US2753511A

US2753511A - Power supply

Info

Publication number: US2753511A
Application number: US472107A
Authority: US
Inventors: Spurgeon H Buder
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1954-11-30
Filing date: 1954-11-30
Publication date: 1956-07-03
Anticipated expiration: 1973-07-03

Description

5. H. BUDER POWER SUPPLY July 3, 1956 Filed NOV 30, 1954 m 40/10 CU/PAE/VT ///v ma) 6 6 4 2 Yk E3 Q l k s INVENTOR. 5H/R6t'0/V b. 500.0?

HTTOIP/Yfy United States Patent POWER SUPPLY Spurgeon H. Buder, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November 30, 1954, Serial No. 472,107 7 Claims. Cl. 323-22 This invention relates generally to power supplies, and more particularly to a regulated power supply of the type that will provide a substantially constant voltage for loads up to a predetermined load current and a substantially constant current for loads in excess of the predetermined load current. While neither specifically nor exclusively limited thereto, the power supply of the present invention is particularly useful for supplying power to current-sensitive equipment, such as a Graphechon storage tube, that may be damaged by current in excess of a predetermined amount.

It has been proposed to supply a load with a substantially constant voltage by employing a power supply wherein a source of unregulated voltage is connected in series with a series regulator tube and the load; and feedback means are provided to vary the impedance of the series regulator tube to hold the voltage across the load substantially constant. While such a conventional power supply will provide a load with rated current at a substantially constant voltage, it may provide an excessive amount of current under conditions of overloading. This occurs because the output voltage with excessive loads is not dropped quickly enough with increases in the load beyond a predetermined value. For example, the usual regulated power supply that will provide a Graphechon storage tube with an operating voltage of 9 kilovolts at 1 milliampere may supply twice this current at substantially the same voltage when the Garphechon is overloaded. Such an overloading, however, may burn the target of the Graphechon tube and thereby seriously damage it. Also, conventional regulated power supplies of the type described present a danger to personnel, and possible damage to the regulator circuit of the power supply, in cases of accidental overloading or short circuits.

Accordingly, it is the principal object of the present invention to provide an improved regulated power supply that will overcome the aforementioned disadvantages.

Another object of the present invention is to provide an improved regulated power supply that will provide a substantially constant output voltage for loads of a predetermined current value, and a substantially constant current for loads in excess of this predetermined current value.

=.A further object of the present invention is to provide an improved regulated power supply that will protect personnel in the event of accidental overloads or short circuits.

It is still a further object of the present invention to provide an improved power supply having a novel regulating circuit that will prevent damage to sensitive utilization equipment, and will also prevent damage to the regulator circuit per se in cases of accidental overloading of the power supply.

A still further object of the present invention is to provide an improved regulated power supply of the type described that is simple in construction and operation,

ICC

These and, perhaps, further objects of the present invention are attained in an improved regulated power supply adapted to provide a predetermined voltage up to a predetermined amount of load current, and a very sharp decrease in voltage with load currents that would normally be in excess of the predetermined amount. In a preferred embodiment of the invention a series regulator triode tube and a cathode resistor therefor are connected in series between the positive terminal of a source of unregulated voltage and the positive output terminal of the regulated power supply. A source of fixed D.-C. voltage is connected between the positive output terminal of the power supply and the cathode of the series regulator tube through a diode. Means are also provided to feed back a sample of the output voltage of the power supply to the control grid of the series regulator triode tube. For loads below a predetermined current value, the cathode resistor of the series regulator tube and the diode, in a state of conduction, provide means to fix the cathode of the series regulator tube to substantially the voltage of the source of fixed voltage. For load currents in excess of the predetermined load current value, current through the cathode resistor of the series regulator tube increases to a point where conduction through the diode ceases. Under the latter conditions the grid of the series regulator triode tube approaches a voltage substantially equal to the voltage of the fixed voltage source, and the voltage of the cathode of the series regulator tube tends to increase, thereby serving to limit the power supply output current. With this arrangement the output voltage of the power supply is sharply decreased when the load draws current beyond a predetermined amount so that there is less danger of injuring personnel, and also less danger of damaging current-sensitive equipment. With this arrangement, also, the current through the series regulator triode tube is self limiting under excessive load current demands so that the series regulator triode tube is protected against overheating, as may ordinarily be caused by an accidental short circuit.

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 in which:

Figure l is a schematic diagram of an improved regulated power supply in accordance with the present invention; and

Figure 2 is a graph used to explain the operation of the power supply of Figure 1.

