U.S. patent number 3,864,608 [Application Number 05/361,959] was granted by the patent office on 1975-02-04 for combination monostable and astable inductor driver.
This patent grant is currently assigned to MKC Electronics Corporation. Invention is credited to Eugene Brooks Lilly, Victor M. Mathews, Jr., James M. Normile.
United States Patent |
3,864,608 |
Normile , et al. |
February 4, 1975 |
COMBINATION MONOSTABLE AND ASTABLE INDUCTOR DRIVER
Abstract
A driver is disclosed that is particularly adapted to deliver
excitation to solenoids characterized by a high ratio of pull-in
current to holding current. In order to minimize the continuous
current rating of a solenoid required in a given application, the
solenoid is pulsed with holding current after pull-in is effected.
The driver employs solid state timing circuitry having monostable
and astable modes of operation controlled by capacitors provided
with independent charging and discharging circuits. After the
initial, monostable mode in which the driving excitation is
uninterrupted, the timing circuitry automatically goes into the
astable mode to pulse the solenoid in accordance with a
predetermined duty cycle which may be set at either less than or
greater than fifty percent throughout a wide range as required.
Inventors: |
Normile; James M. (Kansas City,
KS), Mathews, Jr.; Victor M. (Leawood, KS), Lilly; Eugene
Brooks (Overland Park, KS) |
Assignee: |
MKC Electronics Corporation
(Kansas City, KS)
|
Family
ID: |
23424109 |
Appl.
No.: |
05/361,959 |
Filed: |
May 21, 1973 |
Current U.S.
Class: |
361/154;
361/194 |
Current CPC
Class: |
H01H
47/325 (20130101) |
Current International
Class: |
H01H
47/22 (20060101); H01H 47/32 (20060101); H01h
047/32 () |
Field of
Search: |
;317/154,DIG.4,148.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hix; L. T.
Attorney, Agent or Firm: Chase; D. A. N.
Claims
Having thus described the invention, what is claimed as new and
desired to be secured by Letters Patent is:
1. In actuator apparatus employing a solenoid characterized by a
relatively high ratio of required pull-in current to required
holding current, a driver for operating said solenoid
comprising:
supply terminal means connected to said solenoid for supplying the
latter with operating potential;
electrically responsive, bistate switching means connected with
said terminal means for applying said potential thereto when said
switching means is in a first operational state, and for
interrupting application of said potential to said terminal means
when said switching means is in a second, normal operational state;
and
control means coupled with said switching means for delivering an
electrical control signal thereto in accordance with a timing
program selected to provide the pull-in current requirements of
said solenoid and hold the solenoid following pull-in,
said control means upon activation thereof causing said switching
means to initially assume said first state for a predetermined,
uninterrupted time period at the outset of said program
corresponding to said pull-in requirements, and thereafter cycling
said switching means between said first and second states to
provide a pulse width and spacing at said terminal means which
supplies sufficient holding current to the solenoid,
said control signal having first and second levels and said control
means delivering said signal at said first level during said time
period at the outset of said program and thereafter cycling said
signal between said first and second levels to cause said switching
means to assume said first and second states thereof respectively
in response to said first and second levels of the signal,
said control means including first capacitor means, charging and
discharging circuit means connected with said first capacitor
means, operating means responsive to predetermined minimum and
maximum voltages developed across said first capacitor means for
causing the latter to charge via said circuit means when the
voltage across said first capacitor means falls to said minimum,
and to discharge via said circuit means when said voltage rises to
said maximum, and output means for delivering said control signal
at said first level during charging of the first capacitor means
and at said second level during discharge thereof, whereby said
first capacitor means, charging and discharging circuit means, and
operating means control said pulse width and spacing at said
terminal means to provide a predetermined duty cycle following said
uninterrupted time period at the outset of said program,
said control means being provided with second capacitor means of
substantial capacitance, and means electrically connecting said
second capacitor means with said circuit means during charging
operation thereof but electrically isolating said second capacitor
means therefrom during discharging operation of said circuit means,
whereby upon said activation of the control means both the first
and second capacitor means charge over a time duration terminating
when said voltage reaches said maximum, said time duration defining
said uninterrupted time period at the outset of said program.
