METHOD FOR CHARGING A DEVICE, DEVICE AND CHARGER

Abstract

A method includes connecting a device to a charger and providing wireless charging in a state of charge by transferring energy wirelessly from a transmitter module of the charger to a reception module of the device. The device has a state of discharge in which energy is consumed. The device includes a charging connector, to which a charging input voltage adjustable by the charger is applied for charging. The device includes a switching connector for turning the device on and off. The device includes a switch connected to the switching connector and being switchable by the charging input voltage by setting the charging input voltage to an intermediate voltage. The charger sets the charging input voltage to the intermediate voltage for switching the switch and transitioning the device into an off state with the device turned off. A corresponding device and charger are also provided.

Claims

1. A method, comprising: connecting a device to a charger; wirelessly charging the device in a state of charge by wirelessly transferring energy from a transmitter module of the charger to a reception module of the device; consuming energy with the device in a state of discharge; providing the device with a charging connector receiving a charging input voltage being adjustable by the charger for charging; providing the device with a switching connector for turning the device on and off; providing the device with a switch connected to the switching connector and being switchable by the charging input voltage by setting the charging input voltage to an intermediate voltage; and using the charger to set the charging input voltage to the intermediate voltage for switching the switch and transitioning the device into an off state having the device turned off.

2. The method according to claim 1, which further comprises completing charging once the charging input voltage drops below a charging threshold voltage.

3. The method according to claim 2, which further comprises transitioning the device into the state of charge from the state of discharge or from the off state when the charging input voltage at least corresponds to the charging threshold voltage.

4. The method according to claim 3, which further comprises transitioning the device from the state of charge to an idle state when the charging input voltage is less than the charging threshold voltage and transitioning the device from the idle state into the state of discharge when the charging input voltage is less than a reset voltage.

5. The method according to claim 1, which further comprises: providing the switch as a transistor including a gate, a source, and a drain; connecting the gate to the charging connector and pulling the gate up to the charging input voltage by using a resistor; connecting the gate through the resistor to the source and to ground; and connecting the drain to the switching connector and connecting the source to ground.

6. The method according to claim 1, which further comprises transferring energy during charging by using a magnetic field, producing the magnetic field by using a transmitter coil of the transmitter module, receiving the magnetic field at a reception coil of the reception module, and driving the transmitter module to induce the intermediate voltage in the device for setting the charging input voltage to the intermediate voltage.

7. The method according to claim 6, which further comprises: providing the charger with a converter and an oscillator; using the oscillator to produce a current for producing the magnetic field by way of the transmitter module; using the converter to produce a converter voltage for operation of the oscillator; and setting the charging input voltage by using the converter voltage.

8. The method according to claim 7, which further comprises: controlling the converter voltage in dependence on a coupling factor between the transmitter module and the reception module; and producing the intermediate voltage by setting the converter voltage by initially determining the coupling factor and then using the coupling factor to determine the converter voltage required to produce the intermediate voltage.

9. The method according to claim 8, which further comprises: using the device to transmit a last charging input voltage applied to the charger during the charging, as a final charging input voltage; using the charger to store the current, used for operating the transmitter coil at a time of the final charging input voltage, as a final current; and receiving the final charging input voltage at the charger, whereupon the coupling factor then is determined in combination with the final current.

10. The method according to claim 1, which further comprises: providing each of the device and the charger with a respective communications unit, for an interchange of data; using the device to modulate the data for transfer; using the charger to receive and demodulate the data; and providing the charger with a demodulator circuit serving to demodulate and being used to additionally determine the current in the transmitter module.

11. The method according to claim 1, which further comprises providing the charger, in addition to the converter, with a voltage reference circuit for overall producing a converter voltage below a feedback reference voltage of the converter.

12. The method according to claim 1, which further comprises providing the charger with an emergency energy storage unit to set the intermediate voltage upon an interruption in an energy supply to the charger.

13. A device, comprising means for carrying out the method according to claim 1.

14. The device according to claim 13, wherein the device is a hearing aid.

15. A charger, comprising means for carrying out the method according to claim

Description

BRIEF DESCRIPTION OF THE FIGURES

[0066] FIG. 1 is a longitudinal-sectional view of a device and a charger;

[0067] FIG. 2 is an equivalent circuit diagram of the device and the charger of FIG. 1;

[0068] FIG. 3 is a block diagram of another representation of the device and the charger of FIG. 1;

[0069] FIG. 4 is a block diagram of another representation of the device of FIG. 1;

[0070] FIG. 5 is a diagram showing four operating states of the device of FIG. 1;

[0071] FIG. 6 is a block diagram of another representation of the charger of FIG. 1;

[0072] FIG. 7 is a diagram showing the charging input voltage as a function of the coupling factor;

[0073] FIG. 8 is a diagram showing the charging input voltage as a function of the converter voltage;

[0074] FIG. 9 is a flow chart showing four steps of a method;

[0075] FIG. 10 is a diagram showing the charging input voltage as a function of the converter voltage for two different transistors;

[0076] FIG. 11 is a diagram showing the charging input voltage and the voltage for consumers of the device as a function of time;

[0077] FIG. 12 is a diagram showing the voltages of FIG. 11 at a comparatively later time;

[0078] FIG. 13 is a demodulator circuit of the charger of FIG. 1;

[0079] FIG. 14 is a voltage reference circuit of the charger of FIG. 1; and

[0080] FIG. 15 is a flow chart showing eight steps of a method.