Referring now particularly to Figure 1, there is shown a regulated power supply, in accordance with the present invention, having a pair of positive and

negative input terminals

10 and 12, respectively, for applying a source of unregulated unidirectional voltage (not shown) thereacross. A variable impedance series regulator tube, such as a triode 14, has its anode connected to the positive input terminal 10 and its cathode connected to a source of fixed potential, such as ground, through a cathode resistor 18. In the illustrative arrangement, a positive output terminal 16 is also shown as being connected to ground. The negative input terminal 12 is connected to a negative output voltage terminal 20. A load, represented herein as a resistor 22, is connected across the positive and negative output terminals 16 and 20 of the power supply. It will now be understood that current from the source of unregulated voltage (not shown), which may comprise a conventional rectifier and filter unit, will flow from the economical to manufacture and yet highly eflicient in use.

positive input terminal 10, through the series regulator tube 14, the cathode resistor 18, the positive output terminal 16, the load 22, the negative output terminal 20, and back to the negative input terminal 12.

Means are provided to maintain the cathode of the series regulator tube 14 at a substantially constant voltage when the load 22 is drawing less than a predetermined amount of current. To this end, a source of fixed D.-C. voltage, represented herein as a battery 24, for example, has its negative terminal connected to the positive output terminal 16 and its positive terminal connected to the anode of a diode 26. The cathode of the diode 26 is connected directly to the cathode of the series regulator tube 14. It will now be understood that when the diode 26 is conducting the voltage at the cathode of the series regulator tube 14, with respect to ground, is substantially the voltage of the fixed voltage source 24.

Means are provided to vary the impedance of the series regulator tube 14 in response to changes in voltage across the load 22. To this end, a voltage divider 28 is connected between the positive terminal of a reference voltage source 40 and the negative output terminal 20. The voltage source 40 may be a battery or any other suitable source of D.-C. voltage. The voltage divider 28 comprises a resistor 30 connected in series with a resistor 32. An amplifier 34 has its input connected to the junction of the resistors 30 and 32 and its output connected to the control grid of an amplifier tube 36. The amplifier 34, in addition to functioning as an amplifier, also functions as a phase inverter in a manner well known in the art. The cathode of the amplifier 36 is connected to ground, and the anode thereof is connected to the anode of "the diode 26 through a load resistor 38. The anode of the amplifier 36 is also connected to the control grid of the series regulator tube 14.

The operation of the regulated power supply, in accordance with principles of the present invention, will now be described. Let it be assumed that the resistor 22 represents a Graphechon tube whose rated load current is, for example, 1 ma. Let it also be assumed that currents in excess of 1.4 ma. may damage the Graphechon tube. Under normal operating conditions, current from the source of unregulated voltage (not shown) connected across the input terminals and 12 will flow through the series regulator tube 14, the cathode resistor 18, the positive output terminal 16, the load 22, the negative output terminal 20, and back to the source of unregulated voltage through the negative input terminal 12. Let it be assumed that for one reason or another there is a tendency for the voltage across the load 22 to increase. This will result in the voltage at the negative output terminal 20 going more negative with respect to ground. Consequently, a negative-going voltage is sensed by the input to the amplifier 34, and a positive-going signal is derived from the output of the amplifier 34. This latter positivegoing voltage is applied to the grid of the amplifier 36, and a negative-going voltage is derived at the anode thereof and applied to the grid of the series regulator tube 14. A negative-going voltage on the grid of the series regulator tube 14 increases the impedance of the tube 14, and thereby decreases the current therethrough, and through the load. Thus, any tendency for the voltage across the load 22 to increase is offset by a decrease of current through the load 22 whereby the voltage across the load 22 tends to remain substantially constant. Conversely, a tendency for the voltage across the load 22 to decrease gives rise to a reverse set of conditions whereby current through the load 22 increases to stabilize the voltage thereacross.

Under normal operating conditions of the power supply thediode 26 is conducting and the voltage at the cathode of the series regulator tube 14 is substantially at the fixed voltage of the positive terminal of the fixed voltage source 24. Thus, under normal conditions of operation of the power supply, the feedback means comprising the voltage divider 28 and the amplifiers 34 and 36 serve to feed back a sample of the output voltage to the grid of the series regulator tube 14. The sample voltage is compared with the fixed voltage of the cathode of the tube 14 in order to vary "the impedance of the tube 14.

