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Claims  |
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I claim:
1. An apparatus for generating multiphasic defibrillation pulse waveforms
by selectively switching the continuous output of a single multilevel
source, comprising:
first and second output terminal means for electrical connection to the
heart;
a plurality of charge storage means forming a single multilevel source,
each said storage means storing an electrical charge to provide an output
potential;
low voltage power source means;
charging means connected to said plurality of charge storage means and said
low voltage power source means for charging each of said charge storage
means to a level suitable to cause defibrillation of the heart;
a plurality of switch means, each having control means operative to render
the switch means conductive in response to a control signal, one switch
means of said plurality being connected in circuit between a respective
one of each said charge storage means and each of said first and second
output terminal means for connecting the potential provided by the said
charge storage means to the respective terminal means when said switch
means is conductive sand disconnecting the potential provided by said
charge storage means form the respective terminal means when said switch
means is nonconductive; and
pulse generator means connected to said control means of said plurality of
switch means for applying control signals to said control means upon said
charge storage means reaching a predetermined level to thereby control the
conductive state of each of said plurality of switch means to sequentially
connect and disconnect said output potentials of said plurality of charge
storage means to and from said first and second output terminal means in
selected additive and subtractive combinations to generate a multiphasic
defibrillation pulse waveform for application to the heart.
2. The apparatus of claim 1 further comprising:
means responsive to the attainment by at least one of said plurality of
charge storage means of a predetermined level of charge
for disabling said charging means from further charging of said charge
storage means; and
means responsive to the attainment by said at least one of said plurality
of charge storage means of said predetermined level of charge for enabling
said pulse generator means to generate said multiphasic pulse waveform.
3. The apparatus of claim 2 wherein said means responsive to the attainment
of a predetermined level of charge comprises:
means for receiving signals indicative of said predetermined level of
charge;
means for producing from said signals a first scaled reference level;
means for detecting the valve of charge stored in at least one of said
charge storage means;
means for producing from the detected level of charge a second scaled level
indicative of said level of charge;
means for comparing said second scaled level with said first scaled
reference level; and
means responsive to said means for comparing for disabling said charging
means when aids second scaled level attains at least the level of said
first scaled reference level.
4. The apparatus of claim 1 wherein said charging means comprises:
charge generation means for generating an electrical charge during a charge
generation cycle;
charge coupling means for coupling said electrical charge to said charge
storage means for storing said electrical charge during a subsequent
charge coupling cycle; and
detector means for detecting the end of each charge coupling cycle and
initiating the next charge generation cycle.
5. The apparatus of claim 4 wherein said detector means comprises:
means for sensing the level of electrical charge generated during said
charge generation cycle;
means for detecting when said electrical charge has been stored by said
charge storage means; and
means responsive to said means for detecting for generating a signal
indicating the end of the charge coupling cycle when said means for
detecting detects that said electrical charge has been stored by said
charge storage means.
6. The apparatus of claim 5 including switch means connected in circuit
with said charge generation means, said switch means being responsive to
said signal generated by said detector means to conduct current through
said charge generation means thereby causing said charge generation means
to generate said electrical charge during said charge generation cycle,
and being responsive to the absence of said signal to prevent current from
flowing through said charge generation means thereby causing said charge
coupling means to couple the generated electrical charge to said charge
storage means during said charge coupling cycle.
7. The apparatus of claim 1 wherein said pulse generator means includes
a plurality of driver means for generating said control signals.
8. The apparatus of claim 7 wherein each of said plurality of driver means
is connected to the control means of a pair of said switch means connected
in circuit between at least one of said charge storage means and said
first sand second output terminals for simultaneously controlling the
conduction states of both switch means of said pair to connect and
disconnect the potential of said at least one charge storage means across
said first and second output terminals.
9. The apparatus of claim 8 wherein:
said plurality of switch means comprises two pairs of switch means;
said plurality of charge storage means comprises a first charge storage
means having a first output potential and a second charge storage means
having a second output potential;
a first switch means from each pair are connected in a first series
connection between said first output potential of said first charge
storage means and said second output potential of said second charge
storage means;
a second switch means from each pair are connected in a second series
connection parallel to the first series connection between said first
output potential of said first charge storage means and said second output
potential of said second charge storage means;
said first output terminal adapted for connection to a heart comprises the
junction of said first series connection between said first switch means
from each pair; and said second output terminal adapted for connection to
a heart comprises the junction of said second series connection between
said second switch means from each pair.