DETAILED DESCRIPTION OF THE INVENTION

[0081] Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a device 2 and a charger 4, which are suitable for carrying out the method described herein. The device 2 is connected to the charger 4 and there is wireless charging in a state of charge LZ by virtue of energy being transferred wirelessly from a transmitter module 6 of the charger 4 to a reception module 8 of the device 2. By way of example, the device 2 in FIG. 1 is a binaural hearing aid having two individual devices, and so accordingly two reception modules 8 are present, which are supplied by the transmitter module 6 of the charger. FIG. 2 shows an equivalent circuit diagram for the device 2 and the charger 4, and FIG. 3 then shows another representation of the device 2 and the charger 4. Only the device 2 is shown in FIG. 4. FIGS. 2, 3, and 4 are simplified in relation to FIG. 1 to the effect of only one reception module 8 and only one transmitter module 6, that is to say only one of the individual devices, being shown. However, the following explanations apply in general, independently of the number of transmitter modules 6 and reception modules 8, that is to say, depending on the configuration of the device 2 and charger 4, one or more reception modules 8 may be present and there may also be one or more transmitter modules 6 independently thereof.

[0082] The device 2 is switched off during charging and is in the state of charge LZ. The device 2 includes a charging connector 10, to which a charging input voltage V.sub.cc that is adjustable by the charger 4 is applied for charging purposes. The device 2 further includes a switching connector 12, for turning the device on and off. In this case, the charging connector 10 and the switching connector 12 are connectors of a power management module 14 (also referred to as PMIC), which accepts the charging input voltage V.sub.cc and uses the latter to charge an energy storage unit 16 of the device 2.

[0083] The device 2 also has a state of discharge EZ in which energy is consumed, specifically by one or more consumers 18. In the state of discharge EZ, the power management module 14 controls the provision of energy for the consumers 18 from the energy storage unit 16. Consequently, the device 2 receives energy from the charger 4 in the state of charge LZ and the device 2 consumes the energy in the state of discharge EZ.

[0084] In this case, “the device 2 is switched on” is understood to mean that the consumers 18 are supplied with energy by using the power management module 14, and “the device 2 is switched off” then is understood to mean that the consumers 18 are not supplied with energy but equally the power management module 14 may still consume energy. As a matter of principle, the device 2 is also switched on in the state of discharge EZ. Provided the description below refers to the device 2 being “switched off,” this is understood to mean that, firstly, the device 2 “is switched off” if it is switched on and, secondly, the device 2 “remains switched off” if it has already been switched off.

[0085] Moreover, the device 2 includes a switch 20 which is connected to the switching connector 12 and which is switchable by the charging input voltage V.sub.cc by virtue of the charging input voltage V.sub.cc being set to an intermediate voltage. The switch 20 is part of a switch-off circuit 22. The device 2 is now switched off by using the charger 4 by virtue of the latter setting the charging input voltage V.sub.cc to the intermediate voltage in such a way that the switch 20 is switched and the device 2 transitions into an off state AZ. Thus, the charger 4 sets the intermediate voltage, whereupon the device 2 transitions into the off state AZ. This is implemented, for example, when the charging is terminated or interrupted but in principle may also occur generally in the case of a fault, for example should the energy storage unit 16 overheat or have an overvoltage/overcurrent. Hence, an automatic switch off is realized by way of the charger 4 as soon as energy is no longer transferred to the device 2. Hence, the charger 4 initiates the transition of the device 2 into the off state AZ in which the device 2—unlike in the state of discharge EZ—no longer consumes any energy. In this case, the charger 4 uses the option of variably setting the charging input voltage V.sub.cc.

[0086] The device 2 shown herein only in exemplary fashion is a hearing aid which is used to provide for a user who has a hearing deficiency. To this end, the hearing aid includes a microphone 24 (in this case two microphones 24 for each individual device) which captures sound from the environment and generates an electrical input signal. For modification purposes, this is supplied to a signal processor not explicitly shown, which outputs as a result an electrical output signal, which is then converted back into sound and output to the user through a receiver 26 of the hearing aid. Instead of the microphone 24 and the receiver 26, other input and/or output transducers are also possible depending on the type of hearing aid. In this case, the hearing aid has a binaural form, but it could alternatively be monaural. The microphones 24, the receivers 26 and the signal processors are each consumers 18 of the device 2. Alternatively, the device 2 is a headphone, a headset, a wearable, a smartphone, or the like.