Let it now be assumed that because of a short circuit, or for some other reason, the impedance of the.load 22 is decreased so that it would ordinarily tend to draw an excessive amount of current. Under these conditions of excessive current flow, the voltage across the cathode resistor 18 increases so that the cathode of the series regulator tube 14 is at a higher potential, with respect to ground, than is the positive terminal of the fixed voltage source 24. The diode 26 will now cease conducting. The voltage at the negative output terminal 20 will tend to go positive with respect to its normal value. This positivegoing voltage is sensed by the input to the amplifier 34 and a negative-going voltage at its output is applied to the grid of the amplifier 36. This latter negative-going voltage produces a positive-going voltage at the anode of the amplifier 36 and at the control grid of the series regulator tube 14. It will be noted that, regardless of the amount of current that may be drawn by the load 22 the control grid of the series regulator tube 14 cannot go more positive than the voltage at the positive terminal of the source of fixed potential 24. Under excessive current drains, however, the diode 26 ceases to conduct and the voltage at the cathode of the series regulator tube 14 increases, thereby tending to limit the current through the series regulator tube 14. In this manner, the impedance of the series regulator tube 14 increases when the load 22 tends to draw current beyond a predetermined amount. Damage to the apparatus represented by the load 22 by excessive current, therefore, is prevented. Danger to personnel is also minimized because the voltage across the output terminals 16 and 20 tend to fall very rapidly with current drains beyond a predetermined amount. It is also possible to limit the current through the series regulator tube 14 .to the extent where even a direct short circuit across the output terminals 16 and 20 will not cause any serious damage to the regulator circuit including the series regulator tube 14.

Referring now to Figure Zthere is shown a graph representing the operating characteristics of a power supply embodying features of this invention, wherein the abscissa represents load current in ma. and the ordinate represents output voltage of the power supply in kv. When a Graphechon tube, for example, is the load on the power supply which requires a voltage of 9 kv. at a current of 1 ma., the power supply may easily provide this output power. If, for example, the apparatus represented by the load may be damaged by current in excess of 1.4 ma.,gthe diode 26, in Figure 1, may be made to cease conducting when the current drain is about 1.2 ma. This may be accomplished by a proper choice of the cathode resistor 18. When the diode 26 ceases conducting the output voltage tends to fall very rapidly with increased current demands of the load. Thus, from the output voltage-load current curve in Figure 2, it is seen that the output voltage of the power supply is substantially constant up to :a predetermined value of, say, 1.2 ma. current drain, andthen decreases sharply to substantially zero as the current drain increases to 1.4 ma.

Since it is possible to damage current-sensitive equipment like a Graphechon storage tube, as by burning its target with excessive beam current, it is seen that the regulated power supply of the present invention provides excellent means for supplying the necessary output power for a predetermined load. The power supply-of thepresent invention also provides effective means for sharply decreasing the output power when the load current is in excessof a desired amount.

The extension of the horizontal portion of the output voltage-load current curve in Figure 2, shown by the dashed line 40, represents the usual gradual drop in voltage with increased loads in typical prior art regulated power supplies.

A typical regulated power supply of the type shown and described in Figure 1, and having the outputvoltagcd cu ent Characteristics shown by the continuous curve of Figure 2, has components whose values are 'substan tially as follows:

Component: Value 14"; type 6BD4A tube. 5 18 120 K. ohms. 24 150 volts. 1.1 megohms. 32 35 megohms. 36 type 6CL6 tube. 10 38 l K. ohmsv 40 280 volts.

These values are given by way of example, and are by no means to be interpreted in a limiting sense.

Thus, there is shown and described herein, in accordance with the objects of the present invention, a regulated power supply adapted to provide a substantially constant output voltage for a rated load, and to provide for a sharp decrease in output voltage for loads in excess of a predetermined safe value. Thus, there is provided a regulated power supply that will protect current-sensitive equipment from damage by excessive current, and also protect personnel from dangerous shock while working with this equipment. The current through the series regulator tube in the control circuit of the power supply is selflimiting and may be made to flow continuously without serious damage to the series regulator tube even when the load on the power supply is a complete short circuit.

What is claimed is:

1. In a power supply of the type wherein a variable impedance multi-electrode series regulator tube is connected in series with one of a pair of output terminals of a source of unregulated D.-C. voltage and one of a pair of output terminals of said power supply, and wherein feedback means is connected to one of said electrodes to vary the impedance of said series regulator tube to compensate substantially for changes in voltage across a load connected between said pair of output terminals of said power supply, the combination therewith of means including said feedback means to maintain a second of said electrodes of said regulator tube at a substantially constant voltage while the voltage of said one of said electrodes varies when current through said load is less than a predetermined amount, and means to maintain said one of said electrodes substantially at a constant voltage while the voltage of said second of said electrodes varies when the current through said load is in excess of said predetermined amount.

