IMPLANTABLE MEDICAL DEVICE COMPRISING A DC-DC CONVERTER

Abstract

The present invention relates to a step-up converter with a plurality of levels, in particular for use in an implantable medical device, comprising a transformer (11) comprising a single primary winding and a single secondary winding; a primary circuit (6) comprising the single primary winding; and a secondary circuit (7) comprising the single secondary winding and a plurality of step-up levels, each of the step-up levels comprising a first diode (4a, 4b, 4c, 4d, 4e, 4f) and a second diode (10a, 10b, 10c, 10d, 10e, 10f) and a first capacitor (9a, 9b, 9c, 9d, 9e, 9f) and a second capacitor (3a, 3b, 3c, 3d, 3e, 3f), wherein the first capacitors (9a, 9b, 9c, 9d, 9e, 9f) of the plurality of step-up levels are connected in series or in parallel with one another. The present invention also relates to an implantable medical device comprising the step-up converter with a plurality of levels mentioned above, and a method for using the step-up converter with a plurality of levels or the implantable device mentioned above.

Claims

1. Step-up converter with a plurality of levels for use in an implantable medical device, comprising a transformer (11) comprising a single primary winding (11a) and a single secondary winding (11b); a primary circuit (6) comprising the single primary winding; and a secondary circuit (7) comprising the single secondary winding and a plurality of step-up levels, at least one step-up level, in particular each level, comprising a first diode (4a, 4b, 4c, 4d, 4e, 4f) and a second diode (10a, 10b, 10c, 10d, 10e, 10d), a first capacitor (9a, 9b, 9c, 9d, 9e, 9f) and a second capacitor (3a, 3b, 3c, 3d, 3e, 3f).

2. Step-up converter with a plurality of levels according to claim 1, wherein the primary circuit (6) comprises a primary power source (1) connected in series to the first winding (11a) and a switching device (2) connected in series with the first winding (11a).

3. Step-up converter with a plurality of levels according to claim 1 or claim 2, wherein the primary circuit (6) additionally comprises an inductor (15).

4. Step-up converter with a plurality of levels according to any one of claims 1 to 3, wherein a step-up level comprises only one capacitor (3e) and only one diode (4e), one terminal of the capacitor (3e) being directly connected to one terminal of the single secondary winding (11b), and the diode (4e) linking the other terminal of the capacitor (3e) to the other terminal of the single secondary winding (11b).

5. Step-up converter with a plurality of levels according to any one of the preceding claims, wherein in at least one step-up level, in particular in each of the step-up levels, the anode of a first diode (4a, 4b, 4c, 4d, 4e, 4f) is connected to one of the terminals of the first capacitor (9a, 9b, 9c, 9d, 9e, 9f) and to the cathode of the second diode (10a, 10b, 10c, 10d, 10e, 10f), one of the terminals of the second capacitor (3a, 3b, 3c, 3d, 3e, 3f) is connected to the cathode of the first diode (4a, 4b, 4c, 4d, 4e, 4f), and the other terminal of the second capacitor (3a, 3b, 3c, 3d, 3e, 3f) is connected to the anode of the second diode (10a, 10b, 10c, 10d, 10e, 10f).

6. Step-up converter with a plurality of levels according to any one of the preceding claims, wherein the second capacitors (3a, 3b, 3c, 3d, 3e, 3f) of each of the plurality of step-up levels are connected in series with each other.

7. Step-up converter with a plurality of levels according to any one of the preceding claims 2 to 6, wherein the step-up converter with a plurality of levels is configured to step up a voltage of the primary power source (1) in the range of 1 V to 9 V to an output voltage provided by the second capacitors (3a, 3b, 3c, 3d, 3e, 3f) of the step-up levels in the range of 10 V to 100 V or in the range 100 V to 2000 V.

8. Step-up converter with a plurality of levels according to any one of the preceding claims, wherein the turn ratio of the first winding (11a) np to the single secondary winding (11b) ns, is ns/np?2.

9. Step-up converter with a plurality of levels according to any one of the preceding claims, wherein the primary circuit (6) and the secondary circuit (7) are galvanically isolated from each other.

10. Step-up converter with a plurality of levels according to any one of claims 2 to 9, wherein the switching device (2) comprises a transistor device, in particular, a MOSFET device.

