Automatic control of voltage supply to direct current moto

Barniskis, W. A.

Fink, J. W.

English

NASA Technical Reports Server

May27, 1969 JAMES E. WEBB 3,446,992 ADMINISTRATOR OF THE NATIONAL AERONAUTICS 
A N D  SPACE ADMINISTRATION 
BUS VOLTAGE COMPENSATION CIRCUIT FOR 
CONTROLLJNG DIRECT CURRENT MOTOR 
Filed Dec. 27, 1966 
https://ntrs.nasa.gov/search.jsp?R=19690030602 2020-03-16T19:01:47+00:00Z
3,446,992 United States Patent Office Patented May 27, 1g6g 
1 
3,446,992 
BUS VOLTAGE COMPENSATION CIRCUIT FOR 
CONTROLLING DIRECT CURRENT MOTOR 
James E. Webb, Administrator of the National Aero- 
nautics and Space Administration with respect to an 
invention of Walter A. Barniskis and John W. Fink, 
both of Minneapolis, Minn. 
Filed Dec. 27,1966, Ser. NO. 605,102 
Int. C1. HQ3k 1/16, 51159 
U.S. C1. 307-265 3 Claims 
ABSTRACT OF THE DISCLOSURE 
A control circuit for a~utomatically compensating for 
fluctuations in voltage supply to a D.C. motor for which 
the on-time is made to vary with an input signal. The 
control circuit comprises a relaxation oscillator formed 
of a unijunction transistor, the output pulses of which 
are fed through an isolation transistor to a monostable 
multivibrator which controls a switching transistor in 
series with the motor winding and motor voltage source. 
The oscillator output pulses control the frequency of 
periods during which current flows through the motor 
winding and a source of input signals also fed to  the 
monostable multivibrator varies the period during which 
current flows through the winding. To compensate for 
variations in the motor winding voltage, a feedback cir- 
cuit is coupled from the motor voltage source to the uni- 
junction transistor and the motor voltage SOUTCe is con- 
nected to the multivibrator at the input signal terminal. 
If the motor voltage source varies, the frequency and 
duration of the operational period of the motor winding 
is varied to maintain a constant motor current-time 
characteristic. 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 52 U.S.C. 4257). 
This invention relates in general to control circuits 
and more particularly, to a bus voltage compensation cir- 
cuit for providing a constant current-time characteristic 
through a load. 
In motor control circuits, the on-time of the motor may 
be made to vary with an input signal, thus producing a 
current-time characteristic which is directly related to 
the input signal, the current-time characteristic being 
the relationship of quantity of current supplied to  the 
motor winding relative to a time period. However, fluc- 
tuations of the bus voltage would alter the motor current- 
time characteristics causing them to be a function not 
only of the input signal, bat also of the bus voltage. 
While bus voltage regulator circuits for extremely ac- 
curate voltage regulation are well known, such circuits 
are usually complex. 
In order to  provide a constant current-time output 
characteristic for a D.C. motor winding in accordauce 
with an input signal, the present invention automatically 
corrects for bus voltage variations while simultaneously 
eliminating the need for prior art regulation circuits. A 
coilstant current-time characteristic is herein considered 
a current-time characteristic which is unaltered by Buc- 
tuations in the motor voltage supply. The invention 
utilizes the varying bus voltage in a novel feedback ar- 
rangement so that fluctuations of the bus voltage are 
automatically compensated for to provide the desired 
current-time oatput characteristic at the motor winding. 
More particularly, the invention comprises a D.C. 
motor having la winding whose current-time characteristic 
is varied by a control circuit. The circuit comprises a 
2 
relaxation oscillator formed of a mijunction transistor. 
The output pulses of the oscillator control the frequency 
of the periods during which the current flows through the 
motor winding. Output pulses from the oscillator are fed 
through an isolation transistor to a monostable multi- 
vibrator. Also fed to the monostable multivibrator is a 
source of input signals which varies the period during 
which current flows through the motor winding. The 
output of the multivibrator is fed to a switching tran- 
sistor. In order to  compensate for variations in the motor 
winding voltage, a feedback circuit is coupled from the 
motor voltage source to the unijunction transistor. Fur- 