2. In a power supply of the type wherein a variable impedance series regulator tube having a cathode, a grid and an anode is connected in series with a source of unregulated unidirectional voltage and a positive output terminal of the power supply, and wherein feedback means are provided to sample the power supply output voltage to a load connected between said positive output terminal and a negative output terminal and to feed back a sample of said output voltage to the grid of said series regulator tube to vary its impedance in response to voltage changes across said load, the combination therewith of a resistor connected between said cathode and said positive output terminal, a source of fixed D.-C. voltage,

a rectifier, and means connecting said rectifier and said last-mentioned source in a series circuit between said cathode and said positive output terminal.

3. In a power supply of the type wherein a variable impedance series regulator tube having a cathode, a grid and an anode is connected in series with a source of unregulated unidirectional voltage and a positive output terminal of the power supply, and wherein feedback means are provided to sample the power supply output voltage to a load connected between said positive output terminal and a negative output terminal and to feed back a sample of said output voltage to the grid of said series regulator tube to vary its impedance in response to voltage changes across said load, the combination therewith of a resistor connected between said cathode and said positive output terminal, a source of fixed D.-C. voltage, a rectifier, means connecting said rectifier and said lastmentioned source in a series circuit between said cathode and said positive output terminal, and said rectifier having a cathode connected to the cathode of said series regulator tube and an anode connected to the positive terminal of said source of fixed D.-C. voltage.

4. In a power supply of the type wherein a variable impedance series regulator tube having a cathode, a grid and an anode is connected in series with a source of unregulated D.-C. voltage and one of a pair of output terminals of the power supply, and wherein feedback means are provided to sample the output voltage to a load connected between said pair of Output terminals and to feed back a sample of said output voltage to said grid, the combination therewith of a rectifier, a source of fixed D.-C. voltage, said rectifier having a cathode connected to said cathode of said regulator tube and an anode connected to the positive terminal of said last-mentioned source, the negative terminal of said last-mentioned source being connected to one of said output terminals, and means to render said rectifier conductive when the current to said load is less than a predetermined amount and to render said rectifier nonconductive when the current to said load is greater than said predetermined amount.

5. In a power supply of the type wherein a variable impedance series regulator tube having a cathode, a grid and an anode is connected in series with a source of unregulated D.-C. voltage and one of a pair of output terminals of the power supply, and wherein feedback means are provided to sample the output voltage to a load connected between said pair of output terminals and to feed back a sample of said output voltage to said grid, the combination therewith of a rectifier, a source of fixed D.-C. voltage, said rectifier having a cathode connected to said cathode of said regulator tube and an anode connected to the positive terminal of said last-mentioned source, the negative terminal of said lastmentioned source being connected to one of said output terminals, and means to render said rectifier conductive when the current to said load is less than a predetermined amount and to render said rectifier nonconductive when the current to said load is greater than said predetermined amount, said last-mentioned means comprising a resistor connected between said cathode of said regulator tube and said one of said output terminals.

6. In a power supply of the type comprising positive and negative input terminals for applying a source of unidirectional unregulated voltage thereto, and positive and negative output terminals for connecting a load thereacross, a series tube having an anode, a grid and a cathode, and said anode being connected to said positive input terminal, the combination therewith of a resistor connected between said cathode and said positive output terminal, a diode, a source of fixed D.-C. voltage, means connecting said diode and said source of fixed D.-C. voltage in series with each other and between said cathode and said positive output terminal, means connecting said negative input and output terminals together, means to sample the voltage across said load, and means to feed back said sampled voltage to said grid.

7. A power supply comprising positive and negative input terminals for applying a source of unregulated D.-C. voltage thereacross, positive and negative output terminals for applying a load thereacross, a series regulator tube, a resistor, means connecting said tube and said resistor in series with each other and with said positive input terminal and said positive output terminal, a diode, a source of fixed D.-C. voltage, means connecting said diode and said last-mentioned source in series with each other and with said tube and said positive output terminal, means connecting said negative input and output terminals together, a voltage divider, means connecting said-voltage divider between said negative and positive output terminals, amplifying means, and means connecting said amplifying means between said tube and a point on said voltage divider.

References Cited in the file .of this patent