11. Step-up converter with a plurality of levels according to any one of claims 2 to 10, wherein the primary circuit (6) comprises a capacitor (12) connected in parallel to the primary power source (1).

12. Step-up converter with a plurality of levels according to any one of the preceding claims, wherein the primary circuit (6) comprises a first sensing means (13) for sensing a current flowing in the first winding and a second means (14) for sensing oscillations at the terminals of the switching device (2).

13. Step-up converter with a plurality of levels according to any one of the preceding claims, moreover comprising another transformer comprising another primary winding, in particular, another single primary winding, and another secondary winding, in particular, another single secondary winding.

14. Step-up converter with a plurality of levels according to any one of the preceding claims wherein the first capacitors (9a, 9b, 9c, 9d) of the step-up levels of the secondary circuit (7) are connected in parallel or in series with each other.

15. Step-up converter with a plurality of levels for use in an implantable medical device, comprising a transformer (11) comprising a single primary winding (11a) and at least two secondary windings (11b and 11c); a primary circuit (6) comprising the single primary winding, and a secondary circuit (7) comprising the secondary windings and a plurality of step-up levels, each of the step-up levels being associated with one of the secondary windings, a step-up level, in particular each step-up level, comprising one first diode (4a, 4b, 4c, 4d, 4e) and one second diode (10a, 10b, 10c, 10d, 10e, 10f) and one first capacitor (9a, 9b, 9c, 9d, 9e, 9f) and one second capacitor (3a, 3b, 3c, 3d, 3e, 3f).

16. Step-up converter with a plurality of levels according to claim 15, wherein in a step-up level, in particular in each of the step-up levels, the anode of the first diode (4a, 4b, 4c, 4d, 4e, 4f) is connected to one of the terminals of the first capacitor (9a, 9b, 9c, 9d, 9e, 9f) and to the cathode of the second diode (10a, 10b, 10c, 10d, 10e, 10f), one of the terminals of the second capacitor (3a, 3b, 3c, 3d, 3e, 3f) is connected to the cathode of the first diode (4a, 4b, 4c, 4d, 4e, 4f), and the other terminal of the second capacitor (3a, 3b, 3c, 3d, 3e, 3f) is connected to the anode of the second diode (10a, 10b, 10c, 10d, 10e, 10f).

17. Step-up converter with a plurality of levels according to any one of the preceding claim 15 or 16, wherein the second capacitors (3a, 3b, 3c, 3d, 3e, 3f) of each of the plurality of step-up levels are connected in series with each other and/or the first capacitors (9a, 9b, 9c, 9d) are connected in series or parallel with each other.

18. Step-up converter with a plurality of levels according to any one of claims 15 to 17, wherein a step-up level comprises only one capacitor and only one diode, the capacitor being directly connected to one terminal of the one of the secondary windings (11b or 11c), and the diode linking the other terminal of the capacitor to the other terminal of the same secondary winding (11b or 11c).

19. Implantable medical device comprising the step-up converter with a plurality of levels according to any one of the preceding claims.

20. Implantable medical device according to claim 19, wherein the implantable medical device consists of or comprises an implantable defibrillator (21), in particular, a subcutaneous implantable defibrillator.

21. Method for using the step-up converter with a plurality of levels according to any one of claims 2 to 18 or the implantable device according to claim 19 or 20, comprising the steps of: a) closure of the switching device of the step-up converter with a plurality of levels for a first period of time such that the first winding stores energy according to a peak value of an electric current flowing in the primary circuit and such that the first capacitors are charged to voltages of the second capacitors; b) opening the switching device of the step-up converter with a plurality of levels during a second period of time, in particular, immediately after the first period of time, so that energy is transferred from the first capacitors and secondary winding(s) to the second capacitors; and repeat steps a) and b) until a predefined output voltage can be supplied by the second capacitors.

22. Method according to claim 21, wherein the duration of the first period increases, in particular in a progressive manner, over all or part of the iterations of steps a) and b).

23. Method according to claim 21 or 22, wherein the maximum of the current (Ip) in the primary circuit (6) increases, in particular in a progressive manner, over all or part of the iterations of steps a) and b).

Description

[0038] Additional features and advantages of the present invention will be described with reference to the drawings. In the description, reference is made to the appended figures which are intended to illustrate preferred embodiments of the invention. It is understood that such embodiments do not represent the full scope of the invention.

