US3072802A

US3072802A - Pulse driver with magnetic amplitude and width control

Info

Publication number: US3072802A
Application number: US786789A
Authority: US
Inventors: Edward F Myers; Young Edward William
Original assignee: Burroughs Corp
Current assignee: Unisys Corp
Priority date: 1959-01-14
Filing date: 1959-01-14
Publication date: 1963-01-08
Anticipated expiration: 1980-01-08

Description

Jan. 8, 1963 E. F. MYERs ETAL 3,072,802

PULSE DRIVER WITH MAGNETIC AMPLITUDE AND WIDTH CONTROL Filed Jan. 14, 1959 l4 Ib NNC '3 LOAD DEGENERATIVE Q FEEDBACK 25 REGENERATIVE g9 FEEDBACK 2 SUCCEEDING DRIVER STAGE INVENTORS EDWARD F. MYERS BY EDwARD w. YOUNG United States Patent PULSE DRIVER wrTIr MAGNETIC AMPLITUDE AND WIDTH CONTROL Edward F. Myers, Yeadon, and Edward William Young, Philadelphia, Pa., assignors to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Jan. 14, 1959, Ser. No. 786,789 5 Claims. (Cl. 30788.5)

This invention relates to pulse-forming circuits and more particularly to a novel driving circuit for providing current pulses having controlled amplitudes and widths.

A variety of circuits for supplying constant current pulses to a load are well-known in the electronics art. In order to achieve the desired current regulation, present day current drivers employ complicated circuits which waste space, are inefficient, and ultimately lessen the overall dependability of the system in which they are used.

The present invention is characterized by inherent current regulation achieved with economy of components and simplicity of design. The regulation results from the action of two pulse transformers on a current amplifying device. The degree of conduction of the current device, subsequent to the application of a trigger pulse thereto, is the resultant of the respective regenerative and degenerative effects of the pulse transformers on the current device. One of the transformers is adapted to shape the current pulse while the other controls its amplitude. If desired, a number of driver circuits may be operated in tandem by allowing the current pulse of one driver to trigger the succeeding driver. This latter technique is particularly useful in operating different elements of magnetic shift registers for matrix storage systems which require a plurality of sequential interrogation pulses. Thus, by combining two or more of the instant driver circuits, a generator is obtained which may be triggered to deliver a sequence of two or more timed current waveforms.

Although not limited thereto, a preferred embodiment of the instant invention utilizes one transistor as the drive means and a pair of pulse transformers as control means; thereby combining the inherent advantages of the solid state components with those of the circuit configuration.

Accordingly, it is a general object of the invention to provide an improved pulse-forming circuit for generating current pulses.

Another object of the invention is to provide driving circuits for delivering a sequence of current pulse waveforms.

A further object of the invention is to provide a current driver circuit having the combined advantages of simplicity, efficiency and economy.

A still further object of the invention is to provide a driver circuit which utilizes exclusively solid state electronic components.

A more specific object of the present invention is to provide a self-regulating pulse-forming circuit which makes use of the respective regenerative and degenerative effects of a pair of pulse transformers on the conduction of an amplifier device.

These and other features of the invention are apparent from the preferred embodiment described in the following, with reference to the drawing which is a schematic diagram of the current driver according to the instant invention.

Referring now to the drawing, there is shown an illus trative embodiment of the present invention comprising a PNP transistor having an emitter 11, base 12, and a collector electrode 13, a first pulse transformer 20 having a primary winding 21 and two secondary windings 3,072,802 Patented Jan. 8, 1963 2 22 and 23 respectively, and a second pulse transformer 30 having a primary winding 31 and a secondary winding 32. It should be noted that the invention is not restricted to the use of a PNP-type transistor, but may employ other types in accordance with established design procedures well known to those skilled in the art.

With respect to the transformers, the polarities of the voltages developed across the same windings coupled thereto are material to the operation of the circuit. Therefore a dot has been aflixed adjacent that end of each Winding which has the same polarity of voltages with respect to the other end thereof, as every other winding so designated, for a predetermined direction of magnetization of the transformer core.