[0087] For charging, the device 2 is connected to the charger 4 and placed into the latter to this end, for example as shown in FIG. 1. To this end, the charger 4 shown herein is in the form of a charging tray with a depression 28 into which the device 2 is placeable. The charger 4 optionally has a lid 30. Expediently, the depression is shaped so that the device is held therein in an arrangement relative to the charging tray that is as defined as possible.

[0088] Depending on the charging level of the energy storage unit 16, the latter provides a voltage V.sub.bat for the consumers 18, that voltage optionally still being transformed by a transformation unit 32 in advance. The higher the charging level, the higher this voltage V.sub.bat typically is. The device 2 is charged by the charger 4 with a charging input voltage V.sub.cc, which is the voltage present in the device 2 for charging the energy storage unit 16. Then, the energy storage unit 15 is charged until the desired charging level or voltage Vbat has been reached. A charging threshold voltage V.sub.chg,thres is specified to this end, the latter being compared to the charging input voltage V.sub.cc in order to define when there is charging, and when not. In the present case, the charging is completed once the charging input voltage V.sub.cc drops below the charging threshold voltage V.sub.chg,thres. By way of example, the charging threshold voltage V.sub.chg,thres is a fixed voltage.

[0089] Although the automatic switch-off is carried out by the device 2 itself in the present case, it does not initiate this itself; instead, this is initiated by the charger 4 which determines when the device 2 should be switched off and which then transmits a switch-off signal to the device 2 in such a way that the latter is switched off. The switch-off signal leads to the intermediate voltage being present in the device 2.

[0090] It is desirable in general for the device 2 to be switched off after charging, for as long as the device still is connected to the charger 4. When the state of charge LZ is completed, the device 2 should not where possible transition into the state of discharge EZ and hence remain switched on; instead, the device 2 should be switched off.

[0091] In order to realize the automatic switch-off and thereby switch the device 2 off after charging, use is made of the charging connector 10 of the power management module 14. The charging input voltage V.sub.cc is applied to the charging connector 10. In an embodiment not explicitly shown, the switching connector 12 is pulled up using a pull-up resistor and a manually actuatable switch for manually switching the device 2 off is connected between the switching connector and ground 34. Independently thereof or suitably combined therewith, the device 2 includes the aforementioned switch-off circuit 22 with the switch 20 for the automatic switch-off by using the charger 4, the switch-off circuit using the charging connector 10 and the switching connector 12 in analogous fashion. In this case, the switch 20 is a transistor, specifically a MOSFET, having gate 36, source 38, and drain 40, that is to say with appropriate connectors. The gate 36 is connected to the charging connector 10 and pulled up to the charging input voltage V.sub.cc using a resistor 42. The resistor 42 connects the gate 36 to the source 38 and to ground 34. The drain 40 and the source 38 are connected to the switching connector 12 and to ground 24, respectively.

[0092] In the off state AZ now realized, the device 2 is connected to the charger 4 but switched off in the process and neither consumes energy itself nor receives energy from the charger 4. By contrast, the device 2 is switched off in the state of charge LZ, but still receives energy for operating the power management module 14, and is switched on and consumes energy in the state of discharge EZ. In order to switch between the state of charge LZ and the state of discharge EZ (in both directions), the device 2 still has an idle state WZ in the exemplary embodiment shown, and so a total of four operating states AZ, EZ, LZ, WZ are possible, which also preclude one another.

[0093] An exemplary dependence of the operating states AZ, EZ, LZ, WZ is shown in FIG. 5. The device 2 transitions into the state of charge LZ from the state of discharge EZ, from the off state AZ or from the idle state WZ if the charging input voltage V.sub.cc at least corresponds to the charging threshold voltage V.sub.chg,thres. The state of charge LZ remains active for as long as the charging input voltage V.sub.cc at least corresponds to the charging threshold voltage V.sub.chg,thres. The device 2 transitions from the state of charge LZ into the idle state WZ once the charging input voltage V.sub.cc is less than the charging threshold voltage V.sub.chg,thres. The device 2 transitions from the idle state WZ into the state of discharge EZ once the charging input voltage V.sub.cc is less than a reset voltage V.sub.rst and additionally in this case once a time that is longer than a discharge time t.sub.disc has also elapsed. In this case, the reset voltage V.sub.rst is fixed voltage and a parameter of the power management module 14, and serves to stop the operation of the latter and initialize the latter with a predefined standard state. In the present case, the reset voltage V.sub.rst is also used to define when the transition from the idle state WZ to the state of discharge EZ occurs. By way of example, the discharge time t.sub.disc is a fixed time of a few seconds. Conversely, the device 2 transitions from the state of discharge EZ into the idle state WZ if the charging input voltage V.sub.cc is less than the charging threshold voltage V.sub.chg,thres and greater than the reset voltage V.sub.rst, and transitions from the idle state WZ to the state of charge LZ if the charging input voltage V.sub.cc at least corresponds to the charging threshold voltage V.sub.chg,thres. The idle state WZ remains active for as long as the charging input voltage V.sub.cc is less than the charging threshold voltage V.sub.chg,thres.