[0039] FIG. 1a represents a first example of a flyback converter of an implantable medical device according to the state of the art.

[0040] FIG. 1b represents a second example of a flyback converter of an implantable medical device according to the state of the art.

[0041] FIG. 2a represents a step-up converter with a plurality of levels of an implantable medical device comprising a transformer and step-up levels according to a first embodiment of the present invention.

[0042] FIG. 2b shows a step-up converter with a plurality of levels of an implantable medical device comprising a transformer and step-up levels according to a variant of the first embodiment of the present invention.

[0043] FIG. 2c shows the signal at the gate of the MOSFET as a function of time.

[0044] FIG. 2d shows the current Ip in the first circuit 6 as a function of time.

[0045] FIG. 3 shows a step-up converter with a plurality of levels of an implantable medical device comprising a transformer and step-up levels according to a second embodiment of the present invention.

[0046] FIG. 4 represents a step-up converter with a plurality of levels of an implantable medical device comprising a transformer and step-up levels according to a third embodiment of the present invention.

[0047] FIG. 5 represents a step-up converter with a plurality of levels of an implantable medical device comprising a transformer with two secondary windings and step-up levels according to a fourth embodiment of the present invention.

[0048] FIG. 6 represents a step-up converter with a plurality of levels of an implantable medical device comprising two transformers according to a fifth embodiment of the present invention.

[0049] FIG. 7 represents an implantable defibrillator comprising a step-up converter with a plurality of levels according to one embodiment of the present invention.

[0050] The present invention relates to a step-up converter with a plurality of levels, or even a multilevel flyback converter for stepping up a DC voltage supplied by a primary power source of an implantable medical device. According to one embodiment, the step-up converter with a plurality of levels comprises a transformer comprising a single primary winding and a single secondary winding and a plurality of step-up levels.

[0051] According to another embodiment, the step-up converter with a plurality of levels comprises a transformer comprising one single primary winding and at least two secondary windings, in particular two secondary windings, and a plurality of step-up levels.

[0052] An example of one embodiment of a step-up converter with a plurality of levels is shown in FIG. 2a. The step-up converter with a plurality of levels comprises a primary circuit 6, at low voltage, and a secondary circuit 7, at high voltage, which are galvanically isolated from each other. The primary circuit 6 comprises a primary power source 1, in particular, a DC source, for example, a battery or a plurality of batteries in series. The battery may be, for example, a lithium-manganese dioxide battery or a lithium-carbon monofluoride battery or a lithium-silver vanadium oxide battery and may provide a battery voltage VA in the range of 3 V, 6 V or 9 V. Moreover, the primary circuit 6 comprises a switching device 2, for example, comprising a transistor device, in particular, a MOSFET transistor.

[0053] The step-up converter with a plurality of levels comprises a transformer 11. The transformer 11 comprises a single primary winding 11a with np turns or coil as part of the primary circuit 6 and a single secondary winding 11b with ns turns or coil as part of the secondary circuit 7. The ratio ns/np is preferably greater than or equal to 2. The secondary circuit 7 comprises several step-up levels, the number of which levels is not restricted. The step-up levels comprise a first plurality of capacitors 9a, 9b, 9c, 9d, also referred to as coupling capacitors, and a second plurality of capacitors 3a, 3b, 3c, 3d, also referred to as surge capacitors. Moreover, the step-up levels of the secondary circuit 7 comprise a first plurality of diodes 4a, 4b, 4c, 4d and a second plurality of diodes 10a, 10b, 10c, 10d. The diodes 10a, 10b, 10c, 10d allow for charging of the coupling capacitors whereas the diodes 4a, 4b, 4c, 4d charge the surge capacitors.

[0054] The secondary circuit 7 comprises an additional step-up level with a fifth capacitor 3e and a further diode 4e without coupling capacitor and without second diode. One terminal of the capacitor 3e is coupled directly to single secondary winding 11b, the other terminal of the capacitor 3e to the diode 4e which is configured to pass current from the single secondary winding 11b to the capacitor 3e. Due to the elimination of one coupling capacitor and one diode it becomes possible to reduce the number of components without observing a notable difference in the functionality of the device. The device can thus be realized with a smaller footprint which is an advantage when used in a medical device.