A. trigger pulse source 50 is connected to input terminal 15. Blocking diode 14 allows only trigger pulses of the proper polarity to pass to the base electrode 12 of transistor 10. Emitter electrode 11 is connected to ground potential. Collector electrode 13 is connected to a source of negative potential E by means of a circuit comprising the load 40, primary winding 31 of transformer 30, and primary winding 21 of transformer 20. A diode 24 is connected in parallel with transformer winding 21. The base electrode 12 of transistor 10 is returned to ground potential through a circuit comprising the parallel combination of secondary winding 32 and resistor 33, and secondary winding 22. A clamping diode 25 is connected between the dotted terminal of winding 22 and the collector supply voltage E An additional secondary winding 23 is coupled to transformer 20. A capacitor 26 and resistor 27 are connected in series across the terminals of winding 23 to form a differentiating network, the output of which is available at terminal 15 to trigger a succeeding driver stage 60. I

Referring now to the operation of the circuit shown in the drawing, it will be assumed that initially transistor 10 is not conducting. The legend NNC applied to transistor It) stands for normally nonconductive. A negative trigger pulse applied to terminal 15 from source 50 passes via diode 14 to the base 12 of transistor 10. The transistor is triggered to conduction and thereafter collector and base currents I and l respectively flow in the direction of the arrows as indicated in the drawing. Collector current I flows through the load 40 and the primary impedances of

transformers

30 and 20 respectively, and then back to ground through the collector supply E Diode 24 is placed across winding 21 to prevent the oscillations, or ringing, associated with the recovery of the transformer at the termination of the current pulse. A diode is not necessary across winding 31 since oscillations are prevented by the impedance of resistor 33 reflected into the primary circuit of transformer 30. Base current I flows through the parallel impedance of resistor 33 and winding 32 of transformer 30, and then through secondary winding 22 of transformer 20 to ground as a result of the voltages induced by the flow of l hereinafter explained.

The action of transformer 20 on the overall circuit operation will now be considered as though transformer 30 were not present. Current I flowing through winding 21 induces a voltage across winding 22 of such a polarity that the dotted terminal of said latter winding is negative with respect to the undotted terminal. This negative voltage is impressed on the base electrode 12 of the transistor and maintains the conduction thereof after the trigger pulse has terminated. The duration of said conduction, or alternately stated, the width of the current pulse delivered to the load is a function of the magnitude of the collector current l the characteristics of the magnetic material of pulse transformer 20, the turns ratio of the windings on transformer 20 and the magnitude of the supply voltage E Since the voltage developed across winding 22 by current I flowing through winding 21 is clamped at the supply potential E it is assumed that the voltage across winding 22 is constant at the E level. The pulse duration At is then given approximately by the expression:

where L is the inductance of winding 22 and Ai is the value of collector current I transformed into the secondary circuit of transformer 20. The turns ratio of windings 21 and 22 is chosen such that with the minimum value of at expected during circuit operation, the pulse transformer 20 saturates. When saturation occurs the voltage across winding 22 decreases rapidly toward zero, and the transistor deprived of the negative bias on its base, ceases to conduct. Since the pulse width of the load current is dependent on the clamping level, a variable width constant current driver can be mechanized simply by clamping the voltage induced across winding 22 to a variable voltage source instead of to the fixed potential E As hereinbefore mentioned, the amplitude of the current pulse delivered to the load is controlled by transformer 30. The combination of resistor 33 and the transformer 30 may be represented by an equivalent primary resistance. Current I flowing through this primary resistance causes a voltage drop thereacross which is transformed into the secondary with a value determined by the turns ratio of transformer 30. The latter voltage appearing across winding 32 is applied to the base of transistor 10 and is of such polarity as to tend to decrease the conduction thereof. There is an additional voltage drop appearing across the parallel combination of winding 32 and resistance 33 which results from the base current I flowing therethrough. In practice, even under worst-case conditions, this voltage is small and has no appreciable effect on the regulating properties of the instant circuit. Therefore, this latter voltage is neglected in the succeeding consideration of circuit op eration.

