US3239681A

US3239681A - Current driver circuit

Info

Publication number: US3239681A
Application number: US121412A
Authority: US
Inventors: Milton F Bond
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1961-07-03
Filing date: 1961-07-03
Publication date: 1966-03-08
Anticipated expiration: 1983-03-08

Description

March 8, 1966 F, BOND CURRENT DRIVER CIRCUIT Filed July 5, 1961 76 lllll 72 BI 55 82 83 H FIG. 2 F

66 "0" I26 I22 IIO +v2 2 BN4 m FIG. 3

I54 I43 I45 I34 '76 I44 I46 INVENTOR MILTON F. BOND ATTORNEY United States Patent 3,239,681 CURRENT DRIVER CIRCUIT Milton F. Bond, Apalachin, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed July 3, 1961, Ser. No. 121,412 3 Claims. (Cl. 307-88) This invention relates generally to current driver circuits and more particularly to a constant current pulse driver circuit for driving a variable impedance load.

A current driver circuit provides current for an impedance load. For a variable impedance load, it has heretofore been diflicult to maintain an appropriate current level over the entire range of the impedance variation. In certain applications of magnetic cores, with substantially rectangular hysteresis loops, a plurality of the cores are in random remanence states. Since in these applications both the magnitude of the initial magnetic core load and time variation of the impedance thereof during switching are often random, it has been difiicult to provide a constant current pulse driver which would maintain the required constant current level in the case load during the switching of the cores thereof.

It is an object of this invention to provide a current driver circuit for an impedance load.

It is another object of this invention to provide a constant current driver circuit for a variable impedance load.

It is still another object of this invention to provide a constant current pulse driver circuit for a variable impedance load over the entire range of the impedance variation.

It is a further object of this invention to provide a constant current pulse driver circuit for a magnetic core load with unpredictable initial impedance and time variation thereof.

It is still a further object of this invention to provide a constant current pulse driver circuit for a magnetic core load which has a current pulse time duration required to switch every magnetic core therein.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustratted in the accompanying drawings.

In the drawings:

FIGURE 1 illustrates a first preferred embodiment of this invention having a feedback network connected between the emitter and base of a driver transistor which utilizes a control magnetic core and a Zener diode to assure a constant voltage pulse feedback during switching of the magnetic core load.

FIGURE 2 illustrates the substantially rectangular hysteresis loop for the magnetic cores described for this invention.

FIGURE 3 illustrates a second preferred embodiment of this invention which differs from the embodiment thereof shown in FIG. 1 in that the feedback network includes, instead of the Zener diode, an RC network to provide shaping for the feedback voltage pulse and a series resistor-diode path for controlling the switching time of the control magnetic core.

This invention provides a constant current pulse driver circuit for a variable impedance load whose initial impedance and impedance time variation are random. It includes a current conductable switching device with current conduction control means therefor. The control means has a feedback circuit to assure that the application of a trigger signal to the constant current pulse driver circuit causes constant current conduction through the variable impedance load during the time variation of its impedance. The feedback circuit has a voltage pulse 3,239,681 Patented Mar. 8, 1966 feedback magnitude limiting means and a net ampereturns limiting means to assure that the action of the feedback circuit overlaps the time variation of the load impedance.

A feature of this invention involves a constant current pulse driver circuit for resetting a magnetic core load having a plurality of magnetic cores with substantially rectangular hysteresis-loop characteristics. The collectoremitter current of a driver transistor in the circuit is maintained constant by a feedback network which maintains constant the voltage across the base to emitter junction of the transistor during the switching of the core load. The control winding of a control magnetic core with a substantially rectangular hysteresis-loop characteristic is connected in series in the collector-emitter path. The collector-emitter current flows through the control winding and the windings of the magnetic cores to be switched. A feedback winding on the control core is connected between the emitter and base electrodes of the driver transistor. Application of a positive going input trigger signal to the base of the driver transistor turns it 0N so that collector-emitter current flows to the magnetic core load. A voltage is induced from the control winding on the control magnetic core to the feedback winding thereon by transformer action which maintains a forward bias on the base of the driver transistor. Therefore, the driver transistor remains ON after the input trigger signal applied thereto has terminated. The driver transistor turns OFF when the control magnetic core saturates. Saturation of the control magnetic core occurs because of its hysteresis-loop characteristic. When the control core saturates, the voltage across the feedback winding terminates and removes the forward bias on the base-emitter junction of the driver transistor.

