US 3539870 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
5. SCHNEIDER ETAL VACUUM TUBE ISOLATOR, CIRCUIT PROTECTOR, AND VOLTAGE REGULATOR Filed Jan. 15, 1969 A E a 10A 108 PowER 4 40B SUPPLY ENERGY L ENERGY STORAGE STORAGE 30A- ,308
ENERGY ENERGY ENERGY DIVERTER DIVERTER STORAGE FIG. 1 (PRIOR ART) 6O\ 6 POWER -L FUSE CIRCUIT BREAKER 4O SUPPLY I 42 3o ENERGY 22 20 L 243 FIG. 2 (PRIOR ART) so clRculT BREAKER POWER SUPPLY CONTROL CIRCUIT ENERGY STORAGE 30 ENERGY DIVERTER RF TUBE i'ad X If -61 AGENT AT TORNE Y8 United States Patent 3,539,870 VACUUM TUBE ISOLATOR, CIRCUIT PROTEC- TOR, AND VOLTAGE REGULATOR Sol Schneider, Little Silver, and George W. Taylor, Brielle, N.J., assignors to the United States of America as represented by the Secretary of the Army Filed Jan. 15, 1969, Ser. No. 791,459 Int. Cl. H02h 7/20 US. Cl. 317-51 4 Claims ABSTRACT OF THE DISCLOSURE This disclosure relates to energy control and particularly to energy control in the form of isolation and protection for multiple, amplifier circuits operating from a common power source. More particularly, this disclosure is of the use of vacuum tubes as switches for isolating and protecting individual pulse-amplifier circuits or units of a multiple-unit system having a common power supply. This disclosure teaches the connection of a vacuum tube to each of the circuits to switch it off when the circuit faults or short circuits and to switch the circuit back on when the fault clears itself. This avoids draining the main capacitor bank through the short-circuit, which could damage the individual circuit and interfere with the operation of other circuits using the same, common, power supply. The system also provides regulation of voltage to the individual circuits to increase their efficiency.
The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.
BACKGROUND OF THE INVENTION This circuit isolator was invented to meet the problems of power supplies for super power systems with pulse amplifiers for microwave pulse transmission. These systems, as the name implies, involve units of comparatively large size that handle voltages and currents, during a pulse transmission, that are considerably in excess of those encountered in conventional transmitters. The problems in super power pulse transmission systems are predictable. The voltages and currents involved are of values that approach the limits of conventional electronic circuitry. The RF tubes, themselves, are operating under conditions that make faulting or failure of the tube an unavoidable possibility. Then, too, the power surges that accompany such faulting are of a magnitude that can completely destroy the RF tube or other elements in the circuit involved, particularly when the power supply includes a large capacitor bank for energy storage.
This circuit isolator is particularly needed in systems where a plurality of pulse transmitters are required and are supplied by a single power supply. Such a situation occurs with a phased-array radar which has an extremely large antenna with many radiating elements, each powered by a separate pulse transmitter. The transmitters may all be fired together or may be fired in any sequence or phase necessary to have the desired effect on the transmitted beam. The problem is to provide protection for the individual pulse transmitters against short circuits and to minimize the damage attended on a fault in any one of the separate transmitters and, in any case, to keep the other transmitters operating with as little disturbance as possible during a fault of one of the units.
One solution would be to provide a separate power supply for each of the pulse transmitters. This would solve the problem of isolation but would be prohibitively expensive because of the cost and size of the separate power supplies. This would also be ineflicient and would not reduce the possibility of damage to any one of the units. It is more desirable and more efficient to have a single, common, power supply serving all of the pulse transmitter units. This power supply would include a main energy storage device in the form of a capacitor bank of suflicient capacity to supply the instantaneous power requirement of the entire system. Additional energy storage banks are also connected to each, individual pulse transmitter to provide the instantaneous energy needed during pulse transmissions at the actual location of the pulse transmitter to prevent jitter and electronic beam path instability due to the length of the lines between the main energy storage bank and the individual pulse transmitters.