[0094] The automatic switch off, that is to say a transition into the off state AZ, is realized by virtue of the charging input voltage V.sub.cc at the charging connector 10 being set to an intermediate voltage which is a gate-source threshold voltage V.sub.gs-thres of the transistor and lies between the reset voltage V.sub.rst and a minimum gate-source threshold voltage V.sub.gs-thres,min, that is to say a minimum value for the gate-source threshold voltage V.sub.gs-thres. The gate-source threshold voltage V.sub.gs-thres is the voltage required to switch the transistor and is in a range between the minimum gate-source threshold voltage V.sub.gs-thres,min and a maximum gate-source threshold voltage V.sub.gs-thres,max. The reset voltage V.sub.rst is greater than the actually used gate-source threshold voltage V.sub.gs-thres but the maximum gate-source threshold voltage V.sub.gs-thres,max may be greater than the reset voltage V.sub.rst.

[0095] Now, a voltage range used to transition into the off state AZ is spanned for the intermediate voltage between, firstly, the minimum gate-source threshold voltage V.sub.gs-thres,min and, secondly, the reset voltage V.sub.rst. If the charging input voltage V.sub.cc is less than the reset voltage V.sub.rst, the device 2 transitions into the state of discharge EZ. In principle, the state of discharge EZ initially is active for as long as the charging input voltage V.sub.cc is less than the minimum gate-source threshold voltage V.sub.gs-thres,min. The device 2 transitions into the off state AZ once the charging input voltage V.sub.cc is less than the reset voltage V.sub.rst and greater than the charging threshold voltage V.sub.chg,thres and additionally in this case once a time (during which the intermediate voltage is held) that is longer than a switching connector active time tsca has elapsed. Accordingly, as soon as the intermediate voltage has been reached at the gate 36, the transistor is switched and the switching connector 12 is pulled to ground 34. The device 2 transitions briefly into the state of discharge EZ and, from there, into the off state AZ after the switching connector active time tsca has elapsed. By way of example, the switching connector active time t.sub.sca is a fixed time of, e.g., a few seconds. In the present case, a transition into the off state AZ is only possible proceeding from the state of discharge EZ.

[0096] A switch-on of the device 2 and, specifically, a transition from the off state AZ into the state of discharge EZ is possible initially through the state of charge LZ. In the embodiment shown herein, the device 2 transitions from the off state AZ into the state of charge LZ if the charging input voltage V.sub.cc at least corresponds to the charging threshold voltage V.sub.chg,thres. Alternatively or in addition, a transition from the off state AZ is possible by way of a manual switch-on of the device 2 by the user. To this end, the device 2 includes a switch (e.g., as already described further above) that is not explicitly shown herein.

[0097] The described solution for the automatic switch-off of the device 2 is readily possible in the case of connected-by-contact charging since there is a conductive connection in this case, through the use of which the intermediate voltage can easily be set. However, in the case of a charger 4 for wireless charging as described herein this is not readily possible since the charging input voltage V.sub.cc is not provided directly by the charger 4, but merely induced in the device 2 thereby by using the transmitter module 6, and consequently is not necessarily present in the charger 4 itself.

[0098] As is evident in FIG. 2, there is an energy transfer during charging by using a magnetic field M which is produced using a transmitter coil 44 of the transmitter module 6 and which is received by a reception coil 46 of the reception module 8. In order to then set the charging input voltage V.sub.cc to the intermediate voltage in the case of a wireless charger 4, the transmitter module 6 is accordingly controlled in such a way that the intermediate voltage is induced in the device 2. The magnetic field M otherwise used for charging purposes consequently simultaneously represents the switch-off signal, which is transmitted from the charger 4 to the device 2, when actuated accordingly.

[0099] Together, the charger 4 and the device 2 for wireless charging form a wireless charging system. The reception module 8 provides the charging input voltage V.sub.cc and outputs the latter to the power management module 14. In general, the transmitter coil 44 in the transmitter module 6 is operated using a power source of the charger 4. Moreover, the reception module 8 includes wiring for the reception coil 46 in order to produce the charging input voltage V.sub.cc. In this case, the wiring includes a tuning capacitor 48, a smoothing capacitor 50 and a Schottky diode 52.

[0100] The charging input voltage V.sub.cc depends on a multiplicity of parameters, in particular on the current I.sub.tx to the transmitter coil 44, the respective inductance of the transmitter coil Ltx and of the reception coil L.sub.rx, a transfer frequency f, which is used for the transfer of energy by using the magnetic field M, and a coupling factor k. The coupling factor k in turn depends, in particular, on the distance A and on the angle of inclination between the transmitter coil 44 and the reception coil 46, that is to say in general on the spatial arrangement of the charger 4 and the device 2 during charging. The smaller the distance A and the smaller the angle of inclination, the greater the coupling factor k. In general, the following applies to the charging input voltage V.sub.cc: V.sub.cc∝2π.Math.f.Math.k.Math.√(L.sub.tx.Math.L.sub.rx).Math.I.sub.tx.

