Method and apparatus for increasing energy output from capacitors

Abstract: In a method for increasing the energy output from a plurality of charged capacitors (C1, C2, C3), each of the capacitors is discharged, one after another, through a load. The capacitors are then coupled in series in successive, different combinations, each of which comprising a part or all of the capacitors and being discharged, one after another, through the load. An apparatus for increasing the energy output from a plurality of charged capacitors (C1, C2, C3) comprises a charging circuit (4), arranged to control the charging of the capacitors, and a controllable switching device (6), arranged to first connect each of the capacitors to a load for discharge of the capacitors, one after another. The switching device then couples the capacitors in series in successive, different combinations, each of which comprising a part or all of the capacitors, and connects them to the load for discharge of the series couplings, one after another.

Description: This invention relates to a method and an apparatus for increasing the energy output from a plurality of charged capacitors. Generation of pulses with an amplitude equal to twice the voltage of a charging battery when two or more capacitors connected in parallel are charged, the capacitors thereafter being connected in series to emit the pulse, is prior art and it is known from EP-A-0 445 800, GB-A-1 387 115 and GB-A-976 994. This technic has been used in e.g. pacemakers. The object of the present invention is to make possible the largest possible output of energy, stored in a plurality of capacitors, during the emission of a pulse which more closely resembles a square pulse than the pulse discharged from a single capacitor with the same capacitance as the sum of the capacitances of said plurality of capacitors. This object is achieved with a method and an apparatus according to claims 1 and 5 respectively. Each capacitor in said plurality of capacitors has a relatively brief time constant, so the corresponding discharge pulses would abate with unacceptable celerity. However, if according to the invention "new" capacitors are connected, one after another, and two or more capacitors in different series combinations are successively connected in series for the discharge when each capacitor has been used individually in this way, the voltage of the composite discharge pulse emitted this way is maintained, so a more or less square pulse is achieved. The capacitors can be connected in parallel or in series for the best possible output of energy. According to advantageous embodiments of the method according to the invention, every capacitor discharge is stopped when the voltage across the load drops to a predesignated level, preferably a constant level for all the discharges. Alternately, each capacitor discharge is allowed to continue for a predesignated period of time, preferably a constant period of time for all the discharges. The apparatus according to the invention comprises a charging circuitry for charging the capacitors to the desired voltage and a controllable switching device which connects the capacitors in different discharge configurations. The switching device can be controlled with varying degrees of intelligence, and the charging circuitry and the switching device are controlled by a control unit, preferably a microprocessor, according to one advantageous embodiment of the apparatus according to the invention. With the control unit the most advantageous combination of capacitors for the discharge can be calculated and set up with the switching device or the control unit, or the control unit can select among previously programmed capacitor coupling sequences which proved to be effective. According to another advantageous embodiment of the apparatus according to the invention, a measurement circuit is provided to measure the voltage across the capacitors and the series connections of the capacitors during the discharges and to stop the latter when the measured voltage drops to a predesignated level. The measurement circuit advantageously comprises A/D converters which send the measured voltage values to the control unit after each sub-discharge of the ensuing output pulse. If an unfavorable voltage is measured across any capacitor, polarity can e.g. be reversed under certain conditions, this capacitor can be excluded from the coupling configuration or possibly have its polarity reversed. One exemplified embodiment of the apparatus according to the invention as applied to a heart defibrillator will be described more in detail below referring to the accompanying drawings in which FIG. 1 shows a heart defibrillator, in block diagram form, with the apparatus according to the invention, and FIG. 2 shows, as an illustration of the function of the apparatus, an example of the output pulse from a defibrillation circuit equipped with the apparatus according to the invention. The heart defibrillator according to FIG. 1 comprises a defibrillator circuit 2 containing a control unit in the form of a microprocessor which, via its ports, controls charging circuitry 4 for the capacitors C1, C2, C3 and a switching device 6. Before the discharge operation for generating a defibrillation pulse starts, the capacitors C1, C2, C3 are charged from a battery by means of the charging circuitry 4. The intercoupling of the capacitors C1, C2, C3 in different configurations during the discharge operation is controlled by the microprocessor in the defibrillation circuit 2. The switches 8, 10, 12, 14, 