In the preceding description of the function of transformer 20 it was noted that the conduction of the transistor, subsequent to the trigger pulse, was maintained by the voltage generated across winding 22. It should now be apparent that the actual bias appearing on the base of the transistor is the algebraic sum of the voltages appearing respectively across windings 22 and 32. Thus the eifect of transformer 20 on the conduction of the transistor is regenerative, while transformer 30 is degenerative. Obviously, if the circuit is to supply current pulses to a load, the net effect of the transformers must be regenerative. Since the voltage across winding 22 is a constant value, as determined by the supply voltage E the voltage across the secondary of transformer 30 will control the bias on the transistor and thereby the magnitude of the collector current flowing through the load 40. If the variation in the load impedance results in a tendency for I to increase or decrease from a design value, this tendency is sensed by the transformer 30 and is reflected as a change in the voltage across winding 32. This change in secondary voltage results in a change of the net bias on the transistor of such an instantaneous polarity to cause the collector current 1 to remain at its design value.

It will be assumed that it is desired to have a design value of current flowing through the load 40[ Since the load current is the collector current I of the transistor, the bias which must be applied to'the transistor to obtain the design load current is easily ascertained from the transistor characteristic curves which relate collector current to base-emitter bias. As hereinbefore explained, the voltage appearing across winding 22 is equal to the supply voltage E Resistor 33 is selected such that the algebraic sum of the voltage appearing across the secondary circuit of transformer 30 and the supply voltage E is the value of bias voltage required to produce the design load current. If the load impedance is diminished, current I will tend to rise above the desired level. This increase in load current results in a larger voltage across the equivalent primary resistance of transformer 30 and a proportional increase in the secondary voltage across winding 32 in accordance with the turns'ratio. This increase in the secondary voltage of transformer 30 causes a less negative bias to appear on the transistor 10, and the collector current I is adjusted to its design value. Conversely, if I tends to decrease from the design value, the voltage across the secondary circuit of transformer 30 will decrease and the bias on the transistor will become more negative, thereby increasing the conduction of the transistor and causing I to return to its design value.

An important characteristic of the design of the instant driver circuit is that transistors having different values of ,3 (the ratio of collector current to base current) may be substituted for one another in the circuit without appreciably alfecting its overall operation. The only consideration which must be made is that of providing suflicient base current for a minimum 5: transistor throughout the range of instantaneous load currents which may be encountered during circuit operation.

As mentioned previously, the present driver circuits are amenable to tandem operation. The voltage pulse induced across winding 23 of transformer 20 by load current flowing through winding 21 is differentiated by capacitor 26 and resistor 27. The trigger-type voltages associated respectively with the leading and trailing edge of the differentiated pulse appear at terminal 15'. These voltages are applied to a succeeding driver stage 60 which selects a trigger voltage of the proper polarity to initiate the succeeding current pulse cycle.

From the foregoing description of the invention it is evident that the present technique of utilizing the respective regenerative and degenerative effects of a pair f pulse transformers on a current amplifying device results in efficient and dependable current regulation. It must be understood that while a preferred embodiment of the invention has been shown, this embodiment is meant to be illustrative only, and is not limitative of the invention. For example, a vacuum tube may be substituted for the transistor; or the pulse transformers may be replaced with magnetic cores having substantially rectangular hysteresis characteristics. Many additional modifications will be suggested to those skilled in the art, and all such variations as are in accord with the principles discussed previously are meant to fall within the scope of the appended claims.

What is claimed is:

l. A circuit for delivering a regulated current pulse to a load comprising a current amplifying device, the degree of conduction of said device being a function of the voltage applied thereto, first and second transformers connected in a series path with said load and said current amplifying device, said load current flowing in said series path, said first transformer generating a constant voltage in response to the flow of said load current, said constant voltage when applied to said amplifying device being regenerative with respect to the conduction thereof, said second transformer generating a voltage having a magnitude proportional to the amplitude of said load current, said latter voltage when applied to said amplifying device being degenerative with respect to the conduction thereof, means for applying the voltages generated by said first and second transformers concurrently to said amplifying device, said generated voltages producing a resultant voltage for controlling the conduction of said device and the corresponding amplitude of load current, said resultant voltage having a polarity to sustain the conduction of said amplifying device throughout the period of nonsaturation of said first transformer, variations in said load current during said nonsaturated period resulting in an instantaneous change in said resultant voltage of such magnitude as to maintain the amplitude of said load current substantially constant, the saturation of said first transformer by said load current resulting in the termination of said regenerative voltage whereby the resultant voltage applied to said amplifying device is of a polarity to terminate the flow of load current.