[0055] The second plurality of capacitors 3a, 3b, 3c, 3d and the fifth capacitor 3e are connected in series with each other and provide the high output voltage VO. The output voltage VO therefore depends on the number of step-up levels and the duty cycle of the charging process (see description below).

[0056] The individual connections of the various capacitors and diodes to each other are illustrated in more detail in the electrical circuit in FIG. 2a. By way of example, for the step-up level comprising elements 3a, 4a, 9a and 10a, the connections are as follows, including those with the neighboring step-up level. One terminal of the coupling capacitor 9a is connected to the cathode of the diode 10a and to the anode of the diode 4a. The cathode of the diode 4a is connected to the positive terminal of the capacitor 3a. The anode of the diode 10a and the cathode of the diode 4b of the adjacent step-up level are connected to the negative terminal of capacitor 3a. The other terminal of capacitor 9a is connected to the anode of the diode 4b, of one terminal of capacitor 9b, and the cathode of the diode 10b of the neighboring step-up level. The negative terminal of capacitor 3a is connected to the positive terminal of the neighboring capacitor 3b.

[0057] The diode 4a is thus configured to allow the current flow towards the surge capacitor 3a. The second diode 10a is configured to allow the current flow in the direction of the capacitor 9a.

[0058] An exemplary mode of operation of the step-up converter with a plurality of levels shown in FIG. 2a is as follows. During a first period of time, called primary phase, the switching device 2 is in the closed position. During the first period, the difference of the voltage VA supplied by the primary power source 1 and a voltage VD close to earth is applied to the first winding 11a of the transformer 11. The current rises to a maximum value Ipmax in the first circuit 6 and the first winding in the first period of time and, thus, the energy stored in the first winding reaches a value of approximately 0.5 Ipmax.sup.2 Lp, where Lp denotes the inductance of the first winding 11a. During the first period of time, as regards the secondary circuit 7, the coupling capacitors 9a through 9d are charged to the voltages of the output capacitors 3b through 3e by means of the diodes 10a through 10d. As soon as the coupling capacitors 9a through 9d are fully charged, the current flowing in the single secondary winding of the transformer 11 is nil due to the presence of the diodes 4a through 4e.

[0059] In a second period of time immediately following the first period of time, the switching device 2 is in an open state. By switching the switching device 2 into the open state, the current flow in the first circuit 6 of the step-up converter with a plurality of levels is interrupted. As a consequence, a current is induced in the second winding 11b of the transformer 11 and the secondary circuit 7. Energy is therefore transferred to the output capacitors 3a through 3e by means of the coupling capacitors 9a through 9d and the diodes 4a through 4e.

[0060] After the output capacitors 3a through 3e have stored the electrical energy supplied by the coupling capacitors 9a through 9d and the second winding 11b, the cycle is repeated until a desired predefined output voltage VO can be supplied by the output capacitors 3a through 3e.

[0061] The control of the switching device 2 can be effected by a control unit and the switching of the switching device can be based on signals provided, for example, by an oscillator circuit.

[0062] Another embodiment of a step-up converter with a plurality of levels similar to the one described hereinabove and similar in operation is shown in FIG. 2b. Similar elements are indicated by the same reference numbers.

[0063] When compared to the converter of FIG. 2a, the first circuit 6 additionally comprises an inductor 15 in series with the primary winding 11a and the switching device 2.

[0064] The presence of this inductance 15 allows for a reduction in the occurrence of a current surge when the switching device 2 is closed at the beginning of the first period described above. When the primary switch is closed in the first period, there is a voltage jump across the terminals of the single secondary winding 11b of the transformer 11, which causes a current surge in the recharge current Is of the coupling capacitors of the secondary circuit 7. This current surge is, moreover, multiplied by the turn ratio.

[0065] FIG. 2c and FIG. 2d illustrate two other methods for reducing the problem of the current surge in the primary period. Both methods may be realized by the converter according to FIG. 2a or according to FIG. 2b.

