US2782340A

US2782340A - Regulated bias voltage supply

Info

Publication number: US2782340A
Application number: US400963A
Authority: US
Inventors: Siskel Manuel
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1953-12-29
Filing date: 1953-12-29
Publication date: 1957-02-19
Anticipated expiration: 1974-02-19

Description

Feb. 19, 1957 M. SISKEL REGULATED BIAS VOLTAGE SUPPLY Filed Dec. 1953 IXIfENTOR. MANUEL v SISKE-L A TTOR NE Y and H 2,782,340 REGULATED BIAS VOLTAGE SUPPLY lvianuel Siskel, Camden, N. J5, assignor to Radio Corporation of America, a corporation of Delaware Application December 29, 1953, Serial No. 400,963

7 Claims. on. 3-15-30 This invention relates generally to regulated bias voltage supplies, and more particularly to a regulated bias voltage supply for cathode ray tubes supplied with operatingpotentials from negative output high voltage power supplies. While neither specifically nor eXclusively limited thereto, the regulated bias voltage supply of the present invention'is particularly useful for supplying a fiXed bias voltage at a low impedance for cathode ray tubes in applications where it is necessary to clamp incoming signals to the bias level voltage for D. C. restoration purposes.

There are many instances in the commercial applications of cathode ray tubes where it is either necessary or desirable to apply a grounded or very low voltage to the anode, and'a high negative voltage to the cathode. The grid bias voltage in these, cases is normally obtained from a variable tap on a resistive voltage divider network. In most of these cases, the resistive voltage divider network is in the order of manymegohms so that the grid bias voltage is effectively derived from a relatively very high impedance source. This very high impedance source is objectionable where it is necessary to clamp incoming signals applied to the control grid of the cathode ray tube to the bias voltage level for D. C. restoration purposes, as is usually the case.

It is, therefore, a principal object of the present invention to provide an improved regulated bias voltage power supply at low impedance.

Another object of the present invention is to provide improved means for supplying grid bias voltage at low impedances from a high impedance voltage divider tap.

A further object of the present invention is to provide an improved regulated low impedance bias voltage supply without the need for additional transformers, rectifiers, or filters.

It is still a further object of the present invention to provide an improved low impedance regulated bias voltage power supply which is simple in structure and operation, economical and easy to manufacture, and highly efiicient in use.

These and'further objects of the present invention are attained in an improved regulated bias voltage supply having a high'input impedance and a relatively low output impedance. A regulated bias voltage supply, in accordance with the present invention, is a part of the output voltage of a negative output high voltage power supply. A high resistive voltage divider network is connected across the negative and positive output terminals of the negative output high voltage power supply, and the positive terminal thereof is grounded. A portion of the voltage divider adjacent the negative terminal of the high voltage power supply is maintained at a constant voltage by one or more voltage regulating tubes connected in parallel therewith. A triode and a cathode resistor therefor are also connected in parallel with the portion of the voltage divider maintained at a constant potential. One end of the cathode resistor is connected'to the negative output terimnal of the negative output high voltage power rates Patent supply. The grid of the triode is connected to an adjustable tap on the portion of the resistance of the voltage divider that is maintained at a constant potential. The output of the regulated bias voltage supply is derived from the anode and the cathode of the triode. in practice, the anode of the triode will be connected to the cathode of a cathode ray tube and the cathode of the triode will be connected to the control grid of the cathode ray tube through a grid resistor. Where input signals to the grid of the cathode ray tube are to be restored to the bias level voltage applied to the grid resistor, the anode of the diode is connected to the cathode of the triode. With this arrangement, any tendency causingthe grid voltage applied to the cathode ray tube to rise, which may be caused by an increased positive input signal to the grid of the cathode ray tube, will be offset by an increase in the internal impedance of the triode which, in turn; will tend to decrease the flow of current through the cathode resistor of the triode, thereby maintaining the cathode potential thereof substantially constant. A reverse set of conditions, which may be caused by a high negative signal applied to the input of the cathode ray tube, tending to lower the grid bias, will be offset by a decrease in the variable impedance of the triode, which in turn, will tend to cause more current to flow through the cathode resistor, thereby tendingto restore the cathode voltage of the triode to its .original voltage. p

The novel features of:the present invention, as well as the invention itself, both as to its organization and method of operation will be understood in detail from the following description when considered in connection with the accompanying drawing, which is a scheniaticdiagram of a regulated bias voltage supply, connectedto a cathode ray tube in a manner to supply it with grid bias at a low impedance for D. C. restoration purposes, in accordance with the present invention.