When the systems are operating from a common power supply, each of the pulse transmitters is connected to the common power supply through an isolator. Isolators are usually used with each individual circuit to stop the discharge of the main capacitor bank until the secondary capacitor bank is discharged and the fault is cleared.
The isolator can take various forms, the most common form having passive components which may be merely a high voltage fuse with a backup circuit breaker. In the event of a fault the fuse would blow and the circuit breaker would open. The discharge current in the fuse would be quenched by sand or other medium in a well known manner.
The passive component isolator has the serious disad- 'vantage of inactivating the circuit until the fuse is replaced and is tolerable only if faulting rarely occurs or if the system can operate effectively without some of the pulse transmitters. There is also a question as to whether the fuse could open quickly enough to avoid a surge of current that might be enough to destroy the pulse transmitter or to effect the stability of the common power supply.
A vacuum tube type of switch connected in series with each of the pulse transmitters would be one way of interrupting the flow of current from the main capacitor bank and isolating the individual transmitters. In the event of a fault the vacuum tube could be switched off, thereby interrupting energy flow and providing protection for the pulse transmitter. After the fault clears, the vacuum tube could be automatically switched on again.
However, such a vacuum tube would have to be specially designed to operate under the extremely high changes of voltage with respect to time that would result from the transients that occur when the load faults. For example, changes in voltage with respect to time in the order of 300,000 volts per microsecond could appear across such an interrupter in existing pulse transmitters and, in all likelihood, a conventional triode or tetrode would are under these conditions. The tube must also have, for maximum efliciency, a low voltage drop, which again, is not found in standard equipment.
Such a tube would also require low input capacitance and low drive voltage since if the storage capacitance across the RF tube of the pulse transmitter is removed, the vacuum tube interrupter switch must be driven to full conduction of current in a fraction of a microsecond. Typical equivalent input capacity of vacuum switch tubes is in the order of 1 to 4 picofarads per ampere of plate current. The grid voltage swing is in the order of 2 to 4 kilovolts for a beam current of amperes and the turn on time of /2 microsecond. A grid drive peak current in excess of 400 amperes would be required for the best available tubes, There are no tubes presently available that can meet all these requirements.
It is therefore an object of this invention to provide an interrupter switch for an RF pulse transmitter that can use a conventional vacuum tube.
It is a further object of this invention to provide a vacuum-tube current interrupter switch and voltage regulator that can isolate a circuit from the main power supply in the event of a fault in that circuit to minimize the damage to the circuit during such a fault.
SUMMARY OF THE INVENTION The isolation of a pulse transmitter from a common power supply, and the regulation of the voltage and current to the RF amplifier tube of the pulse transmitter is achieved by connecting a high-current vacuum tube between the primary, energy-storage, capacitor bank of the common power supply and the secondary energy-storage capacitor bank at the pulse transmitter. The resistive and inductive elements that are normally included are connected between the secondary capacitor bank and the RF amplifier tube of the pulse transmitter. An energy diverter with a series, limiting resistor is connected across the RF tube itself. A voltage sensing means across the RF tube actuates a control circuit for the vacuum tube isolator and regulator.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of a conventional system for connecting multiple, isolated circuits to a common power supply;
FIG. 2 shows a single unit of such a system with a fuse type isolator circuit; and
FIG. 3 shows a single unit of such a system with a vacuum tube isolator and regulator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a common power supply 6 is coupled to an energy-storage device 8 which supplies several pulse amplifier circuits such as A and B. In FIG. 1 each of the circuits has an isolator 10A, 10B, etc. separating the output loads A, 20B, etc. of the individual circuits from the common power supply. Each circuit normally has a secondary energy-storage device 40A, 40B, etc. and a diverter A, 30B, etc.
