FIELD OF THE INVENTION

The present invention relates to a system of a power device and a portable device for wireless charging of a battery of the portable device, which power device comprises an antenna to emit a magnetic field with a carrier frequency to power the portable device which comprises an antenna exposed to the magnetic field and connected via a matching stage to a rectifier stage, to rectify an antenna signal, and which portable device comprises a charge stage, to sense and limit the rectified antenna signal, to provide an input voltage at an input pin of a charger IC of the portable device that provides a first charge current at an output pin connected to the battery to charge the battery for a first period of time as power source with the constant first charge current, and wherein the portable device comprises a detuning stage to change the resonance frequency of the antenna of the portable device and that the charge stage is built to limit the input voltage for the charger IC by steering the detuning stage to detune the resonance frequency of the antenna of the portable device away from the carrier frequency of the magnetic field.

BACKGROUND OF THE INVENTION

Wireless charging is used for all kind of different portable devices like a mobile phone or earphones. The portable device just has to be dropped close-by a power device that generates and radiates a magnetic field via an antenna of the power device with the advantage that no wire is needed to charge the portable device. In some of these systems, the power device just radiates the magnetic field and some newer systems comprise a feedback loop from the portable device to the power device to regulate the power of the magnetic field.

Figure 1 shows such a system of a power device 1 and a portable device 2 with a battery 3, know to a person skilled in the art. Such a system is for instance described in the NFC Forum™ Technical Specification Version 1.0. The power device 1 called “poller” comprises an antenna 4 that radiates a magnetic field with the carrier frequency of 13,56MHz. The portable device 2 called “listener” comprises an antenna 5 exposed to the magnetic field emitted by the power device 1. A matching circuit 15 matches the impedance of the output pins of the antenna 5 to input pins of a rectifier 6 that uses a bridge rectifier to rectify the antenna signal and to provide a DC voltage. A charge stage 7 of the portable device 2 is used to charge the battery 3. As the charge stage 7 comprises a charger IC 8 that needs a power voltage of 5 V +/- 10% as input voltage Ui , a DC/DC converter and limiter 9 is used to sense the DC voltage provided by rectifier 6 to limit it to provide the appropriate input voltage Ui at an input pin 10 of charger IC 8.

Battery 3 is a Li-Ion battery that needs to be charged by charge stage 7 in different time periods with different charge currents Ic and charge voltages. Charge stage 7 furthermore comprises a digital control stage 13 that generates a power adjustment information 16 in case the input voltage Ui at input pin 10 and/or the charge current Ic to charge the battery 3 are too low or too high. Such power adjustment information 16 is provided by the digital control stage 13 to a Cless Communication stage 14, which complies to the NFC communication protocol to communicate the power adjustment information 16 to the power device 1. With this feedback loop from portable device 2 to power device 1, charge stage 7 can request more or less power in the magnetic field provided by the power device 1.

Figure 2 shows a time diagram of the charge current Ic in two different time periods T1 and T2 to load battery 3. Figure 2 furthermore shows the actual battery voltage UBAT and the input voltage Ui at input pin 10 of charge IC 8 during the time periods T1 and T2 to load battery 3 and during a ramp-up period TR to ramp-up from the constant first charge current Ic in the first time period T1 to the higher constant second charge current Ic in the second time period T2. Figure 2 furthermore shows power PL generated in the portable device 2 from the magnetic field to load battery 3, which power PL more or less can be calculated as PL = Ui * Ic and figure 2 shows power Pp generated by the power device 1 in the magnetic field. Lowest block of figure 2 shows power adjustment information 16 from the portable device 2 to the power device 1 to increase the power Pp generated by the power device 1 in the magnetic field at the end of time period T1.

As shown in figure 2, battery 3 is loaded by charger IC 8 with constant first charge current Ic during the first time period T1 until UBAT reaches a particular voltage. From this time on Li-Ion battery 3 may be loaded with the higher second charge current Ic in the second time period T2 until UBAT reaches a target voltage and loading switches in a third time period to constant voltage charging. At the end of the first time period T1 charge stage 7 ramps-up the charge current Ic what reduces the input voltage Ui as power PL generated in the portable device 2 is not enough to load battery 3 in the second time period T2 with the high second charge current Ic. Charge stage 7 therefore transmits a power adjustment information 16 to power device 1 to increase the power Pp generated by the power device 1 in the magnetic field. As this feedback loop takes some time to have effect for charge IC 8, input voltage Ui drops furthermore and reaches a V _reS et charger voltage level, what leads to a power-off reset of the charger IC 8 due to too low input voltage Ui. Charging of battery 3 therefore is interrupted for a short period of time, as can be seen in the drop of charge current Ic at the beginning of transition period TR, what is a disadvantage.