[0101] For the wireless energy transfer, the charger 4 still includes a converter 54 and an oscillator 56. This is shown in detail in FIG. 6. The oscillator 56 produces the current I.sub.tx for operating the transmitter coil 44 and accordingly is a power source. Then, the transmitter coil 44 and the oscillator 56 form the transmitter module 6. The converter 54 produces a converter voltage V.sub.dd for operating the oscillator 56. Consequently, the converter 54 influences the current I.sub.tx with which the transmitter coil 44 is operated. The charging input voltage V.sub.cc and hence also the intermediate voltage is thus set by using the converter voltage V.sub.dd.

[0102] For fixed values of the inductances L.sub.tx, L.sub.rx of transmitter coil 44 and reception coil 46 and of the transfer frequency f, the charging input voltage V.sub.cc increases with increasing coupling factor k and, at the same time, with increasing current I.sub.tx to the transmitter coil 44. These two relationships, specifically between charging input voltage V.sub.cc and coupling factor k on the one hand and between charging input voltage V.sub.cc and current I.sub.tx on the other hand, are used in the present case, given a known coupling factor k, to control the charging input voltage V.sub.cc by using the current I.sub.tx, and hence to activate the off state AZ in a targeted manner. The off state AZ of the device 2 is then activated externally by the charger 4 by way of a suitable control of the converter 54 and an adjustment of its converter voltage V.sub.dd. As described above, the relationship between converter voltage V.sub.dd and charging input voltage V.sub.cc is given by V.sub.cc∝2π.Math.f.Math.k.Math.√(L.sub.tx.Math.L.sub.rx).Math.I.sub.tx, with the current I.sub.tx, as described, being a function of the converter voltage V.sub.dd.

[0103] The converter voltage V.sub.dd which should be set to produce a certain charging input voltage V.sub.cc and the intermediate voltage depends on the coupling factor K and can therefore vary as a matter of principle. By contrast, the inductances L.sub.tx, L.sub.rx and the transfer frequency f are known for a given combination of device 2 and charger 4. Now, for the purposes of producing the intermediate voltage, the converter voltage V.sub.dd, and hence also the current I.sub.tx, is set in the present case by virtue of initially determining the coupling factor K and then using the latter to determine the converter voltage V.sub.dd that is required to produce the intermediate voltage. This is illustrated in FIGS. 7 and 8, and implemented on the basis of the relationship between charging input voltage V.sub.cc and converter voltage V.sub.dd, specifically V.sub.cc∝2π.Math.f.Math.k.Math.√(L.sub.tx.Math.L.sub.rx ).Math.I.sub.tx(V.sub.dd ).

[0104] As shown in FIG. 7, the coupling factor k is determined by way of the relationship between the charging input voltage V.sub.cc and the current I.sub.tx/converter voltage V.sub.dd, to be precise using a known pair of values for the charging input voltage V.sub.cc and the current I.sub.tx. Since the charging input voltage V.sub.cc is not known to the charger 4, there is communication between the charger 4 and the device 2 for determining the coupling factor k. At the end of the charging process, the device 2 transmits to the charger 4 the last charging input voltage V.sub.cc (more precisely: its value) applied during the charging. This last-applied charging input voltage V.sub.cc is also referred to as “final charging input voltage” V.sub.cc. Moreover, the charger 4 stores the current I.sub.tx (more precisely: its value) that is used to operate the transmitter coil 44 at the time of the final charging input voltage V.sub.cc, that is to say the last current I.sub.tx applied still during charging, which is analogously referred to as final current I.sub.tx. The final charging input voltage V.sub.cc is transmitted through a data connection between the device 2 and the charger 4. To this end, the device 2 and the charger 4 each have a communications unit 58, 60, for example an antenna and a suitable circuit for the antenna, for transmitting and/or receiving data, specifically the final charging input voltage V.sub.cc. The charger 4 receives the final charging input voltage V.sub.cc, whereupon the coupling factor k is determined in combination with the final current I.sub.tx, specifically by way of the specified relationship and, for example, as shown in FIG. 7.

[0105] Then, the converter voltage V.sub.dd of the converter 54 is determined using the intended intermediate voltage and the coupling factor k. Since the intermediate voltage is in a voltage range between the reset voltage V.sub.rst and the minimum gate-source threshold voltage V.sub.gs-thres,min, a suitable voltage range 62 then also arises accordingly, as shown in FIG. 8, for the converter voltage V.sub.dd, from which voltage range the latter then is chosen, for example simply as the mid-value of the voltage range 62.

[0106] In summary, setting of the converter voltage V.sub.dd described herein consequently includes the four steps S101-S104 shown in FIG. 9: A final current I.sub.tx and a final charging input voltage V.sub.cc are determined in a first step S101. Subsequently, the coupling factor k is determined on the basis of the final current I.sub.st and the final charging input voltage V.sub.cc in a second step S102. The converter voltage V.sub.dd required to this end is subsequently determined in a third step S103 using the coupling factor k and the intended intermediate voltage, and the required converter voltage is finally set in a fourth step S104.