FIG. .2 shows the elements of FIG. 1 in more detail and similar elements are similarly numbered. The common power supply 6 and the energy-storage device 8 supply the load which is an RF tube 20. The secondary energy-storagedevice is a capacitor bank 40. The RF tube has a tertiary capacitive energy-storage device 24 and is connected across an energy diverter 30 through a current limiting resistor 22. The secondary capacitor bank 40 supplies current to the load 20 through the resistor 42 and the inductor 43 which are needed to reduce and control the flow of current during a fault discharge. Each of the units is isolated and protected by a fuse 60 and a circuit breaker 61.
In operation, if faulting of the RF tube 20 occurs, the energy diverter circuitry senses changes in voltage or current due to the fault, and fires itself to provide a current bypass for the faulting RF tube. This burns out the fuse and trips the circuit breaker to disconnect the common power supply from the pulse transmitter circuit. The inductance 43 delays the rise of fault current, and the resistor 42 limits the peak current and absorbs the energy drawn by the diverter 30. The resistor 22 limits the current through the RF tube itself during a fault. The fuse must be replaced, and the circuit breaker reset after the energy diverter discharges the capacitor 40 and the faulting of the RF tube clears itself.
FIG. 3 shows this invention applied to a. circuit similar to that of FIGS. 1 and .2, and similar elements are again, similarly numbered. The power supply 6 and the main, energy-storage, capacitor bank 8 supply current to the RF tube 20. Additional power is available from the secondary and tertiary capacitor banks 40 and 24 as needed. The resistors 22 and 42 have the same function as before, as does the inductance 43. A fuse 60 and circuit breaker 61 may again be provided for each unit, but
the main isolator or current interrupter is now the vacuum tube switch 10 which may also serve as a voltage regulator.
The vacuum tube switch is, effectively, connected between the common power supply 6 and the secondary capacitor bank 40'. The vacuum tube is actuated by a control circuit 1 6 which is actuated by a voltage sensor 26.
The operation of a system such as a phased-array radar is fairly well known. Such a system has a plurality of pulse transmitters including RF tubes such as 20 that are fired in a well known manner in any desired sequence or phase. Each of the RF tubes draws current from the main capacitor bank such as 8 of a common power supply with additional secondary or tertiary capacitor banks meeting the instantaneous demands for additional current that is necessary when the inductive effects of toolong power lines delays the current to the individual pulse transmitters.
In the operation of this particular isolator and regulator circuit, any faulting of the RF tube will appear as a short circuit with a sudden current surge or voltage drop which is sensed, as in the forementioned circuit operation, by the energy diverter, which fires to bypass the current away from the RF tube. However, in this circuit, the change in voltage across the RF tube is also detected by the voltage sensor 26 to actuate the control circuit 16 which cuts oif the vacuum-tube switch 10. This vacuum tube switch is connected, on one side, to the common power supply 6 whose energy storage device 8 is a capacitor bank which will vary in voltage only very slowly because of the considerable capacity involved. However, as pointed out earlier, if the RF tube of a pulse amplifier of a super-power system faults, changes of voltage with respect to time in the order of 300,000 volts per microsecond or greater can appear across any isolator and, in all likelihood, a conventional triode or tetrode switch tube, connected directly between the main capacitor bank and the RF tube, would also are under these conditions. Consequently, in this circuit, the other side of the vacuum tube switch 10' is connected directly to the secondary capacitor bank 40 rather than being connected directly to the RF tube 20. Consequently, the voltage across this vacuum tube switch can change only as fast as 40 is discharged through the inductor 43 and the resistor 42 and this prevents the high change of voltage with respect to time from appearing across the vacuum-tube switch 10'. When the energy diverter completes the discharge of capacitor bank 40 and the RF tube fault clears itself, the voltage sensor and control circuits reactivate the vacuum-tube switch.
In this circuit, the ratio of the capacity of the secondary capacitor bank 40, the inductance 43 and resistance 42 which form the energy diverting loop through the energy diverter 30 is designed to be slightly over-damped, rather than under-damped so that no voltage reversals appears across the vacuum-tube switch. Since there are not extreme voltage changes, in either direction, across the vacuum-tube switch, available in triodes and tetrodes can be used with a minimum danger of arcing.