A constant current pulse driver circuit in accordance with this invention has considerable utility, illustratively, for set and reset of the magnetic cores of magnetic core logic and memory circuits.

With reference to FIG. 1, the structure of a constant current pulse driver 10, in accordance with this invention, for resetting a magnetic core load 12 will be described. The current driver 10 includes an NPN driver transistor 14 having collector 16, base 18 and emitter 20. In practice, through conventional technique driver 10 can readily be adapted to incorporate a PNP driver transistor instead of the NPN driver transistor 14. The collector 16 is connected to positive voltage source +V at terminal 22 via a resistor 24. Base 18 is connected toinput trigger signal terminal 26 via diode 28 whose anode 30 is connected to input trigger signal terminal 26 and whose cathode 32 is connected to base 18. The emitter 20 is connected in series with control winding 34 on control magnetic core 36. Control winding 34 passes through magnetic core load 12 in magnetic coupling relationship therewith by winding 37 to ground 38. Magnetic core load 12 comprises, illustratively,

magnetic cores

40, 41, 42 and 43 in random initial remanence states. Magnetic core load 12 includes conventional windings on the magnetic cores thereof, not shown, for the practice of this invention, e.g., for a logic circuit, input and output windings, and for a memory circuit, set and sense windings. Feedback winding 44 on control magnetic core 36 is con nected across Zener diode 46. Over a range of current, a Zener diode provides a constant voltage output. The anode 48 of Zener diode 46 is connected to emitter 20 of driver transistor 14. Its cathode 50 is connected via diode 52 to base 18 of driver transistor 14. Diode 52 has its anode 54 connected to cathode 50 of Zener diode 46 and its cathode 56 connected to base 18. Reset winding 58 on control magnetic core 36 is connected to reset input terminal 60 and reset output terminal 62.

FIG. 2 presents an illustrative BH hysteresis curve 64 suitable for explaining the remanence states of magnetic load cores 40 to 43 of core load 12 and of control magnetic core 36. Hysteresis curve 64 has horizontal axis H which measures the driving ampere turns applied to a magnetic core and vertical axis B which measures the magnetic induction in the magnetic core. The hysteresis curve 64 is a substantially rectangular-loop with lower horizontal portion 66, right vertical portion 68, upper horizontal portion 70 and left vertical portion 7 2.

Points

76 and 78 on hysteresis curve 64 indicate the 13 and B remanence states, respectively, of an illustrative magnetic core. Illustratively, in logic and

memory circuits points

76 and 78 may be termed the 1 and conditions.

Points

80 and 82 on the H axis indicate the ampere-turns which are requisite for switching the illustrative magnetic core between B and B remanence states. In practice,

points

80 and 82 are selected at approximately twice the ampere-turns indicated by

points

81 and 83, respectively. Usually, the positions of

points

80 and 82 are selected as result of power and switching time considerations.

The circuit operation of the current driver presented in FIG. 1 will now be described. A positive going voltage input trigger signal 84 is applied to base 18 via input trigger signal terminal 26 and diode 28. The input trigger signal 84 causes transistor 14 to go from OFF to ON conduction. The collectonemitter current of transistor 14 flows through control winding 34 of control magnetic core 36 and the winding 37 of core load 12. The voltage which develops across control winding 34 is coupled into feedback winding 44 by transformer action. Zener diode 4'6 limits the magnitude of the voltage across feedback winding 44. The magnitude of the limited voltage is the breakdown voltage of the Zener diode 46. The emitter voltage of driver transistor 14 rises as a consequence of the voltage developed across core load 12 and control winding 34. However, since the feedback winding 44 is referenced to the emitter 20 voltage by being connected thereto and the voltage across the winding is limited to a particular maximum voltage by the Zener diode 46, a constant bias voltage equal to this maximum voltage is applied across the base 18 to emitter 20 junction. In practice, the Zener diode breakdown characteristic is selected to assure that the particular maximum voltage is always obtained. Therefore, a constant current pulse 89 flows through control winding 34 and winding 37 to energize the core load 12 until the control magnetic core 36 is switched from the remanence state 76 to point 31 on hysteresis curve 64. At point 91 driver transistor 14 is no longer forward biased across its base-emitter junction and its conduction terminates. Thereafter, the hysteresis curve of control magnetic core 36 returns to its remanence state 78. During the switching of control magnetic core 36, all the magnetic cores of core load 12 not initially in the 0 condition are switched thereto from the 1 condition. It will be readily apparent to those skilled in the art that diverse initial and final remanence states for core load 12 magnetic cores 40 to 43 are obtainable through control of their individual ampere-turns.