[0107] The relationship used in each case for determining the coupling factor k and the converter voltage V.sub.dd is for example stored in each case as a parameterized functional bundle, as shown in FIGS. 7 and 8. In order to determine the coupling factor k, the charging input voltage V.sub.cc is for example stored as a function of the coupling factor k and parameterized by the current I.sub.tx, as shown in FIG. 7, in such a way that a corresponding functional bundle arises. In order to determine the converter voltage V.sub.dd, the charging input voltage V.sub.cc is for example stored as a function of the converter voltage V.sub.dd and parameterized by the coupling factor k, as shown in FIG. 8, in such a way that a corresponding functional bundle arises.

[0108] In the example of FIG. 7, the final charging input voltage V.sub.cc is 7.6 V and the associated final current I.sub.tx is 0.5 A. The coupling factor k is determined to be k=0.07 on the basis of these values and in conjunction with the inductances L.sub.tx, L.sub.rx and the transfer frequency f. The reset voltage V.sub.rst is 2 V and the minimum gate-source threshold voltage V.sub.gs-thres,min is 1 V; then a voltage range of 1 V to 2 V arises for the intended intermediate voltage. According to the example in FIG. 8, a converter voltage V.sub.dd in the range of 0.125 V to 0.275 V is then determined for this intermediate voltage using the coupling factor of k=0.07. Then, the converter voltage V.sub.dd is set to 0.2 V, for example, in such a way that the corresponding intermediate voltage arises in the device 2 and the device 2 transitions into the off state AZ.

[0109] The gate-source threshold voltage Vgs-thres must, at least in certain regions, be smaller than the reset voltage V.sub.rst. For the aforementioned reset voltage V.sub.rst of 2 V, a suitable transistor therefore has a minimum gate-source threshold voltage V less than 2 V, for example 1.4 V or 0.7 V. gs-thres,min of

[0110] For all distances A, the reset voltage V.sub.rst defines an upper limit for the converter voltage V.sub.dd (reference is made in this case to distance A for simplicity; however, the explanations apply in general to the coupling constant k). In the case of the aforementioned reset voltage V.sub.rst of 2 V, the upper limit for the converter voltage V.sub.dd is 0.69 V, for example. Should it not be possible to maintain the latter, an automatic switch-off may not be possible for some distances A under certain circumstances. This is illustrated in FIG. 10. By way of example, the distance A for charging purposes is between 1 mm and 10 mm (FIG. 10 plots the charging input voltage V.sub.cc as a function of the converter voltage V.sub.dd for different distances A from 1 mm to 7 mm in 1 mm steps). In order to facilitate an automatic switch-off for all distances A, the charging input voltage V.sub.cc must be above the gate-source threshold voltage V.sub.gs-thres for each distance A. Automatic switch-off is not possible for those distances A that do not satisfy this condition. From this, it is evident that a transistor with a minimum gate-source threshold voltage V.sub.gs-thres,min that is as low as possible facilitates an automatic switch-off for a significantly larger range of distances A. In the aforementioned example with a transistor which has a minimum gate-source threshold voltage V.sub.gs-thres,min of 0.685 V, the voltage range 64 available to the converter voltage V.sub.dd for producing a suitable intermediate voltage for automatic switch-off at all distances A is only 0.005 V. Then, a lower converter voltage V.sub.dd possibly no longer suffices for an automatic switch-off at a distance A of 5 mm or more. Using another transistor which has a minimum gate-source threshold voltage V.sub.gs-thres,min of 0.5 V, the voltage range 66 available to the converter voltage V.sub.dd for producing a suitable intermediate voltage for the automatic switch-off at all distances A is approximately 0.2 V. Hence, an automatic switch-off is possible without problems over the entire range from 1 mm to 10 mm.

[0111] FIGS. 11 and 12 each show an oscilloscope measurement in an exemplary application. In this case, the charging input voltage V.sub.cc and the voltage Vout output by the power management module 14 to the consumers 18 are each plotted as a function of time t. The distance A between transmitter coil 44 and reception coil 46 is 4 mm in this case. The device 2 initially transitions into the state of charge LZ and is charged. Then, as shown in FIG. 11, the converter voltage V.sub.dd of the converter 54 is set to 0.6 V for the automatic switch-off. Hence, the charging input voltage V.sub.cc in the device 2 is set to an intermediate voltage of 1.5 V. The device 2 initially transitions into the state of discharge EZ and starts to consume energy a few seconds later, for the purposes of which the power management module 14 provides a voltage Vout of, e.g., 1.3 V for the consumers 18. Then, the device 2 transitions into the off state AZ, which then is active in FIG. 12. After a few seconds (e.g. s), the converter voltage V.sub.dd is set to 0 V in order to deactivate the converter 54 so that the charging input voltage V.sub.cc then is 0 V, as shown in FIG. 12. Now, the charger 4 can be switched off overall and separated from the device 2, with the device 2 then remaining in the off state AZ without returning to the state of discharge EZ even though the charging input voltage V.sub.cc is 0 V in that case.