Referring now to the drawing, there is shown a regulated bias voltage supply which derives its energy from, and is a part of, a high voltage power supply 10. The. high voltage power supply 10 may be any one of the conventional unidirectional output voltage types used for. the operation of cathode ray tubes, such as a regulated radio frequency power supply, a fiy-back type power supply, a regulated A. C. type using voltage doubling circuits, and the like, well known in the art. A'positive output terminal 12 of the power supply 10 is connected to a source of reference potential, such as ground, thereby providing a negative output voltage. A negative output terminal 14 of the power supply It) is connected to ground through a high impedancevoltage divider series network 16 comprising a potentiometer 18,

resistors

20 and 22, a potentiometer 24, and a resistor 26, connected in series. Constant voltage means such as three voltage regulating tubes 28, 30 and 32, connected in series, are connected between the negative terminal 14 of the power supply 10 and the junction between the resistors 2i} and 22. The voltage regulating tubes 28, 30 and 32, which may be of the neon type or the like, serve to maintain the voltage across a portion of the voltage divider network 16; namely, across the potentiometer 18 and the resistor 20, at a constant potential. One output terminal 34- of the regulated bias voltage supply is connected to the negative terminal 14 of the power supply 10 through a 'resistor'36. The output terminal 3 3 of the regulated bias voltage supply is connected to the junction between the resistors 2d and 22, and to an anode of a variable impedance electron discharge device ill, such as a triode tube. The cathode of the tube 44} is connected to the output terminal 3 and the control grid is connected to the movable tap of the potentiometer 18.

Means for maintaining the bias voltage across the

terminals

34 and 38 substantially constant will be eX- plained in connection with the operation of a cathode ray tube 42 wherein it is necessary to clamp incoming signals to the fixed voltage level at the terminal 34, for D. C. restoration purposes. The movable tap of the potentiometer 24 is connected to a focus anode 44 of the cathode ray tube 42. An accelerating anode 46 of the cathode ray tube 42 is connected to ground. The cathode of the cathode ray tube is connected to the output terminal 38 of the bias voltage supply, and the control grid 48 of the cathode ray tube 42 is connected to the output terminal 34 of the bias voltage supply, through a grid resistor 50. Input signals are applied to the control grid 48 of the cathode ray tube 42 through a coupling capacitor 52, and are restored to the bias voltage level of the output terminal 34 by clamping means such as a diode 54. The anode of the diode 54 is connected to the output terminal 34, and the cathode of the diode 54 is connected to the grid 48 of the cathode ray tube 42. The diode 54 may be reversed for limiting signals in an opposite polarity.

The operation of the regulatory action of the bias voltage supply, in accordance with the present invention, will now be described in connection with the operation of the cathode ray tube under conditions which tend to cause the bias voltage at the output terminal 34 to vary. The voltage applied to the control grid of the variable impedance tube 40 in adjusted so that the tube 40 conducts suflicient current to maintain the voltage at its cathode, that is, the voltage at the output terminal 34, at a desired bias voltage level, without any input signals applied to the grid 48 of the cathode ray tube 42. It will be noted that the anode of the variable impedance tube 40 is maintained at a substantially constant potential with respect to the negative terminal 14 of the power supply because of the regulatory action of the voltage regulating tubes 28, 30 and 32. Let it now be assumed that a large positive input signal is applied to the grid 48 of the cathode ray tube 42. This positive signal will cause the cathode ray tube 42 to conduct heavily. Conventional current may be said to flow from ground through the cathode ray tube 42 to its cathode, thence through the variable impedance tube 40, the cathode resistor 36, to the negative terminal 14 of the power supply 10. The increased current flow through the cathode resistor 36 will tend to increase the voltage at the output terminal 34. The control grid of the variable impedance tube 40, however, is maintained substantially constant since the portion of the voltage divider 16 connected in parallel with the voltage regulating tubes 28, 30 and 32 is maintained substantially constant. The tendency for the cathode of the variable impedance tube 40 to go positive has the same effect as increasing the negative bias of the variable impedance tube 40, thereby causing the latter to decrease conduction therethrough, and also through the cathode resistor 36. Thus, it is seen that a tendency for the voltage at the output terminal 34 to go positive, caused by the positive-going signal applied to the grid 48 of the cathode ray tube 42, is offset by the tendency of the variable impedance tube 40 to increase and thereby decrease the current through the cathode resistor 36, whereby the voltage at the output terminal 34 is maintained substantially constant.

In the case where a strongly negative signal is applied to the control grid 48 of the cathode ray tube 42, there is a tendency for the voltage at the output terminal 34 to decrease in a negative direction because of decreased conduction through the cathode ray tube 42. Since the control grid of the variable impedance tube 40, however, is maintained at a constant potential, the tendency for the cathode of the tube 40 to go negative has the same effect as increasing the positive bias of the variable impedance tube 40, resulting in a greater conduction therethrough. An increased current through the variable impedance tube 40 will cause more current to flow 4 through the cathode resistor 36, thereby increasing the potential at the output terminal 34, and ofisetting any tendency of the voltage at the terminal 34 to drop.