ther, the motor voltage source is connected to the multi- 
vibrator at the input signal terminal. As the motor volt- 
15 age source varies, the frequency and duration of the 
operational period of the motor winding is varied. The 
resultant output at the motor winding is a constant cur- 
rent-time characteristic. 
The advantage of this invention, both as to its con- 
20 struction and mode of operation, will be readily ap- 
preciated as the same become better understood by refer- 
ence to the following detailed description when considered 
in connection with the accompanying drawing wherein: 
FIG. 1 is a circuit of the navel motor control circuit; 
FIGS. 2a and 2b are graphical displays of the current- 
time characteristics of the circuit of FIG. 1. 
Referring now to FIG. 1, there is shown the novel 
motor control circuit in accordance with this invention. 
30 Input signals are applied to an input terminal 12 to vary 
the current-time characteristics of a load such as a D.C. 
motor 14. 
The circuit further comprises a relaxation oscillator 
comprising a unijunction transistor 16 having an emitter 
35 18, a first base 22, and a second base 24. A charging 
circuit for the oscillator comprises a resistor 25 which 
is connected between a source of positive potential (B+) 
and the emitter 18, and a capacitor 26 which is connected 
between the emitter 18 land ground. 
The first unijunction transistor base 22 is connected 
to both the source of positive reference potential through 
a resistor 28 and to  a motor voltage source at terminal 
32 through a resistor 34. The second unijunction tran- 
sistor base 24 is connected through an output resistor 36 
45 to ground. Output signals from the base 24 are coupled 
to an isolation transistor 38 at its base 401. The transistor 
38 further comprises an emitter 42, which is Connected 
to  ground, and a collector 44. 
Output signals from the transistor 38 are coupled to a 
50 monostable multivibrator comprising a first transistor 46 
having a base 48, an emitter 52, and la collector 54, and 
a second transistor 56 having a base 58, an emitter 62, 
and a collector 64. The collector 54 of transistor 46 is 
connected to the collector 44 of the transistor 38, and 
55 also to the base 58 of transistor 56 through a capacitor 
66. The emitter 52 of the transistor 46 is connected to 
ground, and the base 48 is connected through a resistor 
68 to the collector 64 of transistor 56. Emitter 62 of 
transistor 56 is connected to  ground. The input terminal 
60 12 is connected through a resistor 7% to the junction of 
the capacitor 66 and the collector 54 of transistor 46. The 
collector 64 of transistor 56 is also connected through a 
biasing resistor 74 to the source of positive potential. 
Further, the base 58 of transistor 56 is connected through 
Output signals from the multivibrator are coupled 
from the collector 64 to a switching transistor 7'8 at its 
base $2. The transistor 78 further comprises an emitter 
84 which is connected to  ground, and a collector 86 which 
is connected through the motor winding 88 to the motor 
voltage terminal 32. 
25 and 
40 
65 a resistor 76 to the terminal 32. 
3,446.992 
3 
With the foregoing in mind, operation of the circuit 
of FIG. 1 with the compensating resistor 34 omitted from 
the circuit, and with the resistor 76 connected to the 
source of positive potential rather than the terminal 32 
is as follows: 
The capacitor 26 charges through the resistor 25 for a 
sufficient value until the unijunction transistor 16 becomes 
conductive, producing a positive pulse at the base 40 of 
transistor 38, causing the transistor 38 to  conduct. With 
the transistor 388 conductive, the capacitor 66 discharges 
through the transistor 58 and causes transistor 56 to be- 
come non-conductive and transistor 46 to become con- 
ductive. With transistor 56 non-conductive, the voltage at 
its collector 64 starts to  rise, causing transistor 78 to 
become conductive, allowing current to flow through the 
motor winding 88. Transistor 56 remains non-conductive 
and transistor 78 remains conductive in accordance with 
the signal applied to the terminal 12. The monostable 
multivibrator then returns to  its stable state (the transistor 
56 conductive and transistor 46 non-conductive), and 
current no longer flows through the motor winding 88 
until the next pulse from the relaxation oscillator is ap- 
plied to  transistor 38. The current-time characteristic 