10. The apparatus of claim 8 including protection means connected to said
plurality of driver means disabling every other drive means of said
plurality from turning its corresponding pair of switch means to the
conductive state when any one of said driver means of said plurality is
already enabled to turn its corresponding pair of said switch means to the
conductive state.
11. A cardiac defibrillator, comprising:
first and second output terminal means for electrical connection to a
heart;
a plurality of charge storage means forming a single multilevel source of
waveforms, each storage means storing an electrical charge to provide an
output potential;
low voltage power source means;
charging means connected to said plurality of charge storage means and said
low voltage power source means for charging said charge storage means;
a plurality of switch means, each having control means operative to render
the switch means conductive in response to a control signal, one said
switch means of said plurality being connected in circuit between a
respective one of each said charge storage means and each of said first
and second output terminal means for connecting the potential provided by
the said charge storage means to the respective terminal means when said
switch means is conductive and disconnecting the potential provided by the
said charge storage means from the respective terminal means when said
switch means is non-conductive;
pulse generator means connected to said control means of said plurality of
switch means for applying control signals to said control means to thereby
connect and disconnect said output potentials of said plurality of charge
storage means to and from said first and second output terminal means to
and from said first and second output terminal means in selected additive
and subtractive combinations to generate a multiphasic defibrillation
pulse waveform for application to the heart;
means responsive to the onset of cardiac fibrillation for activating said
charging means and;
means responsive to the attainment by at least one of said charge storage
means of a predetermined level of charge sufficient to defibrillate the
heart for activating said pulse generator means.
12. The apparatus of claim 11 wherein said charging means comprises:
charge generation means for generating electrical charge during a charge
generation cycle;
charge coupling means for coupling said electrical charge to said charge
storage means during a subsequent charge coupling cycle; and
detector means for detecting the end of each charge coupling cycle and
initiating the next charge generation cycle.
13. The apparatus of claim 12 wherein said detector means comprises:
means for sensing the level of electrical charge generated during said
charge generation cycle;
means for detecting when said electrical charge has been stored by said
charge storage means; and
means responsive to said means for detecting for generating a signal
indicating the end of the charge coupling cycle when said means for
detecting detects that said electrical charge has been stored by said
charge storage means.
14. The apparatus of claim 13 including switch means connected in circuit
with said charge generation means, said switch means being responsive to
said signal generated by said detector means to conduct current through
said charge generation means thereby causing said charge generation means
to generate said electrical charge during said charge generation cycle,
and being responsive to the absence of said signal to prevent current from
flowing through said charge generation means thereby causing said charge
coupling means to couple the generated electrical charge to said charge
storage means during said charge coupling cycle.
15. The defibrillator of claim 11 wherein said pulse generator means
includes
a plurality of driver means for generating said control signals.
16. The defibrillator of claim 15 wherein each of said plurality of driver
means is connected to the control means of a pair of said switch means
connected in circuit between at least one of said charge storage means and
said first and second output terminals for simultaneously controlling the
conduction states of both switch means of said pair to connect and
disconnect the potential of said at least one charge storage means across
said first and second output terminals.
17. The defibrillator of claim 16 wherein:
said plurality of switch means comprises two pairs of switch means;
said plurality of charge storage means comprises a first charge storage
means having a first output potential and a second charge storage means
having a second output potential;
a first switch means from each pair are connected in a first series
connection between said first output potential of said first charge
storage means and said second output potential of said second charge
storage means;
a second switch means from each pair are connected in a second series
connection parallel to the first series connection between said first
output potential of said first charge storage means and said second output
potential of said second charge storage means; said first output terminal
adapted for connection to a heart comprises the junction of said first
series connection between said first switch means from each pair; and said
second output terminal adapted for connection to a heart comprises the
junction of said second series connection between said second switch means
from each pair.
18. The defibrillator of claim 17 including protection means connected to
said plurality of driver means and responsive to said control signals for
automatically disabling every other driver means of said plurality from
turning its corresponding pair of switch means to the conductive state
when any one of said driver means of said plurality is already enabled to
turn its corresponding pair of switch means to the conductive state.
