Interrogator and current driver circuit for combination with transistor flip-flop circui

Chong, C. F.

Nelson, C. A.

English

NASA Technical Reports Server

June 23, 1970 R. C. SEAMANS, JR 395 
DEPWTY ADMINISTRATOR OF THE NATIONAL 
AERONAUTICS AND SPACE ADMlNlSTRATION 
Filed July 29, 1966 
FLIPFLOP INTERROGATOR AND BI-POLAR CURRENT DRIVER 
_. 
41 
57 
51 
53 
59 
15 17 
23 *59 
INVENTORS 
C. 
c. 
https://ntrs.nasa.gov/search.jsp?R=19710010072 2020-03-17T02:44:14+00:00Z
3,s 17,22 1 United States Patent Office June23,197Q 
1 
3,517,221 
C NT DRIVER 
Robert C. Seamans, Jr., Deputy Administrator of the Na- 
tional Aeronautics and Space Administration, with re- 
spect to an invention of Carlos F. Chong and Charles 
A. Nelson, both of Philadelphia, Pa. 
Filed July 29,1966, Ser. No. 568,987 
In& CI. H03k 3/12 
US. C1. 307-289 2 Claims 
FLIPFLOP ENTElRROGATQR AND BI-POLAR 
10 
ABSTRACT O F  THE DISCLOSUIW 
An interrogator and current driver circuit for com- 
bination with a transistor flipflop circuit, wherein the 
flipflop operates nominally in a saturated state at very 
low levels of collector current but wherein, during inter- 
rogation, the load resistance of the conducting transistor 
is reduced and wherein the conducting transistor is pro- 
vided with additional base drive to sustain higher satura- 2o 
tion currents so that the conducting transistor of the flip- 
flop operates as the current driver amplifier. 
The invention described herein was made in the per- 25 
formance of work under a NASA contract and is subject 
to the provisions of Section 30.5 of the National Aeronau- 
tics and Space Act of 1958, Public Law 85-568 (72 Stat 
435; 42 USC 2457). 
This invention relates to current driver circuits and 3o 
more particularly to bi-polar current driver circuits. 
Current drivers are electronic circuits that generate a 
current pulse for driving electronic circuits or devices. 
The driver is normally under the control of a control 
circuit and may generate its current pulses in accordance 35 
with the overall timing of a system, for example. Or, the 
driver may generate a high level pulse in accordance with 
a low level input pulse. 
The output pulses from the driver may be utilized to 
control the input of information into a register. Or, the 40 
driver may be used to control the input of information 
into the cores of a matrix memory system. Further, the 
output signal from the driver can be used to control logic 
circuits. Hence, a current driver circuit has many uses in 
A bi-polar current driver is one that provides a bi- 
polar output in accordance with an input signal. That 
is, a bi-polar current driver can be controlled to gen- 
erate either positive or negative pulses. A logic circuit 
may be used to control the polarity of the output from 50 
the bi-polar driver. The timing of the output may then 
be controlled by a control pulse from an independent 
source. This system will then generate a pulse of a par- 
ticular polarity at a particular time. 
The bi-polar current driver has many uses in electronic 55 
circuits. It may be used to provide a current pulse to the 
cores of a memory matrix. It may be used to provide a 
bidirectional current flow to operate logic systems. Or, it 
may be used to turn on and turn off various switching 
circuits as desired. For example, a positive output pulse 60 
may turn on a particular circuit and a negative pulse may 
turn off the circuit. 
The prior art devices for performing a bipolar current 
driver function have required separate circuits to generate 
bi-polar pulses. That is, one circuit to generate negative 65 
pulses and another circuit to generate positive pulses. 
These circuits have required the use of a large number 
of electronic components connected in complex circuit 
arrangements. A coupling network has been used to con- 
nect the positive and negative drivers to a common out- 70 
put. In addition, prior art control devices for current 
electronic systems and networks. 45 
- ~~ ~ - ~ ~ 
drivers have gener'ally required relatively high currents comprises a transformer 39 having a &st primary winding 
2 
to operate. This disadvantage has resulted in power loss 
as well as a requirement for electronic components that 
operate at these current levels. 
Hence, the primary disadvantages of the prior art reside 
in complex circuits and components, and in the high level 
current inputs necessary to operate the control circuits for 