Thus, it is seen that the shunted grid resistor 50 is connected to a point, the output terminal 34, that maintains a substantially constant voltage determined by the setting of the variable tap on the potentiometer 13. Since the control grid 48 of the cathode ray tube 42 is connected to a substantially fixed voltage at the output terminal 34, through the parallel circuit comprising the grid resistor 5t and the diode 54, the effect is the same as connecting the grid resistor 50 and the diode 54 to a very low resistance in order to obtain effective D. C. restoration. In accordance with the bias voltage supply of the present invention, the grid resistor 50 may be relatively large compared with the effective resistance of the bias supply, so that the ratio of grid resistance to bias supply resistance may be easily made as high as 1000, whereby D. C. restoration may be easily accomplished. It is noted that without the regulated bias voltage circuit of the present invention, if the bias voltage for the cathode ray tube 42 were taken directly from the voltage divider network 16, a very high resistance, as is usually the case in prior art methods, D. C. restoration would not be as satisfactorily accomplished because of this high resistance. This follows from the premise that good D. C. restoration may be had When the path from the grid 48 of the cathode ray tube 42 to the negative terminal 14 is one of high resistance when the diode 54 is non-conducting, and one of relatively low resistance when the diode 54 is conducting.

There has been shown and described, in accordance with the objects of the present invention, a bias voltage power supply for a cathode ray tube. The input to the bias voltage power supply is a high impedance voltage source derived from a portion of a conventional voltage divider network of a high voltage power supply. The output of the bias voltage supply presents a relatively low impedance whereby input signals applied to the grid of the cathode ray tube may be restored to a substantially constant regulated voltage at the output of the bias voltage supply.

What is claimed is:

l. A regulated bias voltage supply comprising a source of unidirectional voltage, a voltage divider network connected across said source, means connected across a portion of said network to maintain a constant potential across said portion, a variable impedance tube having an anode, a grid and a cathode, a resistor connected between said cathode and one end of said portion, said anode being connected to the other end of said portion, said grid being connected to a point on said portion, and output means to derive a regulated bias voltage output across said anode and said cathode.

2. A regulated bias voltage supply comprising a source of unidirectional voltage, a voltage divider network connected across said source, means connected across a portion of said network to maintain a constant potential across said portion, a variable impedance tube having an anode, a grid and a cathode, a resistor connected between said cathode and one end of said portion, said anode being connected to the other end of said portion, said grid being connected to a point on said portion, and output means to derive a regulated bias voltage output across said anode and said cathode, said one end of said portion being connected to the negative side of said source of unidirectional voltage.

3. A regulated bias voltage supply comprising a source of unidirectional voltage, a voltage divider network connected across said source, means connected across a portion of said network to maintain a constant potential across said portion, a variable impedance tube having an anode, a grid and a cathode, a resistor connected between said cathode and one end of said portion, said anode being connected to the other end of said portion, said grid being connected to a point on said portion, and output means to derive a regulated bias voltage output across said anode and said cathode, said source being a negative output voltage power supply, and said one end of said portion being connected to the negative side of said source.

4. Means for providing a cathode ray tube having a grid and a cathode with a regulated grid bias voltage, said means comprising a source of unidirectional voltage, a voltage divider network connected across said source, constant voltage means connected across a portion of said network, a circuit comprising a variable impedance device and a resistor connected in series therewith, said circuit being connected in parallel with said portion and said constant voltage means, said device having an electrode connected to a point on said portion, and output means to derive said grid bias voltage across said device.

5. Means for providing a cathode ray tube having a grid and a cathode with a regulated grid bias voltage, said means comprising a source of unidirectional voltage, a voltage divider network connected across said source, constant voltage means connected across a portion of said network, a circuit comprising a variable impedance device and a resistor connected in series therewith, said circuit being connected in parallel with said portion and said constant voltage means, said device having an electrode connected to a point on said portion, and output means to derive said grid bias voltage across said device, one end of said portion and one end of said resistor being connected to the negative side of said source of unidirec tional voltage.

6. Means for providing a cathode ray tube having a grid and a cathode with a regulated grid bias voltage, said means comprising a source of unidirection voltage, a voltage divider network connected across said source, constant voltage means connected across a portion of said network, a circuit comprising a variable impedance device and a resistor connected in series therewith, said circuit being connected in parallel with said portion and said constant voltage means, said device having an electrode connected to a point on said portion, output means to derive said grid bias voltage across said device, one end of said portion and one end of said resistor being connected to the negative side or" said source of unidirectional voltage, and a grid resistor connected between said grid and the other end of said first-mentioned resistor, said cathode being connected to said device.

7. Means for providing a cathode ray tube having a grid and a cathode with a regulated grid bias voltage in a manner to clamp signals applied to said grid to the level' of said grid bias voltage, said means comprising a source of unidirectional voltage, a voltage divider network connected across said source, constant voltage means connected across a portion of said network, a circuit comprising a variable impedance device and a resistor connected in series therewith, said circuit being connected in parallel with said portion and said constant voltage means, said device having an electrode connected to a point on said portion, output means to derive said grid bias voltage across said device, one end of said portion and one end of said resistor being connected to the negative side of said source of unidirectional voltage, a grid resistor connected between said grid and the other end of said firstrnentioned resistor, said cathode being connected to said device, and a diode connected across said grid resistor.

References Cited in the file of this patent UNITED STATES PATENTS 2,219,188 Kuehni Oct. 22, 1940 2,394,891 Bowie Feb. 12, 1946 2,465,406 Taylor Mar. 29, 1949 2,470,048 Norton May 10, 1949 2,559,078 Kell July 3, 1951 2,629,840 Weiss Feb. 24, 1953