2. A circuit for generating pulses of regulated load current comprising a current amplifying device having at least an input electrode and an output electrode, said amplifying device being adapted to supply current to a load coupled to said output electrode, the amplitude of said load current being a function of the voltage applied to said input electrode of said device, first and second transformers, a primary winding and a secondary winding coupled to each of said transformers, said primary windings being connected in series to said output electrode and said load, said secondary windings being connected in series to said input electrode, impedance means connected in parallel with said secondary winding of said second transformer, means for applying a trigger pulse to said input electrode for initiating the flow of load current from said amplifying device, said load current flowing through said primary windings inducing a voltage across each of said secondary windings, means for clamping the voltage induced across the secondary of said first transformer to a fixed potential, said latter induced voltage having a polarity which when applied to said input electrode is regenerative with respect to the flow of said load current, the secondary voltage of said second transformer having a magnitude proportional to the amplitude of said load current and a polarity which when applied to said input electrode is degenerative with respect to the flow of said load current, said secondary voltages producing a resultant voltage on said input electrode of said amplifying device, said resultant voltage determining the degree of conduction of said device and the corresponding amplitude of load current, said resultant voltage having a polarity to sustain the conduction of said amplifying device throughout the period of nonsaturation of said first transformer, variations in said load current during said period resulting in an instantaneous change in said resultant voltage of such magnitude as to maintain the amplitude of said load current substantially constant, the saturation of said first transformer by said load current resulting in the termination of said regenerative voltage whereby the resultant voltage applied to said amplifying device is then of such polarity as to preclude the continued conduction of said device and the fiow of load current.

3. A pulse forming circuit as defined in claim 2 Wherein said clamping means comprise a diode having one of its electrodes coupled to a source of clamping potential and the other of its electrodes coupled to one end of said secondary winding on said first transformer in such a manner that the voltage induced across said latter secondary winding cannot exceed the level of said clamping potential.

4. An electronic circuit for supplying load current pulses having controlled amplitudes and pulse widths comprising a transistor having an emitter, collector and base electrode, said transistor being adapted to supply current to a load coupled to said collector electrode, the amplitude of said load current being a function of the bias voltage applied between said emitter and base electrodes, said emitter electrode being connected to a reference potential, first and second pulse transformers, a primary winding and a secondary winding coupled to each of said transformers, said primary windings being connected in series with said collector electrode and said load, said secondary windings being connected in series with said base electrode, impedance means connected in pareach of said secondary windings, diode means for clamping the voltage induced across the secondary of said first transformer to a fixed potential, said latter induced voltage having a polarity which when applied to said base electrode is regenerative with respect to the flow of current from said transistor, the secondary voltage of said second transformer having a magnitude proportional to the amplitude of said load current and a polarity which when applied to said base electrode is degenerative with respect to the flow of said load current, said secondary voltages providing a resultant bias voltage on the base of said transistor, said bias determining the degree of conduction of said transistor and the corresponding amplitude of load current, the polarity of said bias voltage being suitable for sustaining the conduction of said transistor throughout the period of nonsaturation of said first transformer, variations in said load current during said nonsaturated period resulting in an instantaneous change in said bias voltage of such magnitude as to maintain the amplitude of said load current substantially constant, the saturation of said first transformer by said load current resulting in the termination of said regenerative voltage, whereby the bias applied to said transistor is then of such polarity as to preclude the continued conduction thereof.