the bi-polar current drivers. 
Therefore, it is an obect of this invention to provide a 
new and improved bi-polar current driver circuit. 
It is a further object of this invention to provide a new 
and improved bi-polar driver circuit wherein the logic 
circuit controlling the ourrent driver operates at a much 
lower current level than does the current driver. 
In accordance with a principle of the invention the out- 
puts from a low input current bistable flip-flop are con- 
nected to a transformer coupling circuit. The transformer 
coupling circuit is also connected to a current pulse 
source. When a current pulse is applied to the transformer 
coupling network an output is produced. The polarity of 
the output is dependent upon the state of the bistable 
flip-flop. 
It will be appreciated that the foregoing is a simple de- 
vice requiring the use of a conventional flip-flop circuit 
in conjunction with a transformer coupling network. In 
addition, the mere application of an input pulse generates 
a bipolar output. Moreover, the polarity of the output is 
dependent upon the state of the flip-flop. Hence, the de- 
vice is simple and uncomplicated and provides a bi-polar 
current for driving electronic circuitry. 
The foregoing objects and many of the attendant ad- 
vantages of this invention will become more readily ap- 
preciated as the same becomes better understood by ref- 
erence to the following detailed description when taken 
in conjunction with the accompanying drawings wherein: 
The figure is a schematic diagram of a current driver 
constructed in accordance with the invention. 
Turning now to the drawing wherein like reference 
numbers designate like parts throughout the several views. 
The circuit illustrated comprises a bistable flip-flop gen- 
erally indicated at 11 and a driver circuit generally indi- 
cated at 13. The bistable flip-flop comprises a first NPN 
transistor 15 and a second NPN transistor 17. The emit- 
ter of each of the transistors is grounded. The base of the 
first transistor 15 is connected to the cathode of a first 
diode 19; and the anode of the first diode is connected 
to the cathode of a second diode 21. The anode of the 
second diode 21 is connected to the anode of a third di- 
ode 23; and the cathode of the third diode 23 is connected 
to the collector of the second transistor 17. Similarly, a 
fourth diode 25 has its cathode connected to the base of 
the second transistor 17. The anode of the fourth diode is 
connected to the cathode of a fifth diode 27. The cathode 
of the fifth diode is connected to the cathode of a sixth di- 
ode 29; and the anode of the sixth diode is connected to 
the collector of the first transistor 15. 
The junction between the second and third diodes is 
connected through a first resistor 31 to a voltage source 
VI. Similarly, the junction between the lifth diode 27 and 
the sixth diode 29 is connected through a second resistor 
33 to the voltage source VI. Further, the junction be- 
tween the second diode and the first resistor is connected 
to an input terminal 35; and, the junction between the 
fifth diode and the second resistor is connected to a sec- 
ond input terminal 37. 
The foregoing has described a transistorized bistable 
flip-flop wherein a signal applied to one input 35 sets the 
bistafble flip-flop in one state; while a signal applied to the 
second input 37 flips the flip-flop to its other state. A bi- 
stable flip-flop of this type will operate at a current level 
as low as 60 microamperes. 
The current driver circuit nenerallv illustrated at 13 
the conector of the first transistor 15. Similarly, the other 
end of the second primary winding.43 is connected to one 
end of a fourth resistor 57; the other end of the fourth 
resistor is connected to the anode of an eighth diode 59 at 
a junction B. The cathode of the eighth diode is con- 
nected to the collector of the second transistor 16. The 
junction A between the third resistor and the seventh di- 
ode is connected to one end of a fifth resistor 61. The 
other end of the fifth resistor is connected to the anode 
of a ninth diode 63. The cathode of the ninth diode is 
connected to the junction between the fifth and sixth di- 
odes. Similarly, the junction B between the fourth re- 
sistor and the eighth diode is connected to one end of a 
sixth resistor 65; and the other end of the sixth resistor 
is connected to the anode of a tenth diode 67. The cathode 