16, 18 for intercoupling the capacitors C1, C2, C3 in different configurations are controlled by the switching device 6. However, the connections between the switching device 6 and the switches 8, 10, 12, 14, 16, 18 are not shown to eliminate needless clutter in the figure. The switchings in connection with the discharge operation will be explained below in greater detail in conjunction with FIG. 2. The voltage across each capacitor C1, C2, C3 is measured by the measurement circuit 20 after every discharge phase. The measurement circuit 20 can also continuously measure the voltage across the capacitor or the capacitors during the discharge operation in order to stop the prevailing discharge, via the microprocessor in the defibrillation circuit 2, when voltage across the capacitor or the capacitors drops to a predesignated level. The measurement circuit 20 can advantageously contain A/D converters which deliver values for measured voltage to the microprocessor of the defibrillation circuit 2, representing the capacitor voltage measured. If a voltage, unfavourable in the context, occurs across any capacitor, this capacitor can be left out in the envisaged coupling configuration. For example, the polarity of a given capacitor can be reversed. If viz. two capacitors charged to different voltages are connected in series and the same current flows in the circuit, the discharge will continue and current will be impelled by the capacitor with the higher voltage, so the polarity of the capacitor charged to the lower voltage is reversed. Thus, such a capacitor with reversed polarity will be bypassed in the envisaged coupling configuration or have its polarity reversed in the apparatus according to the invention. FIG. 2 shows the time course for the output voltage across the output contacts DEFIB1 and DEFIB2. In this example, we assumed that the capacitors C1, C2, C3 are of equal size. The time and voltage axes are subdivided in time and voltage units appropriate to the FIG. The capacitors C1, C2, C3 are connected in parallel to the charging circuit 4 before any discharge operation, so as to charge the capacitors C1, C2, C3 to the desired voltages. The discharge operation then begins, the switches 8, 10, 12, 14, 16, 18 being initially in the positions shown in FIG. 1 in which none of the switches 8, 10, 12, 14, 16, 18 conducts. In the first three phases of the discharge operation, the capacitors C1, C2, C3 are coupled, one after another, to the contacts DEFIB1 and DEFIB2 for discharging each of the capacitors C1, C2, C3 for a given period of time, i.e. 20 time units in FIG. 2, the voltages of the capacitors C1, C2, C3 then dropping to the same level. The capacitors C1 and C2 are then connected in series, and this series coupling is connected to the output contacts DEFIB1 and DEFIB2 for discharging C1 and C2, connected in series, for an additional 20 time units, from 60 time units to 80 time units in FIG. 2. Capacitor C3 is subsequently connected to the serially coupled C1 and C2, so the series coupling formed by all three capacitors C1, C2, C3 is coupled to the output contacts DEFIB1 and DEFIB2 for discharge for an additional 20 time units, from 80 time units to 100 time units. For the sake of comparison, the output pulse which would be supplied by a single capacitor with the same capacitance as the three capacitors C1, C2, C3 jointly is illustrated in FIG. 2. As shown in FIG. 2, an output pulse is achieved with the apparatus according to the invention which more closely resembles a square pulse than the discharge pulse from this single capacitor. With the invention, a biphasic pulse can also be achieved through phase reversal of the defibrillation pulse at a given time. In the example shown in FIG. 2, the phase of the pulse could therefore be reversed at the time 60 time units when the discharge of capacitors C1 and C2, connected in series, begins. The way in which the switches 8, 10, 12, 14, 16, 18 are to be set at different phases of the discharge operation, so the course shown in FIG. 2 is achieved, should be apparent from FIG. 1. FIG. 2 shows that each capacitor has a rather short time constant, so every individual capacitor would emit a pulse which decayed far too rapidly, but since new capacitors are coupled, one after another, and two or more capacitors connected in series are then discharged, output voltage rises, and the capacitors can be discharged to a greater degree. When the apparatus contains more than two capacitors, the intercoupling of these capacitors during the discharge operation can either be parallel or series, so the best possible utilization of energy is achieved. Here, as noted above, the voltage across a capacitor may be reversed. The capacitor polarity can then be reversed or the capacitor could simply not be connected. With appropriate programming of the microprocessor in the defibrillation circuit 2, the microprocessor can calculate the most favorable capacitor configuration or select among programmed coupling sequences previously found to be effective. One example of the apparatus according to the invention with three capacitors of equal size was described above. But both the number of capacitors and their size are obviously optional in the apparatus according to the invention. The apparatus is described above using an example applied to a heart defibrillator. However, the apparatus according to the invention can also be used for many kinds of other applications for which an increase in the energy output of capacitors and the best possible utilization of stored energy are desired.