Input diode 28 allows the input trigger signal 84 to be applied to base 18 of driver transistor 14 and blocks the feedback voltage from feedback winding 44 from reaching input trigger signal terminal 26. In practice, if the feedback voltage is sufficient, diode 28 may be replaced by a capacitor. Feedback diode 52 prevents current flow from input trigger signal terminal 26 from flowing to feedback winding 44 during application of input trigger signal 84 thereto. In practice, if trigger signal 84 is of sufficient magnitude, diode 52 may be removed from constant current pulse circuit 10. Zener diode 46 assures a constant voltage across the base 18 to emitter 20 junction of driver transistor 14 during switching of core load 12. Negative going reset signal 90 applied to reset input and

output terminals

60 and 62 resets control magnetic core 36 via reset winding 58. Alternatively, in practice, the resetting of control magnetic core 36 can be accomplished by a constant bias current in reset winding 58. The number of turns of feedback winding 44 on control magnetic core 36 is adjusted so that the net ampere-turns on the control magnetic core 36 is less than the net ampere-turns of the core load 12 during switching thereof. This assures that core load 12 will be completely switched when the switching action of control magnetic core 36 terminates, i.e., the switching time of control magnetic core 36 is greater than the switching time of core load 12.

FIG. 3 presents another preferred embodiment of a current driver in accordance with this invention for resetting a magnetic core load. The constant current pulse driver 100 includes an NPN driver transistor 102 with collector 104, base 106 and emitter 108. In practice the driver 100 can readily be adapted to incorporate a PNP driver transistor instead of NPN driver transistor 102 by those skilled in the electronics art. Collector 104 is connected via resistor 112 to positive voltage source +V terminal 110. Base 106 is connected to input trigger signal terminal 114 via diode 116. Anode 118 of diode 116 is connected to input trigger signal terminal 114 and its cathode 120 is connected to base 106. Positive going input trigger signal 122 is applied to input trigger signal terminal 114. Emitter 108 of driver transistor 102 is connected to control winding on control magnetic core 132 via diode 136. Diode 136 has its anode 138 connected to emitter 108 and its cathode 140 connected to control winding 130. Conductor 134 is wound on core load 142 and is connected to ground 128.

Magnetic core load 142 includes illustrative magnetic cores 143 to 146 with additional conventional windings thereon, not shown, for the practice of this invention, e.g., for a logic circuit, input and output windings, and for a memory circuitry, set and sense windings. Cathode 140 of diode 136 is connected to terminal 148 of feedback winding 150 on control magnetic core 132. Terminal 152 of feedback control winding 150 is connected to base 106 of driver transistor 102 via parallel arrangement of capacitor 154 and resistor 156 in series with diode 158. Diode 158 has its anode 160 connected to capacitor 154 and its cathode 162 connected to base 106. The series path of resistor 164 and diode 166 is connected between

terminals

148 and 152 of feedback winding 150 on control magnetic core 132. Diode 166 has its anode 168 connected to resistor 164 and its cathode 170 connected to terminal 148. Reset winding 172 on control magnetic core 132 is connected to input reset terminal 174 and output reset terminal 176. Negative going reset signal 178 is applied to reset input and

output terminals

174 and 176.