of the tenth diode is connected to the junction between 
the second and third diodes. 
It is to be understood that the first and second pri- 
mary windings 41 and 43 are wound in the same direc- 
tion with respect to the secondary winding 45. Hence, 
when a pulse is applied to the pulse input terminal 51 and 
passes through the first primary winding 41 it will create 
a current flow in one direction in the secondary winding. 
And, when the pulse flows through the second primary 
winding 43 it mi create a current flow in the opposite 
direction in the secondary winding. Further, when the 
pulse flows through both primary windings it will create 
a current flow in the secondary winding in accordance 
with which primary winding has the greatest current flow- 
ing through it. 
When the pulse input terminal 51 is at ground, the 
seventh 55, eighth 59, ninth 63, and tenth 67 diodes 
are back biased; therefore, the bistable flip-flop 11 operates 
at its normal low current level. That is, the back bias 
prevents current from the bias source V1 to flow in the 
driver circuit 13 and hence, allows the bistable flip-flqp 
to operate as though the driver circuit does not exist. 
When an input pulse is applied to the pulse input 
terminal 51 it flows through both of the primary wind- 
ings and through the circuitry connected thereto. How- 
ever, due to the fact that the first and second transistors 
are connected to the outside ends of the windings and 
because one is on and the other is off, more current 
flows through one winding than the other. This current 
flow is coupled to the secondary winding 45 and deter- 
mines the direction of current flow through that wind- 
ing. Specifically, when an input pulse is applied to the 
pulse input terminal 51 and the first transistor is turned 
on, the voltage at junction A only rises to a low value 
while the voltage at junction B rises to a much higher 
relative value. The connection of the windings 41 and 43 
to transistors 15 and 17 through diodes 55 and 59 re- 
spectively provide a means for sensing which transistor 
is conducting. This configuration enables diode 55 and 59 
to act as voltage sensitive switches for connecting addi- 
tional impedance elements in parallel with the coPector 
load of their respective conducting transistor. Specifically, 
the load impedance of transistor 15, after switching, in- 
cludes resistor 53, winding 41 and the impedance of the 
pulse source connected to 51 in parallel with the nominal 
load impedance, i.e., diode 29, resistor 33 and source 
impedance of V1. By placing these additional impedance 
elements in parallel with the collector, the effective load 
resistance on the collector of transistor 15 is reduced. The 
3,517,221 
3 4 
41 and a second primary winding 43. The transformer 
39 has a single secondary winding 45 connected to a pair 
of terminals 47. One end of each of the two primary 
windings are connected together at a junction 49; this 
junction is also connected to a pulse input terminal 5P; 
terminal 51 provides the means for receiving interrogation 
timing signals to initiate an interrogation interval. 
The other end of the first primary winding 41 is con- 
nected to one end of a third resistor 53 whose other end 
is connected to the anode of a seventh diode 55 at a junc- 
tion A. The cathode of the seventh diode is connected to 
' 
design value of these additional resistances switched in 
by diode 55 is selected so that the effective load resistance 
results in a load line whioh enables a collector current 
of sufficient magnitude to drive other electronic ele- 
ments, Le., a collector current of 30 milliamperes as com- 
pared with the nominal 60 microamperes. 
In order to retain the transistor 15 in a saturated con- 
dition at the higher collector current level, as it can be 
seen from a standard saturated mode graph, is necessary 
to provide an increased base drive. This drive is provided 
by the high VolQe at junction B which is Provided by 
the pulse at terminal 51. That is, the voltage at junction 
B provides additional bias to the base of the first tran- 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
70 
75 
sisior 15 and the current path through that transistor re- 
mains high because it has a low resistance value due to 
its remaining saturated. Moreover, the second transistor 
remains non-conductive because the voltage at junction A 
is insufficient to turn it on. 
