Battery charging system

One example includes a battery charging system configured to charge a battery associated with a mobile device. The battery charging system includes a transformer configured to receive an AC charging current via a charging cable at a primary inductor and to generate an AC secondary current at a secondary inductor. The battery charging system also includes a rectifier system configured to rectify and filter the AC secondary current to generate a DC charging current that is provided to charge the battery.

TECHNICAL FIELD

This disclosure relates generally to electronic systems, and more specifically to a battery charging system.

BACKGROUND

Wireless electronic devices, such as wireless communications devices (e.g., smart-phones), laptop computers, and tablet computers, are becoming more prevalent in modern consumer culture. Such devices are battery-powered, and thus require periodic charging to maintain sufficient battery voltage to operate the respective device. Charging a wireless device typically involves providing a DC voltage via a charging cable (e.g., a universal serial bus (USB) cable), which can take a considerable amount of time to charge fully (e.g., more than an hour from approximately zero volts). Charging a device in significantly less time can be accomplished by delivering a very high current, which is impractical or prohibitive with connector and cable dimensions of typical mobile devices. Alternatively, a very high voltage can be implemented, but such a charging system would require a highly inefficient step-down DC-DC converter, as well as significantly large circuit components in the mobile device.

SUMMARY

One example includes a battery charging system configured to charge a battery associated with a mobile device. The battery charging system includes a transformer configured to receive an AC charging current via a charging cable at a primary inductor and to generate an AC secondary current at a secondary inductor. The battery charging system also includes a rectifier system configured to rectify and filter the AC secondary current to generate a DC charging current that is provided to charge the battery.

Another example includes a method for charging a battery associated with a mobile device. The method includes receiving a power voltage at an AC adapter and generating an AC charging current based on the power voltage via a programmable AC current source associated with the AC adapter. The AC charging current can be provided on a first conductor of a charging cable that interconnects the AC adapter and the mobile device. The method also includes receiving a control voltage on a second conductor of the charging cable. The control voltage can include a voltage associated with the AC charging current and a DC feedback control voltage. The method further includes adjusting an amplitude of the AC charging current based on an amplitude of the DC feedback control voltage.

Another example includes a battery charging system. The system includes an AC adapter comprising a programmable AC current source configured to generate an AC charging current having an amplitude that is based on an amplitude of a DC feedback control voltage. The system also includes a device power system associated with a mobile device. The device power system includes a transformer configured to receive the AC charging current via a first conductor of a charging cable at a primary inductor and to generate an AC secondary current at a secondary inductor. The device power system also includes a rectifier system configured to rectify the AC secondary current to generate a DC charging current that is provided to charge a battery associated with the mobile device. The device power system further includes a charge controller configured to monitor an amplitude of a battery voltage and an amplitude of the AC charging current and to generate the DC feedback control voltage that is provided to the AC adapter via a second conductor of the charging cable.

DETAILED DESCRIPTION

This disclosure relates generally to electronic systems, and more specifically to a battery charging system. The battery charging system includes an AC adapter that can receive a power voltage (e.g., an AC line voltage) and is configured to generate a high-frequency (e.g., greater than approximately 500 kHz) AC charging current. The AC adapter can include a programmable AC current source to generate the AC charging current, such that the programmable AC current source can generate the AC charging current at an amplitude that is based on a DC feedback control voltage. The AC charging current is provided to the mobile device via a first conductor of a charging cable (e.g., a universal serial bus (USB) cable, such as a USB Type-C cable).

The mobile device includes a device power system that receives the AC charging current via the charging cable. The AC charging current is provided through a primary inductor of a transformer to generate an AC secondary current via a secondary inductor of the transformer. The AC secondary current is rectified and filtered to generate a DC charging current that is provided to charge the battery of the mobile device. In addition, the device power system includes a charge controller that monitors an amplitude of the AC charging current and an amplitude of the battery voltage, and generates the DC feedback control voltage at an amplitude that is based on the amplitudes of the AC charging current and the battery voltage. The DC feedback control voltage is added to the AC charging current on a second conductor of the charging cable, between isolation capacitors associated with the AC adapter and the device power system, respectively, such that the DC feedback control voltage can be provided to the programmable AC current source to set the amplitude of the AC charging current in a feedback manner.