19. An electrical stimulator apparatus, comprising:
first and second output terminal means for electrical connection to tissue
to be stimulated;
a plurality of charge storage means forming a single multilevel source,
each said storage means storing an electrical charge to provide an output
potential;
low voltage power source means;
charging means connected to said plurality of charge storage means and said
low voltage power source means for charging said charge storage means;
a plurality of switch means, each having control means operative to render
the switch means conductive in response to a control signal, one switch
means of said plurality being connected in circuit between a respective
one of said charge storage means and each of said first and second output
terminal means for connecting the potential provided by the said charge
storage means to the respective terminal means when said switch means is
conductive and disconnecting the potential provided by the said charge
storage means from the respective terminal means when said switch means is
non-conductive;
pulse generator means connected to said control means of said plurality of
switch means for applying control signals to said control means to thereby
connect and disconnect said output potentials of said plurality of charge
storage means to and from said first and second output terminal means in
selected additive and subtractive combinations to generate a multiphasic
pulse waveform for application to said tissue to be stimulated and
lead means connected between said first and second output terminal means
and the tissue to be stimulated.
20. The stimulator apparatus of claim 19, including:
means responsive to a predetermined physiological condition for enabling
said charging means to charge said charge storage means; and
means responsive to the attainment by at least one of said charge storage
means of a predetermined level of charge for enabling said pulse generator
means to generate said multiphasic pulse waveform .
21. A cardiac defibrillator, comprising:
a single source having a plurality of storage means for storing multilevel
electrical charges; means responsive to onset of fibrillation for
initiating charging of said storing means;
means for detecting the level of charge stored by said storing means to
interrupt said charge upon attainment of a preselected level of stored
charge; and
means responsive to attainment of said preselected level for sequentially
discharging said storing means with successive alternations of polarity
over selected time intervals to generate a multiphasic pulse waveform
having at least two successive electrical pulses of predetermined
magnitude, duration, and opposite polarity sequence, with energy content
sufficient for defibrillation, for delivery to the patient's heart.
22. The defibrillator of claim 21, wherein said discharging means includes
means for selecting the polarity with which said storing means is first
discharged upon attainment of said preselected level, to establish the
sequence of alternating polarity of the pulses in said waveform.
23. The defibrillator of claim 21, further including
means for setting said time intervals to establish the duration of each
pulse in said waveform.
24. The defibrillator of claim 21, further including
means for setting said preselected level of charge to establish the initial
magnitude of the first pulse in said waveform.
25. The defibrillator of claim 24, further including
means for setting said time intervals and the separation thereof, to
establish the duration of each pulse, and the initial magnitude of each
pulse following the first pulse, in said waveform.
26. The defibrillator of claim 21, wherein said charging means includes
means for cyclically delivering packets of electrical charge to said
storing means, each packet having a predetermined magnitude, until
attainment of said preselected level.
27. The defibrillator of claim 21, further including
conductive lead means for connection at one end thereof to said discharging
means and including electrode means at the other end thereof for making
electrically stimulating relationship to the patient's heart, to deliver
said waveform to the heart.
28. The defibrillator of claim 21, wherein
said storing means includes a pair of series-connected high-voltage
charge-storing capacitors,
said charging means includes means for cyclically delivering electrical
charge in packets, each of predetermined magnitude, to the charge-storing
capacitors until said preselected level of charge is attained, and
said discharging means includes means for generating said waveform by
sequential discharge of the capacitors to provide the sequence of pulses
of successively opposite polarity.
29. The defibrillator of claim 28, wherein
said generating means partially discharges the charge stored on both
capacitors in first one polarity and then the opposite polarity.
30. The defibrillator of claim 28, wherein
said generating means partially discharges the charge stored on only one of
said capacitors in one polarity and then discharges the charge stored on
the other capacitor and the remaining charge stored on said one capacitor
in the opposite polarity. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention disclosed herein relates generally to the field of heart
defibrillator equipment. More specifically, the present invention relates
to a special defibrillator apparatus which is suitable for use in
implantable, automatic cardioversion systems, and which can generate
particularly effective and beneficial high-voltage multiphasic
defibrillation waveforms.
2. Description of the Prior Art
Ventricular fibrillation is almost always fatal unless promptly arrested.
It has long been known that the application of a high energy pulse to the
heart is often particularly effective in arresting this otherwise fatal
condition and in restoring the synchronous operation of the heart muscles.
Automatic, implantable fibrillation sensors and defibrillation pulse
generators are known in the art. See, for example, U.S. Pat. Nos.
3,614,954 and 3,614,955 to Mirowski et al., U.S. Pat. No. 4,254,775 to
Langer, and U.S. Pat. No. 4,384,585 to Zipes. Such defibrillators, in
order to be feasible, must occupy a minimal amount of space, be reliable
in operation, and make efficient use of a depletable energy source.