Due to the upfront communication of power adjustment information 16, the power device 1 increases its output power Pp at the beginning of transition period TR. Within portable device 2 this increased power PL leads to an increase of the junction temperature TL, because the high power has to be burnt internally until the charge state will leave the reset state and come to the point where it is switching again to the high second charge current Ic. After this transition time TR the junction temperature TL within the portable device 2 will decrease again, because most of the power is delivered to the battery 3. The high junction temperature TL while the transition period TR can cause problems, because it might exceed the maximum allowed junction temperature TL of the portable device 2, what is a disadvantage.

US 2017/0025897 Al discloses a system of a power device and a portable device and which power device is configured to wirelessly charge the battery of the portable device. The portable device comprises a charger stage to charge the battery with the energy from the rectified antenna signal of the antenna of the portable device. For maximal power transfer a matching stage tunes the antenna in resonance and the charge stage is configured to steer a detuning stage to detune the resonance of the antenna of the portable device away from the carrier frequency of the magnetic field to limit the rectified antenna signal as input voltage of the charger stage. This known system provides the disadvantage that the portable device may only detune the antenna to reduce the power transferred from the power device, but may not request more power if needed to charge the battery.

US 2019/334367 Al discloses a similar system as described above, but with more than one receiver. Several of these receivers receive power in a wireless manner and simultaneously to charge the battery of the portable device with more power.

US 2018/272130 Al discloses the transmission of a request by a receiver of such a system to interrupt power transmission at the power device simultaneously with detuning.

Furthermore WO 2015/080517 Al and US 2019/097448 Al disclose to charge a battery wireless. SUMMARY OF THE INVENTION

It is an object of the invention to provide a system of a power device and a portable device with a charger IC for wireless charging of the battery of the portable device to avoid an substantial increase of the junction temperature TL of the portable device during the transition period TR.

This object is achieved in a system according to claim 1.

This inventive concept enables that the portable device dynamically changes the resonance frequency of its antenna to take more or less power from the magnetic field generated by the power device during the process to load the battery of the portable device. As substantially only the amount of power needed to load the battery during the different charge phases of the battery is take from the magnetic field, there is less or no waste power in the portable device that needs to be transformed into heat. It is furthermore possible to reduce the PCB size, because there is no need to achieve such a low temperature coefficient to get rid of the heat compared to the state of the art solution.

The feedback loop enables to steer the power device to generate more or less power in the magnetic field. As this feedback loop takes some time to take effect with more or less power PL generated within the portable device, the inventive detuning provides a big advantage to dynamically reduce the power taken from the magnetic field during a change of the power in the magnetic field.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. The person skilled in the art will understand that various embodiments may be combined.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a system known to a person skilled in the art, which system comprises a power device and a portable device with charger IC to charge a battery wireless.

Figure 2 shows a time diagram of the charge current and other parameters to charge the battery of the portable device of the system according to figure 1.

Figure 3 shows a system according to the invention, which comprises a power device and a portable device with a detuning stage to charge a battery wireless. Figure 4 shows a time diagram of the charge current and other parameters to charge the battery of the portable device of the system according to figure 3.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 3 shows a first embodiment of a system 17 of a power device 1 and a portable device 18 with a battery 3 according to the invention. The same reference signs are used for stages that have the same technical function as already described in the system of figure 1 known to a person skilled in the art. Power device 1 called “poller” comprises an antenna 4 that radiates a magnetic field with the frequency of 13,56MHz. Power device 1 could be a charging device connected to the power grid or powered by a battery power pack. Portable device 18 called “listener” comprises an antenna 5 exposed to the magnetic field emitted by power device 1. Portable device 18 could be any device like e.g. earphones or a mobile phone with a wireless interface and a battery 3. A matching circuit 15 matches the impedance of the output pins of the antenna 5 to input pins of a rectifier 6 via a detuning stage 19. Rectifier 6 uses a bridge rectifier to rectify the antenna signal and to provide a DC voltage as input voltage at a charge stage 20. As charge stage 20 comprises a charger IC 8 that needs a power voltage of 5 V +/- 10% as input voltage Ui , a voltage limiter 21 is used to sense the DC voltage provided by rectifier 6 and to limit it to provide the appropriate input voltage Ui at an input pin 10 of charger IC 8.

Battery 3 is a Li-Ion battery that needs to be charged by charge stage 20 in different time periods with different charge currents Ic and charge voltages. Charge stage 20 furthermore comprises a digital control stage 24 that generates a power adjustment information 16 in case the input voltage Ui at input pin 10 and/or the charge current Ic to charge the battery 3 are too low or too high. Such power adjustment information 16 is provided by the digital control stage 24 to a Cless Communication stage 14, which complies to the NFC communication protocol to communicate the power adjustment information 16 to the power device 1. With this feedback loop from portable device 18 to power device 1, charge stage 20 can request more or less power in the magnetic field provided by the power device 1.