The tube also can serve as a voltge regulator if suitable voltage sensing is incorporated in the circuit. The control circuit and input capacitance of triodes limits their response time. In a practical circuit the minimum response time will be in the order of 2 to 3 microseconds. For a chain of closed spaced narrow pulses, direct regulation for the individual pulses cannot be provided. However, by programming the control circuit, the regulator interrupter tube can be pre-pulsed to the desired operation level and since the input capacitance of the tube is fully charged, it can respond rapidly to small variations in voltage. If the control circuitry is programmed to allow the regulator tube to pass a sizeable portion of the current to the RF tube, there are the additional advantages of increase in overall efficiency and reduction in secondary capacitance requirements. These can be accomplished without any loss of voltage regulation or system reliability but require an increase in the common power supply voltage drop in the vacuum-tube switch.
The increase in overall system efiiciency is simply due to the decreased energy drained from the secondary capacitance bank. Since the secondary capacitance is resistively charged, energy equal to the amount of capacitor recharge energy is dissipated during recharge. When the vacuum tube delivers energy directly from the common power supply to the RF tube the only energy loss is caused by that portion of the power supply voltage that represents the voltage drop in the tube. The usual vacuum tube voltage drop is approximately percent of the power supply voltage.
Only one of the pulse transmitters has been shown in FIGS. 2 and 3, for simplicity. It is obvious, however, that any number of additional units, like the one shown in FIG. 1, are intended to be added as needed.
Sensor 26 is indicated as a voltage sensor in the embodiment of the invention described here, since voltage sensing is an efiective manner of actuating the control circuit. However, it should be obvious that current sensing or voltage and current sensing would be equally applicable here.
The vacuum-tube switch 10 may be of any available type that will carry the current required for normal operation of the pulse transmitters. The RF tube 20 can be similarly chosen. The values of the current limiting resistors and inductors must be chosen with respect to the currents and voltages to be accommodated.
While the need for such isolators is clearly seen in these extremely high voltages and currents of superpower amplifiers and transmitters where the faulting of a tube and short circuiting of a capacitor bank represents enormous and dangerous amounts of electrical power, this system is also applicable to smaller devices where the replacing of a fuse is inconvenient or the sudden change of the power supply voltage is undesirable.
While we have considered here the use of vacuum-tube switches in certain, very high powered systems, it is obvious that transistors of one kind and another may also be used here within their available power output and other characteristics since it is just as possible to have a fault across a transistor as a vacuum tube. Similarly, the current interrupter and regulator 10 may be a solid state device with suitable control and voltage sensing circuits or devices.
Having described my invention, what is claimed is:
1. In combination with a power supply having a first capacitor bank, and a pulse amplifier having an output tube and a second capacitor bank connected to said output tube through a resistor and an inductor, a protective circuit for coupling said pulse amplifier to said power supply comprising: a vacuum-tube switch having at least one control electrode; means for connecting said vacuum-tube switch between said first capacitor bank and said Second capacitor bank; a voltage sensitive device having an input and an output; a control circuit having an input and an output; means for connecting the input of said voltage sensitive device across said output load; means for connecting said output of said voltage sensitive device to said input of said control circuit; means for connecting the output of said control circuit to said control electrode of said vacuum-tube switch.
2. In combination with a power supply as in claim 1 a plurality of said pulse amplifiers, each having one of said protective circuits as in claim 1.
2. In a protective circuit as in claim 1, an energy diverter, and means for connecting said energy diverter across said RF tube.
4. In a protective circuit as in claim 3 said means for connecting said energy diverter across said RF tube including a current-limiting resistor.
References Cited UNITED STATES PATENTS 2,438,962 4/ 1948 Burlingame et a1. 3289 2,815,445 12/1957 Young et al. 3175l X 2,845,529 7/1958 Weldon 328-9 3,277,342 10/1966 Ross 3l75l X JAMES D. TRAMMELL, Primary Examiner U.S. Cl. X.R. 307108; 3289