2. Driver apparatus for delivering electrical excitation which is
uninterrupted during an initial period followed by intermittent
delivery at a predetermined duty cycle, said apparatus
comprising:
supply terminal means for delivering said excitation to an external
load connected thereto;
electrically responsive, bistate switching means connected with
said terminal means for applying said excitation thereto when said
switching means is in a first operational state, and for
interrupting application of said excitation to said terminal means
when said switching means is in a second, normal operational state;
and
control circuitry coupled with said switching means and having
first and second electrical output levels causing said switching
means to assume said first and second states thereof
respectively,
said control circuitry having monostable and astable modes of
operation and, upon activation thereof, initially operating in said
monostable mode followed by continuous operation in said astable
mode,
said control circuitry in said monostable mode delivering an output
signal at said first level for said initial period and, in said
astable mode, cycling said output signal between said first and
second levels in accordance with a pulse width and spacing
corresponding to said predetermined duty cycle, whereby said
uninterrupted and then intermittent excitation is available at said
terminal means,
said control circuitry including first capacitor means, charging
and discharging circuit means connected with said first capacitor
means, operating means responsive to predetermined minimum and
maximum voltages developed across said first capacitor means for
causing the latter to charge via said circuit means when the
voltage across said first capacitor means falls to said minimum,
and to discharge via said circuit means when said voltage rises to
said maximum, and output means for delivering said output signal at
said first level during charging of the first capacitor means and
at said second level during discharge thereof, whereby said first
capacitor means, charging and discharging circuit means, and
operating means establish said duty cycle,
said control circuitry being provided with second capacitor means
of substantial capacitance, and means electrically connecting said
second capacitor means with said circuit means during charging
operation thereof but electrically isolating said second capacitor
means therefrom during discharging operation of said circuit means,
whereby upon said activation of the control circuitry both the
first and second capacitor means charge over a time duration
terminating when said voltage reaches said maximum, said time
duration defining said initial period occurring during said
monostable mode of operation.
3. The apparatus as claimed in claim 2 wherein said operating means
includes comparator means connected with said first and second
capacitor means for detecting the occurrence of said minimum and
maximum voltages.
4. The apparatus as claimed in claim 2, wherein said circuit means
has independent charging and discharging circuits operably coupled
with said first capacitor means, and means in said independent
circuits for varying the duration of said output signal at said
first and second levels in said astable mode, whereby said duty
cycle may be set at either less than or greater than 50
percent.
5. The apparatus as claimed in claim 4, wherein said charging
circuit is connected with said output means for applying said
output signal to said first and second capacitor means when the
signal is at said first level, there being means electrically
isolating said charging circuit from said output means when said
output signal is at its second level, whereby to maintain said
charging circuit completely independent from said discharging
circuit.
6. The apparatus as claimed in claim 1, wherein said operating
means includes comparator means connected with said first and
second capacitor means for detecting the occurrence of said minimum
and maximum voltages.
7. The apparatus as claimed in claim 1, wherein said circuit means
has independent charging and discharging circuits operably coupled
with said first capacitor means, and means in said independent
circuits for varying the duration of said control signal at said
first and second levels following said time period at the outset of
said program, whereby to control said pulse width and spacing at
said terminal means to provide a duty cycle either less than or
greater than 50 percent.
8. The apparatus as claimed in claim 7, wherein said charging
circuit is connected with said output means for applying said
control signal to said first and second capacitor means when the
signal is at said first level, there being means electrically
isolating said charging circuit from said output means when said
control signal is at its second level, whereby to maintain said
charging circuit completely independent from said discharging
circuit.
Description
This invention relates to driver apparatus for delivering
electrical excitation which is uninterrupted during an initial
period followed by intermittent delivery at a predetermined duty
cycle and, in particular, to a driver which is uniquely adapted for
solenoid control applications.
Solenoids are inherently characterized by a high ratio of pull-in
current to drop-out current due to air gap changes in the magnetic
circuit occurring with armature movement. Accordingly, once the
armature completes its stroke, the excitation requirements of the
solenoid coil decrease significantly, thereby making it possible to
realize a substantial power saving by reducing the drive. The
alternative is to select a solenoid having a continuous current
rating that is sufficiently high to permit operation at the pull-in
current level at all times. However, besides consuming considerably
more power, this requires that a more expensive, heavier-duty
solenoid coil be utilized than is really necessary for the
particular control application.
In an effort to take advantage of a reduced continuous current
rating, mechanical switches operated by the solenoid armatures have
been employed to switch the operating potential on a DC solenoid to
a lower level once the armature completes its stroke. Mechanical
latches have also been utilized. However, these approaches all
suffer from the disadvantage that mechanical parts subject to wear
and ultimate failure must be employed, thereby increasing the cost
of the solenoid device both initially and from the standpoint of
continuing servicing and maintenance. Furthermore, the problem is
enhanced in the case of armature-operated switches due to contact
wear inherent in switching an inductive load.