[0112] As already described, the device 2 and the charger 4 each have a respective communications unit 58, 60, for the interchange of data. With the communications unit 58 of the device 2, the communications unit 60 of the charger 4 forms a communications system for data interchange. In the present case, the communications system serves to transmit data in relation to the charging input voltage V.sub.cc from the device 2 to the charger 4. Accordingly, the communications system can have a bidirectional configuration or only be monodirectional from the device 2 to the charger 4. In this case, the communications system is wireless and uses an appropriate communications protocol, for example magnetic induction. In the present case, the data are modulated by the device 2 for transfer purposes. The transferred data are, for example, the state of charge (SOC), current voltage, current charging current, temperature, the above-described charging input voltage V.sub.cc of the energy storage unit 16 or a combination thereof. The charger 4 receives and demodulates the data. To this end, the charger 4 includes a demodulator circuit 68, for example as shown in FIG. 13. The demodulator circuit 68 shown there is also used to determine the current I.sub.tx in the transmitter module 6, more precisely the current I.sub.tx through the transmitter coil 44, which is integrated in the demodulator circuit 68 to this end. To this end, the demodulator circuit 68 includes a capacitor 70, at which the current I.sub.tx emerges as a ratio of a maximum object detection voltage VOD of the demodulator circuit 68 and its impedance at the transfer frequency f of the transmitter coil 44.

[0113] In the case of a connected-by-contact automatic switch-off, the converter 54 outputs a voltage between the reset voltage V.sub.rst and the minimum gate-source threshold voltage Vgs-thres,min as converter voltage V.sub.dd in order to switch the device 2 off. However, this voltage range for the converter voltage V.sub.dd is not necessarily applicable to the wireless automatic switch-off since a lower converter voltage V.sub.dd is required for the switch-off in this case. In the case of the wireless automatic switch-off, the converter voltage V.sub.dd of the converter 54 is an input voltage for the oscillator 56 which amplifies the converter voltage V.sub.dd in such a way that, ultimately, an appropriate greater charging input voltage V.sub.cc arises in the device 2, especially if the reception coil 46 has more turns than the transmitter coil 44. Therefore, the converter voltage V.sub.dd is substantially lower in the case of the wireless automatic switch-off than in the case of the connected-by-contact automatic switch-off, and is of the order of millivolts, for example. Typically, the converter 54 is unable to produce a converter voltage V.sub.dd below an internal feedback reference voltage V.sub.fb related to the converter 54, which is typically at least 0.6 V. Therefore, in addition to the converter 54, the charger 4 shown herein includes a voltage reference circuit 72 in order overall to produce a converter voltage V.sub.dd below the feedback reference voltage V.sub.fb of the converter 54. One exemplary embodiment of such a voltage reference circuit 72 is shown in FIG. 14 and has an external reference voltage Vref related to the converter 54, which is connected to a feedback connector 74 of the converter 54. The external reference voltage Vref is greater than the internal feedback reference voltage V.sub.fb. Then, the voltage reference circuit 72 is configured and connected to the converter 54 so that the converter voltage V.sub.dd arises as a difference between, firstly, the internal feedback reference voltage V.sub.fb and, secondly, the difference between external reference voltage Vref and internal feedback reference voltage V.sub.fb, weighted by a suitable resistance ratio R1/R2 of two resistors 76, 78, i.e., V.sub.dd=V.sub.fb−R1.Math.(V.sub.ref—V.sub.fb)/R2. The two resistors 76, 78 form a voltage divider with two endpoints 80, to which, firstly, an output 82 of the converter 54 and, secondly, the external reference voltage Vref are connected, and with a midpoint 86 between the two resistors 76, 78, to which the feedback connector 74 is connected.

[0114] Further, the charger 4 includes a control unit 86, to which the communications unit 58 and the converter 54 are connected. The converter 54 is set by using the control unit 86, specifically on the basis of the data received by using the communications unit 58. The charger 4 still optionally includes an emergency energy storage unit 88 in order to nevertheless set the intermediate voltage and produce the switch-off signal to this end when the energy supply to the charger 4 is interrupted.

[0115] In an embodiment, the control unit 86 is configured to carry out one or more of the steps of the method described herein. The device 2 also includes a control unit 90 which is configured in an embodiment to carry out one or more of the steps of the method described herein.

