a driver transistor 76. Transistor 76 has a collector connected by a current limiting resistor 78 to lead 40 and an ouput electrode or emitter connected by a diode 80 to a control electrode of transistor 50. Transistor 76 and its associated circuitry comprises a control means for providing a control voltage to series regulator transistor 50.

An output of vertical output circuitry 22 is connected to an input of a pincushion correction means or circuit 82 which has an output connected to the control means, for example, to the junction of

resistors

72 and 74. Pincushion correction circuitry 82 includes a resistor 84 and a capacitor 86 connected in series between an output of vertical output circuitry 22 and ground. The junction of resistor 84 and capacitor 86 is connected by a capacitor 88 to a base of a transistor 90. The collector of transistor 90 is connected by a resistor 92 to a source of voltage illustrated as a terminal 94 which can be source V derived from horizontal output circuitry 26. Source 94 is further connected by a resistor 96 to the base of transistor 90 which is further connected by a resistor 98 to ground. The emitter of transistor 90 is connected by a resistor 100 to ground. The collector of transistor 90 is connected by a coupling capacitor 102 to the junction of

resistors

72 and 74.

Junction point 44 is connected by a potential threshold means 104 to the control means, for example, to the junction between

resistors

70 and 72. Potential threshold means 104 includes

resistors

106 and 108 connected in series between junction point 44 and ground. A capacitor 110 is connected in parallel with resistor 108. A unidirectional conduction device illustrated as a diode 112 is connected between the junction of

resistors

70 and 72 and the junction of

resistors

106 and 108.

In operation, when terminals 28 are connected to an alternating voltage source and switch 30 is closed, diode 34 rectifies the voltage applied thereto to develop an unregulated voltage on lead 40. The unregulated voltage is coupled through resistor 42 to junction point 44 where it is filtered by capacitor 46. Resistor 42 protects diode 34 from large current surges particularly during turn-on when capacitor 46 is uncharged. The filtered voltage at junction 44 is coupled by current limiting resistor 48 to the collector of regulator transistor 50. Resistor 48 limits the short circuit current through transistor 50 to protect transistor 50 prior to the opening of circuit breaker 32. The control voltage at the base of transistor 50 determines the voltage of the emitter of transistor 50 and hence the voltage of lead 52. Capacitor 54 filters the regulated B+ voltage on lead 52. The B+ voltage on lead 52 is used, for example, as a supply voltage for circuitry in the television receiver such as horizontal output circuitry 26. Resistors S6 and 58 shunt current around transistor 50 to reduce the power dissipation of transistor 50.

The control voltage at the base of transistor 50 is determined by a control means connected thereto. The magnitude of the control voltage is basically determined by the source of reference

voltage including components

62, 64, 66, and 68. Current flows from source 60 through resistor 62 and zener diode 64 to establish a predetermined voltage drop across potentiometer 66 and resistor 68. The tap of potentiometer 66 can be adjusted to vary'the control voltage, and hence,

the B+ voltage on lead 52. The voltage at the tap of potentiometer 66 is coupled through

resistors

70, 72, and 74 to the base of driver transistor 76, and hence, from the emitter of transistor 76 through diode 80 to the base of transistor 50. Accordingly, in normal operation the voltage on lead 52 will be slightly lower than the voltage at the tap of potentiometer 66. In the illustrated embodiment source 60 is derived from horizontal output circuitry 26. Accordingly, the voltage V, depends upon the B+ voltage. In this embodiment V, is preferably of sufficient magnitude so that the control voltage at the base of transistor 50 does not vary with normal bias voltage variations. Alternatively, source 60 can be derived by other means such that it is independent of the B+ voltage.

In the illustrated preferred embodiment the control voltage is modulated by a pincushion correction signal so that the regulated B+ voltage is correspondingly modulated. A signal with a sawtooth waveform is coupled from vertical output circuitry 22 to pincushion circuit 82 which integrates the sawtooth waveform to provide a signal with a generally parabolic waveform 114 illustrated in FIG. 2. In one practical embodiment of the invention, the B+ voltage applied to horizontal output circuitry 26 was modulated with a pincushion correction signal of approximately eight volts peak-topeak.

In normal operation diode 112 of potential threshold means 104 is reverse biased. The unregulated voltage at the collector of transistor 50 is monitored by the voltage

divider comprising resistors

106 and 108. The voltage at the junction of

resistors

106 and 108 is normally higher than the voltage at the junction of resistors and 72 to keep diode 112 reverse biased. If the potential difference between the collector and base of transistor 50 decreases below a threshold level, for example, due to low line voltage or some other cause, transistor 50 will begin to saturate as its collector voltage approaches the magnitude of the control voltage. In the illustrated preferred embodiment, the first noticeable effect will be a distortion of the pincushion correction signal. The signal distortion observed in one practical embodiment is illustrated in FIG. 2 wherein the pincushion waveform was modified as is shown by dashed line 116 when the invention was not used. The distortion of the pincushion correction signal caused an observable deleterious effect on the image displayed on cathode ray tube 20 by causing a wavy pattern to move vertically through the displayed image. If the unregulated voltage at junction point 44, and hence, the voltage at the collector of transistor 50, decreases further, transistor 50 will be driven further into saturation thereby causing loss of filtering and regulation of the B+ voltage on lead 52.