5. A driver circuit for supplying a sequence of regulated current pulses to a load comprising a PNP junctiontype transistor having an emitter, collector and base electrode, said transistor being adapted to supply current to a load connected to said collector electrode, the amplitude of said load current being a function of the bias voltage applied between said emitter and base electrodes, said emitter electrode being connected to ground potential, first and second pulse transformers, a primary winding and first and second secondary windings coupled to said first transformer, a primary winding and a secondary winding coupled to said second transformer, said primary windings being connected in series with said collector electrode and said load, said first secondary winding of said first transformer and the secondary winding of said second transformer being connected in series'with said base electrode, a resistive element connected in parallel with said first secondary winding of said first transformer, means coupled to said base electrode for applying a short duration negative trigger pulse thereto for initiating the conduction of said transistor, the flow of said load current through said primary windings inducing a voltage across each of said secondary windings, diode means for clamping the voltage induced across said first secondary winding of said first transformer to a fixed potential, said latter induced voltage having a negative polarity which when applied to the base electrode of said transistor is regenerative with respect to the flow of load current, the secondary voltage of said second transformer having a magnitude proportional to the amplitude of said load current and a positive polarity which when applied to the base electrode of said transistor is degenerative with respect to the flow of said load current, the algebraic sum of said regenerative and degenerative voltages appearing as a bias voltage on the base of said transistor, said bias determining the degree of conduction of said transistor and the corresponding amplitude of load current, the neg ative polarity of said bias voltage tending to sustain the conduction of said transistor throughout the period of nonsaturation of said first transformer, variations in said load current during said nonsaturated period resulting in an instantaneous change in said bias voltage of suchmagnitude as to maintain the amplitude of said load current substantially constant, the saturation of said first transformer by said load current resulting in the termination of said regenerative voltage, whereby said bias is then of positive polarity which precludes the further conduction of said transistor, means for difierentiating the voltage pulse induced across said second secondary winding of said first transformer, the differentiated output pulse'which occurs in phase with the cessation of conduction of said transistor being suitable for triggering a succeeding driver circuit.

References Cited in the file of this patent UNITED STATES PATENTS Bennett Mar. 6, 1951 Hepp Jan. 15, 1952 Light Sept. 30, 1958 Rogers May 12, 1959 Finkelstein et -al Feb. 23, 1960 FOREIGN PATENTS Great Britain Dec. 2, 1953

Claims

1. A CIRCUIT FOR DELIVERING A REGULATED CURRENT PULSE TO A LOAD COMPRISING A CURRENT AMPLIFYING DEVICE, THE DEGREE OF CONDUCTION OF SAID DEVICE BEING A FUNCTION OF THE VOLTAGE APPLIED THERETO, FIRST AND SECOND TRANSFORMERS CONNECTED IN A SERIES PATH WITH SAID LOAD AND SAID CURRENT AMPLIFYING DEVICE, SAID LOAD CURRENT FLOWING IN SAID SERIES PATH, SAID FIRST TRANSFORMER GENERATING A CONSTANT VOLTAGE IN RESPONSE TO THE FLOW OF SAID LOAD CURRENT, SAID CONSTANT VOLTAGE WHEN APPLIED TO SAID AMPLIFYING DEVICE BEING REGENERATIVE WITH RESPECT TO THE CONDUCTION THEREOF, SAID SECOND TRANSFORMER GENERATING A VOLTAGE HAVING A MAGNITUDE PROPORTIONAL TO THE AMPLITUDE OF SAID LOAD CURRENT, SAID LATTER VOLTAGE WHEN APPLIED TO SAID AMPLIFYING DEVICE BEING DEGENERATIVE WITH RESPECT TO THE CONDUCTION THEREOF, MEANS FOR APPLYING THE VOLTAGES GENERATED BY SAID FIRST AND SECOND TRANSFORMERS CONCURRENTLY TO SAID AMPLIFYING DEVICE, SAID GENERATED VOLTAGES PRODUCING A RESULTANT VOLTAGE FOR CONTROLLING THE CONDUCTION OF SAID DEVICE AND THE CORRESPONDING AMPLITUDE OF LOAD CURRENT, SAID RESULTANT VOLTAGE HAVING A POLARITY TO SUSTAIN THE CONDUCTION OF SAID AMPLIFYING DEVICE THROUGHOUT THE PERIOD OF NONSATURATION OF SAID FIRST TRANSFORMER, VARIATIONS IN SAID LOAD CURRENT DURING SAID NONSATURATED PERIOD RESULTING IN AN INSTANTANEOUS CHANGE IN SAID RESULTANT VOLTAGE OF SUCH MAGNITUDE AS TO MAINTAIN THE AMPLITUDE OF SAID LOAD CURRENT SUBSTANTIALLY CONSTANT, THE SATURATION OF SAID FIRST TRANSFORMER BY SAID LOAD CURRENT RESULTING IN THE TERMINATION OF SAID REGENERATIVE VOLTAGE WHEREBY THE RESULTANT VOLTAGE APPLIED TO SAID AMPLIFYING DEVICE IS OF A POLARITY TO TERMINATE THE FLOW OF LOAD CURRENT.