It is, therefore, an important object of the present invention to
provide a driver for solenoids that is devoid of mechanical parts
and yet capable of reducing the excitation to the solenoid coil
following pull-in, in order to minimize the required continuous
current rating of the solenoid.
As a corollary to the foregoing object, it is an important aim of
this invention to provide a driver as aforesaid which is not
subject to the disadvantages inherent in mechanical arrangements
for reducing the solenoid drive discussed hereinabove, and which
has a normal expected operating life exceeding that of the
solenoids it supplies.
It is another important object of this invention to provide a
driver as aforesaid which supplies uninterrupted excitation to the
solenoid during an initial period at the outset of a timing program
commencing with energization of the solenoid coil, followed by
intermittent delivery of excitation to the coil after pull-in is
completed.
Still another important object of the invention is to provide a
driver as aforesaid where the duty cycle after pull-in may be
varied over a wide range, including both less than and greater than
50 percent, in order to meet the holding current requirements of
the solenoid coil but be purposely limited to preclude unnecessary
power consumption.
Furthermore, it is an important object of the present invention to
provide driver apparatus, particularly for inductive loads, capable
of delivering electrical excitation which is uninterrupted during
an initial period followed by intermittent delivery at a
predetermined duty cycle, wherein the pulse width and spacing
during such duty cycle is variable over a wide range to accommodate
the particular application.
Additionally, it is an important object of this invention to
provide such apparatus wherein control circuitry is employed having
monostable and astable modes of operation, and wherein the control
circuitry upon activation initially operates in the monostable mode
followed by continuous operation in the astable mode.
Yet another important object of the invention is to provide such
apparatus having control circuitry as aforesaid wherein, in the
astable mode, the output of the circuitry is cycled between first
and second voltage levels in accordance with a desired pulse width
and spacing of the excitation to be supplied to the external
load.
A further and important object is to provide such control circuitry
incorporating capacitors with independent charging and discharging
circuits wherein the charge and discharge times are employed to
govern the duration of the monostable mode and the pulse width and
spacing of the output in the astable mode.
In the drawings:
FIG. 1 is an electrical schematic diagram illustrating the driver
apparatus of the present invention;
FIG. 2 is a timing diagram showing wave forms that illustrate the
operation of the apparatus in applications requiring greater than a
50 percent duty cycle following the initial period of
excitation;
FIG. 3 is a timing diagram similar to FIG. 2 but illustrating a
duty cycle of less than 50 percent;
FIG. 4 is a block diagram illustrating the functional sections of
the integrated circuit timer; and
FIG. 5 is an electrical schematic diagram showing the equivalent
circuit for the integrated circuit timer.
Referring initially to FIG. 1, the driver apparatus of the present
invention is shown connected to a solenoid 20 having an armature 22
mechanically coupled to a valve 24. In the application illustrated
in FIG. 1, the solenoid 20 is being utilized to control the opening
and closing of the valve 24 in conjunction with operation of any of
various types of equipment, such as the hydraulic valves associated
with heavy-duty construction equipment. In such applications the
solenoid 20 would be operated from battery potential (typically 12
volts) as represented by the +V notation. The solenoid coil is
connected to the supply terminals 26 of the driver, and the lattr
is activated by closing an on-off switch 28.
An integrated circuit timer 30 is employed in the preferred
embodiment of the driver illustrated herein, and has a number of
terminals designated by the numerals 1 through 8. Terminal 1 is a
ground connection as illustrated by the ground symbol. Terminal 2
is a trigger input, 3 is the output terminal of the timer 30,
terminal 4 is a reset, terminal 5 is a control voltage input,
terminal 6 is a threshold input, terminal 7 executes a discharge
function, and terminal 8 is connected to the supply voltage. The
particular integrated circuit illustrated herein is manufactured by
Signetics, a subsidiary of Corning Glass Works, of Sunnyvale,
Calif., and is currently available under the designation NE/SE 555.
Other equivalent integrated circuits may be employed or discrete
components may be substituted if desired. The nature of the
integrated circuit 30 will be discussed in detail hereinbelow with
reference to FIGS. 4 and 5.
In addition to the integrated circuit 30, the driver has a number
of additional components which cooperate with the circuit 30 to
execute the various control functions of the present invention. It
should be noted that the trigger input 2 and the threshold input 6
are interconnected, a capacitor 32 being connected between such
terminals and ground. A second capacitor 34 is in parallel with the
capacitor 32 through an isolation diode 36 poled to conduct
positive current in the direction of the capacitor 34. A reset
diode 38 extends from the upper plate of the capacitor 34 to a lead
40 which is at the level of the +V supply when switch 28 is
closed.