[0066] FIG. 2c shows the signal at the gate of the MOSFET as a function of the time at the beginning i and at the end f of a charging cycle of the surge capacitors 3a through 3e. FIG. 2c shows a charging principle with control of the duration of the first period Tp in relation to the duration of the second period Ts as a function of the time. The control of the duration of the primary period Tp during charging allows for the management of the current surge. We start with a first period Tpi that is low compared to the second period Tsi and we progressively increase its value over all or part of the charge. Towards the end of the charging of the surge capacitors, Tpf is greater than Tpi, while the second duration at the end Tsf is shorter than at the beginning Tsi. The duration of Ts can likewise evolve independently of Tp during the charging. As a consequence, T=Tp+Ts may likewise evolve during the charging of the capacitors, therefore Ti at the beginning of charging may be different from Tf at the end of charging.

[0067] FIG. 2d shows the current Ip in the first circuit 6 as a function of time. FIG. 2d therefore shows a charging principle with control of the primary current Ip. The control of the current Ip during charging likewise allows the management of the current surge. At the beginning of a charging cycle of the surge capacitors 3a through 3e, the maximum current Ipi in the primary circuit 6 is low and gradually increases its value over all or part of the charge until reaching a value 1pf>Ipi at the end of the cycle.

[0068] It is also conceivable to combine the approaches of FIG. 2c and FIG. 2d.

[0069] Another embodiment of a step-up converter with a plurality of levels that is similar to the one described hereinabove and similar in operation is illustrated in FIG. 3. Similar elements are indicated by the same reference numbers.

[0070] The step-up converter with a plurality of levels shown in FIG. 3 comprises a primary circuit 6 and a secondary circuit 7 which are galvanically isolated from each other. The primary circuit 6 comprises a primary power source 1, in particular a DC source, for example a battery or a series of batteries and a switching device 2, for example a MOSFET. The primary circuit moreover comprises a capacitor 12 connected in parallel to the primary power source 1. The capacitor 12 has a function of filtering the current of the primary power source 1.

[0071] Moreover, the primary circuit 6 comprises a first sensing means 13 for sensing the current flowing in the first winding and a second sensing means 14 for sensing of secondary oscillations at the end of the second period, which oscillations are sensed at the terminals of the switching device. The charge cycles can be controlled based on the signals respectively provided by the devices 13 and 14 for primary and secondary sensing. The end of the first period will intervene when the current through device 13 has reached a predefined value. The end of the second period will intervene when device 14 has sensed the oscillations that appear on the drain of the MOSFET at the moment in which the energy stored in the transformer 11 has been completely drained towards the surge capacitors.

[0072] The secondary circuit 7 comprises a first plurality of coupling capacitors 9a, 9b, 9c, 9d, 9e and a second plurality of (surge) capacitors 3a, 3b, 3c, 3d, 3e. In addition, the secondary circuit 7 comprises a first plurality of diodes 4a, 4b, 4c, 4d, 4e and a second plurality of diodes 10a, 10b, 10c, 10d, 10e. The individual connections of the various diodes and capacitors to each other can be seen in detail from the circuit of FIG. 3 and correspond to those of FIG. 2a.

[0073] In this embodiment, all the step-up levels therefore comprise a coupling capacitor, a surge capacitor and two diodes.

[0074] According to a variant, an inductance can be introduced in the primary circuit 6 as in the variant shown in FIG. 2b to reduce the current surge at the beginning of the primary period.

[0075] Another embodiment example of a step-up converter with a plurality of levels is shown in FIG. 4. This embodiment is similar to the other embodiments shown in FIG. 2b and in FIG. 3. The primary circuit 6 of the embodiment of FIG. 4 is the same as the one of the embodiment of FIG. 2a. The primary circuit 6 of the embodiment of FIG. 2b or 3 may also be used.

[0076] The secondary circuit 7 comprises six step-up levels, a first plurality of coupling capacitors 9a, 9b, 9c, 9d, 9e, 9f and a second plurality of (surge) capacitors 3a, 3b, 3c, 3d, 3e, 3f. Moreover, the secondary circuit 7 comprises a first plurality of diodes 4a, 4b, 4c, 4d, 4e, 4f and a second plurality of diodes 10a, 10b, 10c, 10d, 10e, 10f. However, unlike the embodiments of FIG. 2b and FIG. 3, the capacitors 9a, 9b, 9c, 9d, 9e, 9f are connected in parallel with each other instead of a series arrangement.

[0077] Thus, the voltages supplied by the capacitors can be better balanced compared to a series connection. The individual connections of the various semiconductor devices to each other can be seen in detail from the circuit diagram of FIG. 4.