through the winding 88 is as depicted in FIG. 2a. 
Should the voltage at  the terminal 32 rise, of course, a 
greater current would flow through the motor winding 
88 for a given period of time. Considering now the circuit 
of FIG. 1 with the resistor 34 in the circuit, and the re- 
sistor 76 connected to the terminal 32, as the voltage at 
terminal 32 starts to  rise, the voltage at the base 22 of 
mijunction transistor 16 also starts to rise and capacitor 
26 must charge h r  a longer time before the unijunction 
transistor becomes conductive. Thus, a greater voltage 
at terminal 32 will decrease the frequency of the pulses 
from the unijunction transistor and cause the on-time of 
the transistor 78 t o  decrease. Further, the rise in voltage 
at  the terminal 32 causes the capacitor 66 to reach the 
turn-on voltage of transistor 56 faster, reducing the on- 
time of the transistor 78. The net effect of the increase 
of the voltage at terminal 32 is t o  decrease the frequency 
, 
4 
vention, and that it is intended t o  cover all changes and 
modifications of the examples of the invention herein 
chosen for the purpose of the disclosure which do not 
constitute departures from the spirit and scope of LIe 
invention. 
What is claimed and desired to be secured by Letters 
Patent is: 
1. A control circuit for providing a constant current- 
time characteristic through a load in accordance with an 
input signal comprising: 
an oscillator for producing output pulses whose fre- 
quency controls the periods during which current 
flows through said load, said oscillator comprising a 
unijunction transistor; 
switching means for controlling the duration of said 
periods, said oscillator output pulses and said input 
signal being coupled to said switching means; 
a source of D.C. voltage coupled tu said load; 
means coupling said switching means to  said load; 
means for coupling said D.C. voltage t o  said oscillator 
by connecting said D.C. voltage to a base of said 
unijiunction transistor for varying the frequency of 
said periods in accordance with variations in said 
D.C. voltage; 
said switching means comprising a monostable multi- 
vibrator, said D.C. voltage being coupled to said 
monostable multivibrator for varying the current 
through said load in accordance with variations in 
said D.C. voltage. 
2. A control circuit in accordance with claim 1 wherein 
30 said switching means further comprises an isolation tran- 
sistor, said isolation transistor coupling said relaxation 
oscillator to  said monostable multivibrator. 
3. A control circuit in accordance with claim 2 and 
further comprising a switching transistor having a first 
35 stable state and a second stable state, said switching tran- 
sistor being coupled between said monostable multi- 
vibrator and said load, said monostable nultivibrator 
controlling said stable states of said switching transistor. 
5 
lo 
l5 
2o 
25 
40 
and pulse width of the motor current pulses. Thus, the References Cited 
UNITED STATES PATENTS current versus time characteristic remains constant, as 
can be seen by the curve of FJG. 2b. 
It should be further appreciated that the circuit may 29714@3 811955 Van ----------- 317-137 
be used to  energize the winding of the motor in one 45 611965 Gargani ------_- 318-341 XR 
direction and obtain rotation in one direction of the 3,214,666 1011065 ClerC ---------- 318-341 XR 
motor. A second channel similar to  the one disclosed may 3,223,912 1211965 Sheheen ----------- 318-341 
be provided so as to receive opposite polarity signals a t  3,358,206 1211967 Thiele ---_-___-____ 318-341 
the terminal 12 so as to reverse the energized motor wind- 3,378,745 411968 James ---_-_---- 318-341 XR 
ing and thus cause opposite rotation thereof. 
current through a motor winding, it should be understood, 
of course, that the cirauit could be utilized where a con- 
3,191,113 
While the circuit has been described as controlling the 50 JOHN s. HEYMAN, Primory Examiner. 
JOHN ZAZWORSKY, ~~~i~~~~~ ~ ~ ~ i ~ ~ ~ .  
stant current-time characteristic is to be supplied pe- 
riodically to a load from a varying voltage source. 
U.S. C1. X.R. 
It should be further understood that the foregoing dis- 55 307-271, 297; 318-18, 138, 341, 345; 331-111 
closure relates only 'to preferred embodiments of the in- 


Bus voltage compensation circuit for controlling direct current motor

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