The capacitor 32 is charged and discharged through independent
circuits, the charging circuit being traceable from the output
terminal 3 to the capacitor 32 via a diode 42 and a
series-connected variable resistor 44. This also serves as the
charging circuit for the capacitor 34 through the diode 36. The
discharging circuit from capacitor 32 is through a variable
resistor 46 to the discharge terminal 7 of the integrated circuit
30. Terminals 4 and 8 are tied to the lead 40, and a noise bypass
capacitor 48 is connected between terminal 5 and ground.
The control circuitry comprising the integrated circuit 30 and its
associated external components delivers a control signal at the
output terminal 3 in the nature of a bilevel output which may be
considered either "high" or "low." These are analogous to logic
levels with the high level being at the positive supply voltage
(+V). A voltage divider consisting of resistors 50 and 52 delivers
the output signal to the base of an NPN switching transistor 54
having a grounded emitter. The collector of transistor 54 is
connected by a coupling resistor 56 to a Darlington amplifier 58
which serves as a switch between the +V lead 60 and the upper
supply terminal 26. A diode 62 is connected across the supply
terminals 26 and poled in opposition to the supply voltage to
provide transient suppression during switching of the solenoid
20.
Referring to FIG. 4, the integrated circuit timer 30 is revealed in
block diagram form. A voltage divider comprising three series
connected resistors R of equal value is connected between the
supply terminal 8 and ground. A first voltage comparator 64 has a
pair of inputs connected to the threshold input 6 and the junction
66 between the upper and center resistors R as they appear in the
illustration. A second voltage comparator 68 has a pair of inputs
respectively connected to the trigger input 2 and the junction
point 70 between the center and lower resistors R. The output 72 of
the comparator 68 is connected to the set input S of a flip-flop
74, the output 76 of the comparator 64 being connected to the reset
input R of the flip-flop 74.
An NPN transistor 78 is nonconductive when the capacitors 32 and 34
are charging, but is rendered conductive by the output 80 of the
flip-flop 74 to discharge the capacitor 32 during astable
operation, as will be discussed. The output stage 82 of the timer
30 is responsive to the flip-flop output 80 and delivers the
bilevel control signal at terminal 3.
FIG. 5 is an equivalent circuit of the timer 30 shown in block
diagram form in FIG. 4. The three resistors R forming the voltage
divider are also identified by the letter R in FIG. 5. When the
transistor 78 (connected between discharge terminal 7 and ground)
is nonconducting during charging of the capacitors 32 and 34, a
transistor 84 connected to output terminal 3 is conducting while a
second transistor 86 is in the nonconductive state. Both of the
transistors 84 and 86 are of the NPN type, the collector of
transistor 84 being connected to the supply terminal 8 while its
emitter is directly connected to the output terminal 3. The
transistor 86 has its emitter-collector circuit connected between
terminal 3 and ground with the emitter being grounded. Accordingly,
under the conditions just described with transistor 84 on and
transistor 86 off, output terminal 3 is at the high or +V voltage
level. Conversely, reversal of the states of these two transistors
places output terminal 3 at the low level (ground potential); at
this time the transistor 78 is conducting and the capacitor 32 is
discharging.
The control circuitry of the present invention has monostable and
astable modes of operation as illustrated by the timing diagrams in
FIGS. 2 and 3. Referring to FIG. 2, the wave form 88 represents the
output signal occurring at the output terminal 3 of timer 30. As
discussed above, the signal is either at the high level or the low
level indicated by +V and O respectively. The wave form 88 is also
representative of a timing program having an uninterrupted initial
period 90 followed by intermittent delivery of high level voltage
commencing on the positive excursion 92 of the first pulse 94 after
the long initial period 90. A series of three such pulses 94 is
illustrated, it being understood that the pulses 94 continue
indefinitely as long as the solenoid 20 is in operation.
A second wave form 96 is illustrated in FIG. 2 correlated in time
with the wave form 88. Wave form 96 represents the voltage at the
interconnected terminals 2 and 6 of the timer 30. Starting from O,
initial charging of the capacitors 32 and 34 occurs along a ramp 98
coinciding with the long initial period 90. The end of the ramp 98
is at a voltage level equal to 2/3of the supply voltage V.
Capacitor discharge is illustrated by the abrupt negative
excursions 100, each being followed by a short charging ramp 102.
The lower limit of each negative excursion 100 is at a voltage
level equal to 1/3 of the supply voltage.
The operation illustrated in FIG. 3 is similar to FIG. 2 except
that the duty cycle of the driver during the astable mode of
operation is less than 50 percent, whereas a duty cycle
significantly over 50 percent is illustrated in FIG. 2. The same
reference numerals are used with the addition of the a
notation.