The operation of the constant current pulse driver 100 presented by FIG. 3 is as follows:

Input trigger voltage signal 122 applied to input trigger signal terminal 114 is passed via diode 116 to base 106 of driver transistor 102 and causes collector-emitter current to flow therein. The collector-emitter current pulse 177 flows via diode 136 through control winding 130 on control magnetic core 132 and via conductor 134 through core load 142 to ground 128. The voltage developed across control winding 130 is coupled into feedback winding 150 by transformer action. The voltage at emitter 108 rises due to the voltage developed across control winding 130 and core load 142. However, since feedback winding 150 is referenced to emitter 108 via diode 136, the voltage across feedback winding 150 maintains the base 106 to emitter 108 junction at a substantially constant voltage until control magnetic core 132 is switched. Illustratively, control magnetic core 132 switches from point 76 to point 91 of the hysteresis curve 64 of FIG. 2. At point 91 driver transistor 102 is no longer forward biased and collector 104 emitter current conduction ceases.

The parallel arrangement of capacitor 154 and resistor 156 is in series via diode 158 with the input base resistance of driver transistor 102 and forms therewith a voltage divider network which controls the feedback voltage to the base 106. The charging of capacitor 154 causes a momentary voltage or current surge to base 106 and thereby improves the rise time of driver transistor 102. In practice, the magnitude of resistor 164 in parallel with feedback control winding 150 is controlled so that the net ampere-turns on control magnetic core 132 is such that the core load 142 completes its switching first. The magnitude of resistor 164 is established at a value such that the net ampere-turns of control magnetic core 132 is less than that of core load 142. Diode 116 prevents current flow at junction 163 from reaching input trigger signal terminal 114. In practice, if the feedback voltage is suificient diode 116 may be replaced by a capacitor. Diode 166 in series with resistor 164 prevents current flow in feedback win-ding 150 during resetting of control magnetic core 132. In practice, if the magnitude of resistor 164 is sufliciently large, diode 166 is not required. Diode 136 increases the effective reverse breakdown voltage of the emitter 108 to base 106 junction by acting as a voltage divider. In practice, where the normal reverse breakdown voltage of the emitter-base junction is not exceeded during circuit operation, diode 136 is not needed. Diode 158 in series with parallel arrangement of resistor 156 and capacitor 154 prevents flow of current into feedback winding 150 from input trigger signal terminal 114 during application of input trigger signal 12.2 thereto. In practice, if trigger signal 122 is of sufficient magnitude, diode 158 may be removed from constant current pulse circuit 100. Application of reset signal 178 to reset input and

output terminals

174 and 176 resets control magnetic core 132 via reset winding 172 thereon. Alternatively, in practice, the resetting of control magnetic core 132 can be accomplished by a constant bias current in reset winding 172. It will be apparent to those skilled in the art that the triggering action described above can be obtained by utilizing an auxiliary winding on the control magnetic core and applying thereto the input trigger signal.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. Constant current pulse driver for a variable impedance load comprising a current switching transistor having collector, base and emitter, said collector-emitter de fining a current path, a trigger signal input terminal connected via a first diode to said base, a control magnetic core with substantially rectangular hysteresis-loop characteristic, a control winding on said control core in series with said emitter-collector current path, a feedback winding on said control magnetic core, voltage reference means connected to said feedback winding and said collector-emitter current path for referencing said base and emitter at a controllable potential during said time variation of said variable impedance load, a second diode, said feedback winding being connected to said base via said second diode, said first and second diodes being poled so that said trigger signal is blocked from applying current to said feedback winding and said voltage developed across said feedback winding is blocked from said input terminal, a reset winding on said control core, reset signal means connected to said reset winding adapted to cause reset current to flow therein thereby resetting said control core to its initial remanence state, said voltage reference means including a Zener diode connected across said feedback winding, said Zener diode being poled to reference the base and emitter to said Zener diode breakdown voltage.