When the voltage at junction point 44 decreases, however, the voltage at the junction between

resistors

106 and 108 also decreases. At a threshold level determined in part by the ratio of

resistors

106 and 108, diode 112 will become forward biased to clamp the voltage at the junction between

resistors

70 and 72 to the voltage at the junction of

resistors

106 and 108. Accordingly, the control voltage at the base of transistor 50 is caused to decrease with or track the unregulated voltage at junction point 44, and hence, the collector voltage of transistor 50. As long as the control voltage remains lower than the unregulated voltage by a predetermined amount, transistor 50 will not saturate and will not distort the pincushion correction signal.

Accordingly, there has been shown an improved voltage regulator wherein saturation of a series regulator transistor is prevented. A voltage regulator in accordance with the invention possesses many advantages as was noted previously without unduly complex, expensive, or bulky circuitry or components and without deleterious effect on the quality of the displayed image on cathode ray tube 20.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. A voltage regulator comprising:

a source of unregulated voltage;

a series regulator transistor having a control electrode, an output electrode, and an input electrode connected to said source of unregulated voltage;

a source of reference direct voltage;

control means connecting said source of reference direct voltage to said control electrode for providing a control voltage to said series regulator transistor; and

potential threshold means connected between said input electrode and said control means for preventing saturation of said series regulator transistor by decreasing said control voltage when the potential difference between said input electrode and said control electrode decreases below a threshold level.

2. A voltage regulator as defined in claim 1 wherein said potential threshold means includes a voltage divider connected to said input electrode and a unidirectional conduction device connected from a junction of said voltage divider to said control means.

3. A voltage regulator as defined in claim 2 wherein said unidirectional conduction device is a diode.

4. A voltage regulator as defined in claim 2 wherein said control means includes a driver transistor having a control electrode connected to said source of reference voltage and to saicf unidirectional conduction device and an output electrode connected to said control electrode of said series regulator transistor.

5. In a television receiver having first and second deflection waveform generators, a voltage regulator comprising:

a source of unregulated voltage;

a series regulator transistor having a control electrode, an output electrode for providing a regulated voltage, and an input electrode connected to said source of unregulated voltage;

a source of reference direct voltage;

control means connected to said source of reference direct voltage and to said control electrode for providing a control voltage to said series regulator transistor; and

potential threshold means connnected between said input electrode and said control means for preventing saturation of said series regulator transistor.

6. A voltage regulator as defined in claim 5 wherein said output electrode is connected to said first deflection waveform generator for providing a voltage thereto and further including pincushion correction means connected to said second deflection waveform generator and to said control means for varying said control voltage with a pincushion correction signal.

7. A voltage regulator as defined in claim 6 wherein said potential threshold means includes a voltage divider connected to said input electrode and a unidirectional conduction device connected from a junction of said voltage divider to said control means for decreasing said control voltage when the potential difference between said input electrode and said control electrode decreases below a threshold level.

8. A voltage regulator as defined in claim 7 wherein said control means includes a driver transistor having an output electrode connected to said control electrode of said series regulator transistor and a control electrode connected to said source of reference direct voltage, to said pincushion correction means, and to said unidirectional conduction device.

Claims

1. A voltage regulator comprising: a source of unregulated voltage; a series regulator transistor having a control electrode, an output electrode, and an input electrode connected To said source of unregulated voltage; a source of reference direct voltage; control means connecting said source of reference direct voltage to said control electrode for providing a control voltage to said series regulator transistor; and potential threshold means connected between said input electrode and said control means for preventing saturation of said series regulator transistor by decreasing said control voltage when the potential difference between said input electrode and said control electrode decreases below a threshold level.

4. A voltage regulator as defined in claim 2 wherein said control means includes a driver transistor having a control electrode connected to said source of reference voltage and to said unidirectional conduction device and an output electrode connected to said control electrode of said series regulator transistor.

5. In a television receiver having first and second deflection waveform generators, a voltage regulator comprising: a source of unregulated voltage; a series regulator transistor having a control electrode, an output electrode for providing a regulated voltage, and an input electrode connected to said source of unregulated voltage; a source of reference direct voltage; control means connected to said source of reference direct voltage and to said control electrode for providing a control voltage to said series regulator transistor; and potential threshold means connnected between said input electrode and said control means for preventing saturation of said series regulator transistor.