Claims: A method for increasing the energy output from a plurality of charged capacitors (C1, C2, C3), characterized in that each of the capacitors is discharged, one after another, through a load, the capacitors then being coupled successively in series in different combinations, each of which comprises a part or all of the capacitors and which are discharged, one after another, through the load. The method of claim 1, characterized in that a number of the capacitors (C1, C2) in said plurality of capacitors is connected in series, after each of the capacitors (C1, C2, C3) has been discharged, whereafter this series connection is discharged through the load, whereupon one or more additional capacitor (C3) of said plurality of capacitors is connected in series to the existing series connection, and this new series connection of capacitors (C1, C2, C3) is discharged through the load, whereupon one or more additional capacitor of said plurality of capacitors is connected to the existing series connection, the operation being continued until all the capacitors, connected in series, in said plurality of capacitors have been discharged. The method of claim 1 or 2, characterized in that each discharge is stopped when the voltage across the load drops to a predesignated level, preferably a constant level for all the discharges. The method of any of claims 1 - 3, characterized in that each discharge is allowed to continue for a predesignated period of time, preferably a constant period of time for all the discharges. An apparatus for increasing the energy output from a plurality of charged capacitors (C1, C2, C3), a charging circuitry (4) being provided for controlling the charging of the capacitors, characterized in that a controllable switching device (6) is provided for first connecting each of the capacitors (C1, C2, C3) to a load for discharging the capacitors, one after another, and then coupling the capacitors in series in successively different combinations, each of which comprising a part or all of the capacitors, and connecting them to the load for discharging the series couplings, one after another. The apparatus of claim 5, characterized in that the controllable switching device (6) is arranged to couple a number of capacitors (C1, C2) in said plurality of capacitors in series and connect this series coupling to the load for discharge, after each of the capacitors (C1, C2, C3) has been connected to the load for discharge, and then couple one or more additional capacitors (C3) in said plurality of capacitors in series to the existing series coupling, and connect this new series coupling to the load for discharge etc. until all capacitors in said plurality of capacitors have been coupled in series and discharged through the load. The apparatus of claim 5 or 6, characterized in that the switching device (6) is arranged to couple, after discharge of each of the capacitors (C1, C2, C3), a series coupling of a first and a second capacitor (C1, C2) in said plurality of capacitors to the load for discharging the series coupling and then, after each discharge, connect a series coupling, augmented with an additional capacitor (C3), to the load for discharge until all the capacitors in said plurality of capacitors have been coupled in series and discharged through the load. The apparatus of any of claim 5 - 7, characterized in that a measurement circuit (20) is arranged to measure voltage across the capacitors (C1, C2, C3). The apparatus of any of claims 5 - 7, characterized in that a timer is provided for controlling the switching device (6), so every discharge lasts for a predesignated period of time. The apparatus of any of claims 5 - 9, characterized in that a control unit, preferably a microprocessor, is provided to control charging circuitry (4) and the switching device (6). The apparatus of claim 10, characterized in that the control unit is arranged to control the switching device (6) according to preprogrammed coupling sequences for the capacitors (C1, C2, C3). The apparatus of claim 10 or 11, characterized in that the measurement circuit (20) comprises an A/D converter which delivers the measured voltage values to the control unit. The apparatus of any of claims 5 - 12, characterized in that the charging circuitry (4) for charging the capacitors (C1, C2, C3) is provided to couple the capacitors (C1, C2, C3), connected in parallel, to a source of current or voltage. The apparatus of any of claims 5 - 13, characterized in that all the capacitors (C1, C2, C3) are of equal size. The apparatus of any of claims 5 - 14, characterized in that the control unit is part of a defibrillation circuit (2), and in that the discharge of the capacitors (C1, C2, C3) and the series couplings of capacitors form a heart defibrillation pulse.

Inventors: HEDBERG SVEN-ERIK, HEDBERG, SVEN-ERIK
Applicants: PACESETTER AB
Application year: 1993
Main classification: A61N1
IPC codes: H02M3, H02J1, H03K3, A61N1