2. Constant current pulse driver for a variable impedance load comprising a current switching transistor having collector, base and emitter, said collector-emitter defining a current path, a trigger signal input terminal connected via a first diode to said base, a control magnetic core with substantially rectangular hysteresis-loop characteristic, a control winding on said control core in series with said emitter-collector current path, a feedback winding on said control magnetic core, voltage reference means connected to said feedback winding and said collector-emitter current path for referencing said base and emitter at a controllable potential during said time variation of said variable impedance load, a second diode, said feedback winding being connected to said base via said second diode, said first and second diodes being poled so that said trigger signal is blocked from applying current to said feedback winding and said voltage developed across said feedback winding is blocked from said input terminal, a reset winding on said control core, reset signal means connected to said reset winding adapted to cause reset current to flow therein thereby resetting said control core to its initial remanence state, said voltage reference including a Zener diode connected across said feedback winding, said Zener diode being poled to reference the base and emitter to said Zener diode breakdown voltage, and said variable impedance load including a plurality of magnetic cores, each of said cores having a substantially rectangular hysteresis loop and a random initial remanence state and the time variation for switching each of said load magnetic cores between its respective remanence states being variable.

3. A current driver for resetting a magnetic core load including in combination an input terminal, means for applying to said input terminal an input trigger signal, a diode, a driver transistor having a collector, a base and an emitter, said input terminal connected to said via said diode, said diode being connected in the forward direction between said input terminal and said base, a resistor, a source of voltage for said transistor, said collector being connected to said voltage source via said resistor, a core load including a plurality of magnetic cores therein, a control magnetic core, a control winding on said control core, a feedback winding on said control core, said control winding being magnetically coupled to said core load, a Zener diode connected across said feedback winding, said feedback winding being connected to said emitter to reference said base-emitter junction at said Zener diode breakdown potential, a second diode, said Zener diode being connected to said base via said second diode poled in the forward direction.

References Cited by the Examiner UNITED STATES PATENTS 2,920,213 1/1960 Elias 307-88 2,997,600 8/1961 Hilberg et al. 307-88 3,134,023 5/1964 Russell 307-88 3,140,400 7/1964 Shansky 30788 IRVING L. SRAGOW, Primary Examiner.

Claims

1. CONSTANT CURRENT PULSE DRIVER FOR A VARIABLE IMPEDANCE LOAD COMPRISING A CURRENT SWITCHING TRANSISTOR HAVING COLLECTOR, BASE AND EMITTER, SAID COLLECTOR-EMITTER DEFINING A CURRENT PATH, A TRIGGER SIGNAL INPUT TERMINAL CONNECTED VIA A FIRST DIODE TO SAID BASE, A CONTROL MAGNETIC CORE WITH SUBSTANTIALLY RECTANGULAR HYSTERESIS-LOOP CHARACTERISTIC, A CONTROL WINDING ON SAID CONTROL CORE IN SERIES WITH SAID EMITTER-COLLECTOR CURRENT PATH, A FEEDBACK WINDING ON SAID CONTROL MAGNETIC CORE, VOLTAGE REFERENCE MEANS CONNECTED TO SAID FEEDBACK WINDING AND SAID COLLECTOR-EMITTER CURRENT PATH FOR REFERENCING SAID BASE AND EMITTER AT A CONTROLLABLE POTENTIAL DURING SAID TIME VARIATION OF SAID VARIABLE IMPEDANCE LOAD, A SECOND DIODE, SAID FEEDBACK WINDING BEING CONNECTED TO SAID BASE VIA SAID SECOND DIODE, SAID FIRST AND SECOND DIODES BEING POLED SO THAT SAID TRIGGER SIGNAL IS BLOCKED FROM APPLYING CURRENT TO SAID FEEDBACK WINDING AND SAID VOLTAGE DEVELOPED ACROSS SAID FEEDBACK WINDING IS BLOCKED FROM SAID INPUT TERMINAL, A RESET WINDING ON SAID CONTROL CORE, RESET SIGNAL MEANS CONNECTED TO SAID RESET WINDING ADAPTED TO CAUSE RESET CURRENT TO FLOW THEREIN THEREBY RESETTING SAID CONTROL CORE TO ITS INITIAL REMANENCE STATE, SAID VOLTAGE REFERENCE MEANS INCLUDING A ZENER DIODE CONNECTED ACROSS SAID FEEDBACK WINDING, SAID ZENER DIODE BEING POLED TO REFERENCE THE BASE AND EMITTER TO SAID ZENER DIODE BREAKDOWN VOLTAGE.