As shown in figure 4, battery 3 is loaded by charger IC 8 with constant first charge current Ic, which is about 10% of the maximal charge current Ic to be used for the particular battery 3, during the first time period T1 until UBAT reaches a particular voltage. From this time on Li-Ion battery 3 may be loaded with the higher second charge current Ic, which is close to 100% of the maximal charge current Ic to be used for the particular battery 3, in the second time period T2 until UBAT reaches a target voltage. From this time on loading switches in a third time period to constant voltage charging and charge current Ic is decreasing automatically according to the battery’s charging condition until the charger stops charging e.g. when the charging current has decreased to 10% of the maximum charging current. The principle to load a Li-Ion battery in these time periods is known to a person skilled in the art.

At the end of the first time period T1 charge stage 20 ramps-up the charge current Ic, what reduces the input voltage Ui as power PL generated in the portable device 2 is not enough to load battery 3 in the second time period T2 with the high second charge current Ic. Charge stage 20 therefore transmits a power adjustment information 16 to power device 1 to increase the power Pp generated by the power device 1 in the magnetic field. As this feedback loop takes some time input voltage Ui drops furthermore and reaches a Vreset charger voltage level what leads to a power-off reset of the charger IC due to too low input voltage Ui what would increase the junction temperature TL as no power is used to charge battery 3 and all power PL generated would have to be transformed into heat. To avoid that digital control stage 24 is built to steer detuning stage 19 with a detuning information Di shown in figure 4 to change the resonance frequency of the antenna of the portable device 18 and therefore is built to limit power PL and the input voltage Ui for the charger IC 8 by detuning the resonance frequency of the antenna 5. Detuning stage 19 may comprise one or more discrete capacities connected with switches parallel to the matching stage 15 and antenna 5, which capacities change the resonance frequency of the antenna 5. The detuning stage 19 therefore comprises at least two tuning configurations to tune the resonance frequency of the antenna 5 in a first tuning configuration closer to or exact to the carrier frequency of the magnetic field generated by power device 1 to provide a higher power PL and therefore a higher input voltage Ui at the input pin 10 of the charger IC 8 than in a second tuning configuration with the resonance frequency of the antenna 5 farer away from the carrier frequency of the magnetic field.

Due to the upfront communication of the power adjustment information 16 the power device 1 will increase its output power Pp. On portable device 2 side this high power PL would lead to an increase of the junction temperature TL. To overcome that problem the detuning stage 19 changes the resonance frequency of the portable device 2 away from the system resonance frequency and the incoming power PL will be reduced until the charge state 20 will leave the reset state and come to the point where it is switching again to the high second charge current IC. At this point in time digital control stage 24 is built to steer detuning stage 19 with a detuning information Dithat detuning stage 19 changes again the resonance frequency to the optimum for power transfer. By means of this de- and retuning during this transition time TR the system 17 can overcome the high junction temperature TL problem.

In the same or another embodiment of the invention charge stage 20 comprises a temperature sensor and wherein the charge stage 20 is built to steer the detuning stage 19 to detune the resonance frequency of the antenna 5 of the portable device 18 away from the carrier frequency of the magnetic field generated by the power device 1, if the sensed temperature TL reaches a maximum temperature limit. In this embodiment detuning stage 19 is used to ensure that overheat of the portable device 18 and/or charger IC 8 is prevented to avoid damages. As a possible next step charge stage 20 may generate the power adjustment information 16 for the power device 1 to decrease the power of the magnetic field, if the detuning stage 19 had to detune the resonance frequency of the antenna 5 of the portable device 18 to reduce the sensed temperature TL. In another embodiment of the invention the power adjustment information 16 for the power device 1 is generated to decrease the power of the magnetic field, if the detuning stage 19 had to detune the resonance frequency of the antenna 5 of the portable device 18 to reduce the input voltage Ui at the input pin 10 of the charger IC 8.

In another embodiment not covered by this invention two or more portable devices of the system are exposed to the magnetic field of the power device 1 to load the batteries of these portable devices. As all these portable devices may enter the magnetic field at different time instances and all of their batteries may be in different charge conditions, the feedback loop described above with a power adjustment information 16 from the portable device to increase or decrease the power Pp generated by power device 1 in the magnetic field is not possible. Therefore the portable devices have to deal with the power Pp generated by power device 1 as is. To achieve that a method may be used where the detuning stage detunes the resonance frequency of the antenna 5 of the portable device away from the carrier frequency of the magnetic field while the charger IC 8 charges the battery 3 with the first charge current Ic and where the resonance frequency of the antenna 5 of the portable device 18 is tuned to the carrier frequency of the magnetic field while the charger IC 8 charges the battery 3 with the second charge current Ic, which is higher than the first charge current Ic. Assuming that for a typical charging cycle of a battery 3 the battery 3 is never drained so much that the battery 3 has to be charged with the low first charge current Ic for a long time it is possible to start already with the high power Pp state on power device 1 side and detune the portable device 2 to the second tuning configuration from the beginning during the first time period Tl. When the digital control stage 24 at the end of the first time period T1 switches to high second charging current Ic, the digital control stage 24 only needs to switch detuning stage 19 to the tuned first tuning configuration state and by that the system 17 can overcome the reset of the charger IC 8 and can decrease the transition time TR without having any temperature issues.