It has been common for such prior art implantable defibrillators to
generate unipolar type high-energy defibrillation pulses. See, for
example, U.S. patent No. to Langer, U.S. Pat. No. Re. 30,387 to Denniston
et al., U.S. Pat. No. Re. 30,372 to Mirowski et al., and U.S. Pat. No.
4,210,149 to Heilman et al. However, the use of unipolar pulses has been
known to produce certain undesirable side effects including damage to the
heart tissue near the electrode sites, induction of certain post-shock
arrhythmias, and changes in the S-T segment. Moreover, under certain
circumstances, such pulses are not effective to arrest ventricular
fibrillation.
Recent medical research has shown that many of the problems associated with
unipolar cardioverting pulses are alleviated or eliminated entirely when
multiphasic cardioverting pulse trains are employed and that certain
benefits are also obtained. For instance, it has been found that certain
beneficial post-shock effects are imparted to the defibrillated heart by
the trailing pulse of a three phase defibrillation waveform and that the
effect vary with the level of energy imparted to the heart by this pulse.
In addition, it has been found that the success rate in arresting
ventricular fibrillation using three phase pulse waveforms is
significantly greater than with unipolar pulses. See, for example,
Schuder, Defibrillation of 100 kg Calves With Asymmetrical, Bidirectional,
Rectangular Pulses, Cardiovascular Research 419-426 (1984), and Jones,
Decreased Defibrillator-Induced Dysfunction With Biphasic Rectangular
Waveforms, Am. J. Physiol. 247 (Heart Circ. Physiol. 16): H792-H796
(1984). Of course, many multiphasic waveform variations are possible and
research is continuing in this area to discover others which may provide
additional benefits and advantages in cardioverting and other
applications.
A number of apparatuses for generating various forms of biphasic signals
for pacing or defibrillation applications are known. One group of known
apparatuses are manually-operated, electromechanical defibrillation pulse
generators. These are not intended for and are totally unsuitable for use
in automatic, implantable defibrillation systems, due to their size,
mechanical nature, and high power requirements. See, for example, the
biphasic defibrillation pulse generators described in U.S. Pat. Nos.
3,093,136 to Lohr, 3,241,555 to Caywod et al., and 3,359,984 to Daniher et
al.
Another group of known apparatuses are biphasic pacing pulse generators
such as those described in U.S. Pat. Nos. 3,924,641 to Weiss, 4,402,322 to
Duggan, 3,563,247 to Bowers, and 3,946,745 to Hsiang-Lai et al. These
known apparatuses have solved some of the problems of the
electromechanical biphasic defibrillation pulse generators, but are not
intended for and are not suitable for efficiently generating and applying
to the heart the high-voltage pulses necessary to arrest ventricular
fibrillation. In addition, the known pacing pulse generators lack the
flexibility to generate the variety of multiphasic waveforms which medical
research has recently shown to be advantageous in cardioversion
applications, and to generate additional waveforms which continuing
research may in the future discover to be beneficial. Moreover, these
known generators provide no protection to the patient from internal
malfunctions.
Accordingly, it is an object of the present invention to provide a highly
energy efficient multiphasic pulse generator suitable for use in
implantable automatic defibrillators.
It is another object to provide such a generator that is simple but
flexible in its design and application and that can generate a variety of
multiphasic waveforms.
It is still another object to provide a multiphasic defibrillation pulse
generator that provides improved operational stability and accuracy
independent of the magnitude of the pulses to be applied to the heart.
It is a further object to provide a multiphasic pulse generator that
provides safeguards to the patient against internal malfunctions.
SUMMARY OF THE INVENTION
The above objects and attendant advantages are achieved by providing an
apparatus which generates multiphasic defibrillation pulse waveforms
having selected parameters of magnitude, polarity, and duration. The
apparatus includes a charging circuit connected to a charge-storing
circuit which provides at least three different output potentials. The
charging circuit charges the chargestoring circuit to a selected charge
level in response to a control signal indicative of fibrillation. An
electrical conduction device conducts the output potentials to a heart.
When the charge storing circuit is charged to a selected charge level, a
multiphasic pulse generator selectively and sequentially connects and
disconnects the conduction device and the output potentials to deliver to
the heart a multiphasic defibrillation waveform having pulses with
selected duration, magnitude, and polarity parameters.