OPERATION
The capacitance of capacitor 34 is much larger than that of
capacitor 32 in order to assure that the duration of the initial
period 90 will be sufficiently long to fulfill the pull-in current
requirements of the solenoid 20, irrespective of the value of the
resistor 44. Upon closure of the switch 28, the control circuitry
is activated and the parallel capacitors 32 and 34 begin charging
via the charging circuit from output terminal 3 through diode 42
and resistor 44. At this time, the transistor 78 (FIGS. 4 and 5) is
nonconductive and the output terminal 3 is at the high level.
Accordingly, there is no conduction of current through the resistor
46 to the discharge terminal 7.
Charging continues as shown by the ramp 98 (FIGS. 2 and 3) until
such time that the voltage developed across capacitors 32 and 34
reaches 2/3V. This is sensed by comparator 64 since one of its
inputs is connected to terminal 6 and its other input is connected
to the junction 66, the latter being maintained at the 2/3 V level
by the voltage divider action of the three resistors R. When a
voltage differential ceases to exist at the two inputs to the
comparator 64, it delivers an output at the high level to the reset
input R of the flip-flop 74. This causes the output 80 of the
flip-flop 74 to go from the low to the high level, thereby gating
the transistor 78 and commencing the discharge of capacitor 32. It
should be noted that the diode 36 precludes any significant
discharge of capacitor 34 so that the latter has little affect on
subsequent operation of the circuitry. Also at this time, the
output stage 82 of the integrated circuit timer 30 causes the
output terminal 3 to go to the low level (terminal 3 is effectively
shunted to ground by the conduction of transistor 86 shown in FIG.
5).
In FIG. 2 the discharge of the capacitor 32 is illustrated by the
ramp 100. Since the comparator 68 has its inputs connected to the
junction point 70 and terminal 2, it senses the absence of a
differential voltage at the time that the voltage across capacitor
32 falls to the 2/3 V level. Accordingly, the flip-flop 74 is set
at this time to again place transistor 78 in the nonconducting
state and cause the output at terminal 3 to go to the high level.
Charging now begins again, but this time only the capacitor 32 is
charged through the resistor 44. Charging is illustrated by the
shorter ramp 102 beginning in coincidence with the leading
excursion 92 of the first pulse 94.
The control signal depicted by the wave forms 88 in FIGS. 2 and 3
renders switching transistor 54 conductive when the control signal
is at the high level, and nonconductive when the control signal is
at the low level. Accordingly, transistor 54 and the succeeding
Darlington amplifier stage 58 constitute an electrically
responsive, bistate switch which controls delivery of supply
voltage to the upper supply terminal 26 in accordance with the
level of the control signal appearing at output terminal 3 of the
timer 30. During the initial period 90, excitation of the solenoid
coil was uninterrupted but now, as the circuitry begins its astable
mode of operation, power to the solenoid 20 is cycled on and off in
accordance with the frequency of the control signal. Both pulse
width and pulse spacing at the supply terminals 26 may be
independently controlled by the variable resistors 44 and 46 to
conform the duty cycle to the holding current requirements of the
solenoid. Thus, the required continuous current rating of the
solenoid is minimized and power is conserved.
During the monostable mode of operation when both of the capacitors
32 and 34 are charging, the time constant is a function of the
value of resistor 44 multiplied by the sum of the capacities of
capacitors 32 and 34. As mentioned hereinabove, the value of
capacitor 34 would be selected so as to be much greater than the
value of capacitor 32, thereby minimizing the effect of capacitor
32 on the period 90. During the subsequent astable mode of
operation, however, the time constant is a function of the product
of the ohmic value of resistor 44 and the capacitance of capacitor
32 alone. Then, during discharge, the time constant is a function
of the product of the ohmic value of resistor 46 and the
capacitance of capacitor 32. Accordingly, during the astable mode,
the charge time and the discharge time are entirely independent of
each other so that the duty cycle is theoretically variable over an
unlimited range. This enables the driver to accommodate a variety
of load requirements as exemplified by a comparison of the pulse
width and spacing in FIGS. 2 and 3. In FIG. 2 the duty cycle well
over 50 percent, while in FIG. 3 the duty cycle is less than 50
percent.
When the switch 28 is reopened, the diode 38 allows the larger
capacitor 34 to discharge so that the driver is rapidly reset in
readiness for a subsequent closure of switch 28. It should be
understood that, although the resistors 44 and 46 are illustrated
as variable, this is done to demonstrate the independent setting of
variables in the present invention, thus in practice both resistors
may be fixed at values determined by a particular application.
* * * * *