[0078] It should be noted that in the configurations shown in FIG. 2a, FIG. 2b, FIG. 3 and FIG. 4, a single secondary winding is required. The turn ratio n, of turns of the single secondary winding ns to the turns of the single primary winding np, is given by n=ns/np. It is preferably equal to two or more. The higher the turn ratio n, the more the voltage withstand constraints of the primary circuit 6 are relaxed. The switching device 2 must, for example, withstand 40 V to 60 V, which translates into a relatively moderate maximum channel resistance and low gate charge for a predefined control voltage of the transistor device comprised in the switching device. Battery voltages VA of approximately 3 V, 6 V or 9 V can be raised to output voltages VO of approximately 750 V or even 1500 V. The output energy provided by the discharge of the surge capacitors 3a through 3f (which may have capacitances in the range of, for example, 100 ?F to 1 mF) may be in the range of, for example, 40 J to 100 J. The overall charging time can be less than 10 s. Electromagnetic interference due to current variations in the secondary circuit 7 can be kept to a level comparable to conventional flyback converters such as that described above with reference to FIG. 1a and FIG. 1b.

[0079] In the embodiments described hereinabove, a single secondary winding is comprised in the transformer of the step-up converter with a plurality of levels. However, the present invention is not limited to this. According to an alternative embodiment, more than one single secondary winding, for example, two secondary windings may be present. In this case, each winding of the secondary windings is associated with its plurality of step-up levels. FIG. 5 illustrates this configuration.

[0080] The step-up converter with a plurality of levels shown in FIG. 5 comprises a first circuit 6, at low voltage, and a second circuit 7, at high voltage, which are galvanically isolated from each other. The primary circuit 6 comprises a primary power source 1, in particular a DC source, for example, a battery or several batteries in series. The battery may be, for example, a lithium-manganese dioxide battery or a lithium-carbon monofluoride battery or a lithium-silver vanadium oxide battery and may provide a battery voltage VA in the range of 3 V, 6 V or 9 V. Moreover, the primary circuit 6 comprises a switching device 2, for example, comprising a transistor device, in particular, a MOSFET transistor. As shown in FIG. 2b, an additional inductance may be provided according to an alternative to reduce a current surge.

[0081] The step-up converter with a plurality of levels comprises a transformer 11. The transformer 11 comprises a primary winding 11a with np turns or coil forming part of the primary circuit 6 and two secondary windings 11b and 11c or coils forming part of the secondary circuit 7.

[0082] Three step-up levels are associated with each of the secondary windings of the transformer 11. The three step-up levels shown at the bottom are associated with the secondary winding 11b shown in FIG. 5 and comprise a first plurality of coupling capacitors 9a, 9b, 9c, a second plurality of surge capacitors 3a, 3b, 3c, a first plurality of diodes 4a, 4b, 4c, and a second plurality of diodes 10a, 10b, 10c. The other three step-up levels shown higher up are associated with the other of the secondary windings 11c shown in FIG. 5 and comprise a first plurality of coupling capacitors 9d, 9e, 9f, a second plurality of surge capacitors 3d, 3e, 3f, a first plurality of diodes 4d, 4e, 4f, and a second plurality of diodes 10d, 10e, 10f.

[0083] In a manner similar to the embodiment shown in FIG. 4, the capacitors 9a, 9b, 9c and the capacitors 9d, 9e, 9f are, respectively, connected in parallel to each other. It should be noted that the example shown in FIG. 5 is symmetrical with respect to the number of step-up levels (three here) of the two pluralities of step-up levels associated with the two secondary windings. It is, however, conceivable that more or less step-up levels are associated with one of the secondary windings of the transformer 11 than with the other secondary winding.

[0084] According to one alternative, the capacitors 9a and/or 9d and the diodes 10a and/or 10d may be eliminated as in the embodiment of FIG. 2a.

[0085] The configuration shown in FIG. 5 is more complex than those shown in FIG. 2a, FIG. 2b, FIG. 3, and FIG. 4. The device can, however, operate in a more efficient manner. In particular, the maximum voltage of the coupling capacitor that needs to be charged to the highest level, see capacitor 9f in FIG. 4, can be reduced by 50%, respectively for capacitors 9c and 9f in the configuration shown in FIG. 5.