[0116] Overall, a method is realized by the switch-off circuit 22 in combination with the communications system, within the scope of which there is a wireless automatic switch-off of the device 2 initiated by the charger 4, specifically at the end of a charging process of the energy storage unit 16 of the device 2 and in general when an energy transfer from the charger 4 to the device 2 is interrupted. To this end, the method for example includes one or more of the steps shown in FIG. 15, preferably in the specified sequence. In a first step S201, the device 2 sends data to the charger 4, for example recurrently. The data are analyzed in a second step S202, for example by the control unit 86. To the extent the data are modulated, these are initially demodulated in the second step S202, for example by using the above-described demodulator circuit 68. The converter 54 is set on the basis of the data, for example by the control unit 86, in a third step S203. By way of example, the control unit 86 sets the converter 54 using a DAC signal or a PWM signal. In a fourth step S204, the converter 54 subsequently outputs a converter voltage V.sub.dd to the oscillator 56 and controls the latter as a result. Likewise in the fourth step S204, the oscillator 56 outputs a current I.sub.tx used then to operate the transmitter coil 44. Consequently, the current 6 is set indirectly by the converter 54 in the fourth step S204. The transmitter coil 44 produces a magnetic field M on the basis of the current I.sub.tx in a fifth step S205. The magnetic field M is received in a sixth step S206 by the reception coil 46, the latter producing a charging input voltage V.sub.cc in the device 2 on the basis thereof in such a way that, overall, the charger 4 induces a charging input voltage V.sub.cc in the device 2. Then, the device 2 is switched off in a seventh step S207 should the charging input voltage V.sub.cc be in the voltage range between the reset voltage V.sub.rst and the minimum gate-source threshold voltage V.sub.gs-thres,min, that is to say if the charging input voltage V.sub.cc is an intermediate voltage as described above. Accordingly, the device 2 transitions into the off state AZ in the seventh step S207 if an intermediate voltage is present, and is then switched off. In the seventh step S207, the device 2 optionally only transitions into the off state AZ after a time t that is longer than a switching connector active time tsca has additionally elapsed, as described above. Ultimately, the automatic switch-off is implemented on the basis of data transmitted to the charger 4 by the device 2. In an optional eighth step S208, the converter 54 is finally also deactivated, preferably after a certain period of time t, for example 10 s, following the transition of the device 2 into the off state AZ.

[0117] The description until now has considered the device 2 being switched off once the charging has been completed. Then, the data contain at least the final charging input voltage V.sub.cc, which is determined in conjunction with the final current I.sub.tx and which is also used in combination therewith by the control unit 88, in particular, in order to determine a converter voltage V.sub.dd and then set the converter. However, other events than the completion of the charging process are likewise suitable, in principle, for initiating the automatic switch-off, for example if a temperature of the energy storage unit 16 exceeds a limit temperature (overheating), if voltage or current at the energy storage unit 16 exceed a corresponding limit (overvoltage/overcurrent), and generally in the case of a flaw of the energy storage unit 16 (fault), or similar events. Then, the control unit 86 infers one or more of these events when the control unit 86 analyzes the data, and then controls the converter 54 accordingly in order to initiate the automatic switch-off.

[0118] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention.

LIST OF REFERENCE SIGNS:

[0119] 2 Device [0120] 4 Charger [0121] 6 Transmitter module [0122] 8 Reception module [0123] 10 Charging connector [0124] 12 Switching connector [0125] 14 Power management module [0126] 16 Energy storage unit [0127] 18 Consumer [0128] 20 Switch [0129] 22 Switch-off circuit [0130] 24 Microphone [0131] 26 Receiver [0132] 28 Depression [0133] 30 Lid [0134] 32 Transformation unit [0135] 34 Ground [0136] 36 Gate [0137] 38 Source [0138] 40 Drain [0139] 42 Resistor [0140] 44 Transmitter coil [0141] 46 Reception coil [0142] 48 Tuning capacitor [0143] 50 Smoothing capacitor [0144] 52 Schottky diode [0145] 54 Converter [0146] 56 Oscillator [0147] 58 Communications unit (of the device) [0148] 60 Communications unit (of the charger) [0149] 62 Voltage range (for the converter voltage) [0150] 64 Voltage range [0151] 66 Voltage range [0152] 68 Demodulator circuit [0153] 70 Capacitor [0154] 72 Voltage reference circuit [0155] 74 Feedback connector [0156] 76 Resistor [0157] 78 Resistor [0158] 80 Endpoint [0159] 82 Output [0160] 84 Midpoint [0161] 86 Control unit (of the charger) [0162] 88 Emergency energy storage unit [0163] 90 Control unit (of the device) [0164] A Distance [0165] AZ Off state [0166] EZ State of discharge [0167] I.sub.tx Current [0168] k Coupling factor [0169] L.sub.rx Inductance of the reception coil [0170] L.sub.tx Inductance of the transmitter coil [0171] LZ State of charge [0172] M Magnetic field [0173] S101-S104 Step [0174] S201-S208 Step [0175] t.sub.disc Discharge time [0176] t.sub.sca Switching connector active time [0177] V.sub.bat Voltage [0178] V.sub.cc Charging input voltage [0179] V.sub.chg,thres Charging threshold voltage [0180] V.sub.dd Converter voltage [0181] V.sub.fb Feedback reference voltage [0182] V.sub.gs-thres Gate-source threshold voltage [0183] V.sub.gs-thres,max Maximum gate-source threshold voltage [0184] V.sub.gs-thres,min Minimum gate-source threshold voltage [0185] V.sub.OD Object detection voltage [0186] V.sub.out Voltage (from the power management module to consumers) [0187] V.sub.ref Reference voltage [0188] V.sub.rst Reset voltage [0189] WZ Idle state [0190] t Time