The novel elements believed to be characteristic of the present invention
are set forth in the appended claims. The invention itself, together with
additional objects and attendant advantages, will best be understood by
reference to the following detailed description, which, when taken in
conjunction with the accompanying drawings, describes a presently
preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
An exemplary illustration of an apparatus for generating a multiphasic
defibrillation pulse waveform comprising a presently preferred embodiment
of the invention is contained in the appended drawings in which:
FIG. 1 is a general block diagram of the apparatus for generating a
multiphasic defibrillation pulse shown with a heart;
FIG. 2 is block diagram of the charging circuit block of FIG. 1;
FIG. 3 is a schematic diagram of the charging circuit block diagram of FIG.
2;
FIG. 4 is a block diagram of the voltage level regulation block component
of FIG. 1;
FIG. 5 is a block diagram of the multiphasic pulse generator block of FIG.
1 shown with a heart;
FIG. 6 is a schematic diagram of the FET driver circuits S1-S4 shown in
FIG. 5;
FIG. 7 is a schematic diagram of the nonoverlap protection circuit shown in
FIG. 5;
FIG. 8a is a timing diagram showing the relative timing -of the oscillator
output, one-shot output, and charge-control signal of the circuit of FIG.
3;
FIG. 8b is a timing diagram showing the relative timing of the oscillator
output, the one-shot output, and the voltage E.sub.L at the drain of the
power FET 24 in the circuit of FIG. 3; and
FIG. 8c is a diagram illustrating a typical multiphasic defibrillation
pulse waveform for delivery to a heart.
DETAILED DESCRIPTION OF A PRESENTLY PREFERRED EMBODIMENT
FIG. 1 shows a block diagram of a multiphasic defibrillation pulse
generator apparatus comprising a presently preferred embodiment of the
invention. The apparatus comprises a charging circuit 10, a multiphasic
pulse generator 11, and first and second high-voltage charge-storing
series capacitors 12,13 positioned between the charging circuit 10 and
multiphasic pulse generator 11 in parallel therewith and electrically
interconnecting the two. The series connection of the charge-storing
capacitors 12,13 establishes three terminals, A, B, and C, with terminal B
being a common terminal, and each of the terminals having a different
potential when the charge-storing capacitors 12,13 are charged. The
multiphasic pulse generator 11 in turn electrically connects to the heart
14 via electrically conductive output and return leads 15,16. Leads 15,16
typically have first and second conductive patches 17,18, or other
conductive connectors attached to their respective free ends for making
electrical connection to the heart 14 in a manner and location known to
those skilled in the art. A voltage level detector 19 is electrically
connected across the second charge-storing series capacitor 13, and to the
charging circuit 10. A controller 9 supplies control signals over control
lines 20 to the charging circuit 10 and multiphasic pulse generator 11 to
control their operation.
The first and second charge-storing capacitors 12,13 are suitably 350
microfarad aluminum electrolyte type capacitors such s those manufactured
by Rubycon. The controller may be any conventional microprocessor or other
digital or analog controller suitable for use in automatic, implantable
devices. An example of such controller can be found in U.S. Pat. Nos.
4,390,022 and 4,404,972.
The construction and use of such controllers is well known to those skilled
in the art and a description herein is not necessary to an understanding
of the present invention.
The controller 9 senses when the heart 14 enters a state of fibrillation
and in response generates a "charge enable" control signal. Many ways for
sensing and determining fibrillation are known to those skilled in the
art, and the controller suitably determines the condition of fibrillation
in any such known manner. The "charge enable" signal is conducted by the
control lines 20 to the charging circuit 10. In response, the charging
circuit 10 very quickly (typically 6-7 seconds) charges the first and
second charge-storing capacitors 12,13 to first and second preselected
voltages. In the presently preferred embodiment, the capacitors 12,13 are
simultaneously charged to equal voltages. The voltage level detector 19
determines when the first and second charge-storing capacitors 12,13 are
charged to the preselected voltage levels and generates a "charge disable"
control signal which is transmitted over line 8 both to the charging
circuit 10 and to the controller 9. The controller then generates a series
of control signals which are conducted by the control lines 20 to the
multiphasic pulse generator 11. The biphasic pulse 11 is responsive to
these control signals to electrically switch the output and return leads
15,16 into and out of contact with the terminals A, B, C of the
charge-storing capacitors 12,13, thereby establishing selected discharge
paths for the capacitors 12,13 through the heart 14. The polarities,
durations, and magnitudes of the discharges are determined by the control
signals.