[0086] Moreover, it should be noted that according to other embodiments, more than one transformer as shown in FIG. 2a, FIG. 2b, FIG. 3, FIG. 4 and FIG. 5 may be used in the step-up converter with a plurality of levels. In this case, the step-up converter with a plurality of levels may comprise a further transformer comprising another primary winding, in particular a further single primary winding, and another secondary winding, in particular a single secondary winding. FIG. 6 therefore depicts such a step-up converter with a plurality of levels of an implantable medical device comprising two transformers according to a fifth embodiment of the present invention.

[0087] In this fifth embodiment, the first circuit 6 comprises a primary power source 1 and a switching device 2 as in the first embodiments of the present invention. The converter likewise comprises two secondary circuits 7_1 and 7_2, each circuit having several step-up levels; here, by way of example, three step-up levels. In the embodiment of FIG. 6, the levels of the two secondary circuits are in parallel, as in the embodiment of FIG. 4 or FIG. 5. According to a variant, the levels of one of the two secondary circuits or of both secondary circuits may be in series as shown in FIG. 2a, FIG. 2b or FIG. 3.

[0088] The step-up converter with a plurality of levels comprises two transformers 11_1 and 11_2. Transformer 11_1 comprises a single primary winding 11_1a having np turns or coil being part of primary circuit 6 and a single secondary winding 11_1b with ns turns or coil forming part of the first secondary circuit 7_1. The transformer 11_2 comprises a single primary winding 11_2a with np turns or coil forming part of the primary circuit 6 and a single secondary winding 11_2b with ns turns or coil forming part of the second secondary circuit 7_2. In addition, the surge capacitors 3c and 3d are connected.

[0089] The embodiments of a step-up converter with a plurality of levels as described hereinabove can be used in an implantable defibrillator, in particular for a subcutaneous implantable cardioverter defibrillator, called S-ICD.

[0090] An example of a subcutaneous implantable cardioverter defibrillator (S-ICD) 21 is illustrated in FIG. 7. The subcutaneous implantable cardioverter defibrillator (S-ICD) 21 comprises a step-up converter with a plurality of levels as described hereinabove, not visible in FIG. 7, a subcutaneous lead 23, and a metal housing 33. As shown in FIG. 7, the housing 33 is implanted subcutaneously. The subcutaneous lead 23 is arranged in the parasternal region. The subcutaneous lead 23 comprises a plurality of electrodes 25a, 25b, 25c, 25d. It should, however, be noted that the number of electrodes is not limiting. In one variant, the subcutaneous lead 23 may comprise fewer than four electrodes. In another variant, the subcutaneous probe 23 may comprise more than four electrodes.

[0091] At least one of the electrodes 25a, 25b, 25c, 25d may be a sensing electrode configured to sense electrophysiological signals. At least one of the electrodes 25a, 25b, 25c, 25d may be a defibrillation electrode capable of delivering a defibrillation signal.

[0092] In one variant, an electrical dipole may be formed between an electrode of the subcutaneous probe 23 and the housing 33.

[0093] In another variant (not shown), cardiac hemodynamic sensors, such as an accelerometer, may be integrated with the subcutaneous probe 23, as well as with the housing 33 in order to sense hemodynamic signals.

[0094] In the case of sensing of a fibrillation event, particularly by means of one or a plurality of the sensing electrodes 25a, 25b, 25c, 25d, and a suitably configured sensing circuit, not shown in FIG. 7, the subcutaneous implantable cardioverter defibrillator (S-ICD) 21 is activated. Shocks may be delivered to the heart by means of a defibrillation electrode of the subcutaneous lead 23 by a shock circuit that is connected to the charged capacitors of one of the embodiments of the step-up converter with a plurality of levels described hereinabove. The shocks are delivered under the control of the control unit, not shown in FIG. 7, comprised in the subcutaneous implantable cardioverter defibrillator (S-ICD) 21. The control unit also controls the charging operation of the step-up converter with a plurality of levels of the subcutaneous implantable cardioverter defibrillator (S-ICD) 21.

[0095] All of the embodiments discussed hereinabove are not intended to be limitations but serve as illustrative examples of features and advantages of the invention. It should be understood that some or all of the features described hereinabove may also be combined in different ways.