In a similar manner if the second transistor is turned 
on and the first transistor is turned off a large current 
will flow through the second primary winding 43 and a 
small current will flow through the first primary winding 
41, This small current flow will increase the bias on the 
base of the second transistor and keep it in saturation. 
This will allow an increased current to flow through the 
second secondary winding. 
In this manner whether the first or second transistors 
are turned on determines which primary winding will re- 
ceive the majority of the current flow. This mrrent will 
then determine the direction of the pulse output at the 
output terminals 47. Hence, by controlling the state of 
the flip-flop the system provides a controlled bi-polar 
high current output. 
The output is controlled by a low current control net- 
work. Specifically, a current in the microampere range 
will control the transistors 15 and 17. However, the cur- 
rent output pulse can be in the milliampere range. More 
specifically, in one operable embodiment of the invention 
a bistable flip-flop that operates on 60 microamperes has 
been used to control a 30 milliampere output pulse. 
What is claimed is: 
1. In a flipflop interrogation and driver circuit in com- 
bination with a low current level transistor flipflop for 
generating a high level bi-polar driving current represent- 
ative of said flipflop state, each transistor of said flipflop 
having collector load impedance and base drive selected to 
maintain the conducting transistor of said flipflop at very 
small values of collector current during non-interrogation 
intervals, the improvement comprising: 
terminal means for receiving interrogation timing con- 
trol signals to initiate an interrogation interval; 
sensing means for ascertaining the conducting transistor 
of said flipflop, said sensing means being coupled to 
said interrogation timing terminal means for ascer- 
taining the state of said flipflop during said interroga- 
tion interval; 
switching means, said switching means being respon- 
sive to said sensing means for connecting additional 
impedance elements in parallel with said collector 
load of said conducting transistor, said additional 
impedance elements including a primary winding of 
a transformer, said switching means being coupled to 
said interrogation timing terminal means; 
biasing means, said biasing means being coupled to said 
interrogation timing terminal means for provid& 
additional base drive to said conducting transistor 
exclusively during said interrogation interval thereby 
enabling said conducting transistor to operate in a 
higher level saturation condition, whereby said con- 
ducting transistor will cause said high level bi-polar 
current to flow in said primary of said transformer 
in a selected direction, said selected direction of cur- 
rent flow through said primary of said transformer 
being indicative of the state of said flipflop. 
3,517,221 
5 
2. Apparatus as defined in claim 1 wherein said switch- 
wherein said primary winding of said additional im- 
pedance element has a centrally located tap therein, 
a first diode of said pair of diodes being coupled be- 
tween the collector of said conducting transistor of ' 
said ffipffop and a first end of said center tapped 
transformer, the second diode of said pair of diodes 
being coupled between the collector of said non- 
conducting transistor of said flipflop and a second 1o 
end of said center tapped transformer; 
said biasing means comprises a path of continuity from 
said centrally located tap of said transformer to each 
base electrode of said flipflop transistors, and 
said terminal means for receiving interrogation timing 16 
control signals being connected to said centrally lo- 
cated tap of said transformer. 
ing means comprises a pair of diodes, and 
6 
References Cited 
UNITED STATES PATENTS 
2,883,525 4/1959 Curtis _ _ _ _ _ _ _ _ _ _ _ _ _ _  328-196 
2,898,479 8/1959 McElroy _ _ _ _ _ _ _ _ _ _ _  307-282 
2,977,485 3/1961 Olsen _ _ _ _ _ _ _ _ _ _ _  307-282 X 
3,290,605 12/196& Humphrey _ _ _ _ _ _ _  328-206 X 
3,307,045 2/1967 Jaivinen _ _ _ _ _ _ _ _ _  328-206 X 
3,334,292 8/1967 King et a). _ _ _ _ _ _ _ _  307-262 X 
STANLEY T. KRAWCZEWICZ, Primary Examiner 
U.S. C1. X.R. 
307-262, 269, 270, 282; 328-63, 65, 206 


Flipflop interrogator and bi-polar current driver Patent

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