After a first multiphasic defibrillation pulse waveform is delivered to the
heart 14, the controller may again sense the heart's condition and
initiate additional charging and defibrillation, if necessary. Preferably,
the controller senses the electrical activity of the heart 14, and stores
the number of defibrillation attempts. When no electrical activity is
sensed, or when a predetermined number of unsuccessful defibrillation
attempts have been made, the controller preferably does not initiate
further defibrillation attempts.
As shown in FIG. 2, the charging circuit preferably has a free-running
oscillator 21, the output terminal of which is connected to the trigger
terminal of a one-shot 22. The output terminal of the one-shot 22 in turn
connects to the input of a driver 23, the output of which controls the
gate of an N-channel power FET 24. The source of the power FET 24 is
connected to ground while the drain connects to one end of a first primary
coil 26 which comprises part of a charging transformer 25. The first
primary coil 26 connects at its opposite end to one end of a second
primary coil 27. The opposite end of the second primary coil 27 connects
to the anode of a diode 32, the cathode of which in turn connects to one
terminal of a power switch 33. A capacitor 34 is also preferably connected
between the cathode of the diode 32 and ground to inhibit power spikes.
The other terminal of the power switch 33 connects to the positive supply
input terminals of the oscillator, one shot, and driver 21, 22, and 23
respectively. A control line 20a labelled "charge," connects the
controller 9 through the voltage level detector 19 to the enable terminal
of the one-shot 22, and to the on/off terminal of the power switch 33.
The secondary of the charging transformer 25 contains first and second
secondary coils 28,29. The first secondary coil 28 connects at one end to
the anode of a first diode 30a. The cathode terminal of the first diode
30a in turn connects to terminal A of the first charge-storing capacitor
12. At its opposite end, the first secondary coil 28 connects to the
common terminal B of the first and second series charge-storing capacitors
12,13. The second secondary coil 29 connects at one end to the anode of a
second diode 30b, the cathode of which connects to the common terminal B
of the first and second series charge-storing capacitors 12,13. At its
opposite end, the second secondary coil 29 connects to terminal C of the
second charge-storing capacitor 13.
Also connected to the drain of the power FET 24 is the input of a "flyback"
or charge coupling cycle termination detector 31. The output of the
"flyback" termination detector 31 is connected to the trigger terminal of
the oscillator 21.
A positive voltage supply 28 is tapped between the first and second primary
coils 26,27 of the charging transformer 25. The positive voltage supply 28
is preferably capable of providing nine (9) volts DC over a long period of
time. In the presently preferred embodiment, three lithium cells stacked
in series have been found suitable for this purpose.
As illustrated in the schematic diagram of FIG. 3, an Intersil ICM-7556
dual general purpose timer 35 or equivalent may be used to implement the
oscillator 21 and oneshot 22. The ICM-7556 is a CMOS device and is
preferred over bipolar equivalents for its very low operating current
requirement as compared to equivalent bipolar devices. Additionally, the
ICM-7556, being a dual device, provides both space and component savings.
In the presently preferred embodiment, pins 1-6 of the ICM-7556 are used to
implement the one-shot 22. A resistor 36 is connected at one end to the
supply voltage pin (pin 14) and at the other end to a capacitor 37, and to
the one-shot discharge and threshold pins (pins 1,2) in parallel. The
opposite end of the capacitor 37 is connected to ground. The RC time
constant established by the resistor 36 and capacitor 37 controls the
duration of the one-shot output pulse. It has been found that the best
efficiency in charging the first and second series capacitors 12,13 is
obtained when the duration of the output pulse is approximately eight (8)
microseconds, which value is preferred for that reason. This value of
duration is preferably obtained by choosing a value for the resistor 36 of
approximately 80K ohms, and for the capacitor of approximately 100
picofarads. Although other combinations of resistance and capacitance
would also provide the appropriate duration value, it is preferable to use
high resistance and low capacitance values to minimize the current drain
on the positive voltage source 28.
The one-shot 22 is enabled by the application of a positive signal to the
one-shot reset pin (pin 4). Such a signal is supplied by the controller
(not shown) through the voltage level detector 19 by way of the "charge"
control line 20a. A series 10K ohm resistor 38 preferably limits the
current flow to the one-shot reset pin (pin 4). A positive pulse having
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