FIG. 1illustrates an example of a battery charging system10. The battery charging system10can be implemented for charging a battery associated with a variety of different types of mobile devices, such as smart phones, laptop computers, tablet computers, or a variety of other wireless devices. As described herein, the battery charging system10can implement very fast charging of the battery (e.g., 1500 mA/h), such as to charge a battery to approximately 50% of battery capacity within approximately five minutes.

The battery charging system10includes an AC adapter12that is configured to generate an AC charging current ICHGin response to a power voltage VLINE. As an example, the power voltage VLINEcan be an AC line voltage that is provided, for example, from a public utility power grid. In the example ofFIG. 1, the AC adapter12includes a programmable AC current source14that is configured to generate the AC charging current ICHGin response to a control voltage VCTRL. As an example, the AC charging current ICHGcan have a high frequency (e.g., greater than approximately 500 kHz). As described in greater detail herein, the control voltage VCTRLcan correspond to a voltage associated with the AC charging current ICHGand a DC feedback control voltage. Thus, the programmable AC current source14can generate the AC charging current ICHGto have an amplitude that is based on an amplitude of the DC feedback control voltage component.

The AC charging current ICHGis provided on a first conductor of a charging cable16that interconnects the AC adapter12and a device power system18. As an example, the charging cable16can be configured as a universal serial bus (USB) cable (e.g., a USB Type-C cable). For example, the device power system18can be provided in the respective mobile device, such that the charging cable16can plug into the mobile device to interact with the device power system18to charge a battery20associated with the device power system18. The device power system18includes a transformer22that is configured to isolate the AC charging current ICHGfrom the battery20by generating an AC secondary current. The AC secondary current is rectified and filtered by a rectifier stage24to generate a DC charging current that charges the battery20. Based on the high frequency and high amplitude of the AC charging current ICHG, the DC charging current can provide very rapid charging of the battery20.

The device power system18also includes a charge controller26that is configured to provide feedback control of the AC charging current ICHG. As an example, the charge controller26can be configured to monitor an amplitude of both the AC charging current ICHGand the battery voltage, and can generate a DC feedback control voltage. The DC feedback control voltage can be added to the voltage associated with the AC charging current ICHGto provide the control voltage VCTRLthat is provided to the AC adapter12via a second conductor of the charging cable16. The programmable AC current source14can thus adjust an amplitude of the AC charging current ICHGbased on an amplitude of the DC feedback control voltage in the control voltage VCTRL. Accordingly, the programmable AC current source14can be configured to generate the AC charging current ICHGin a feedback manner to provide rapid charging of the battery20.

FIG. 2illustrates another example of a battery charging system50. The battery charging system50can correspond to a more detailed example of the battery charging system10in the example ofFIG. 1. Thus, the battery charging system50can be implemented for charging a battery associated with a variety of different types of mobile devices, such as smart phones, laptop computers, tablet computers, or a variety of other wireless devices in a very rapid manner.

The battery charging system50includes an AC adapter52that is configured to generate an AC charging current ICHGin response to a power voltage VLINE. As an example, the power voltage VLINEcan be an AC line voltage that is provided, for example, from a public utility power grid. In the example ofFIG. 2, the AC adapter52includes a programmable AC current source54that is configured to generate the AC charging current ICHG. For example, the programmable AC current source54can have a compliance range that can span from zero volts to approximately 40 volts RMS open-circuit, and can be deactivated by the AC adapter52in response to an open-circuit condition. As an example, the AC charging current ICHGcan have a high frequency (e.g., greater than approximately 500 kHz), and can have a sinusoidal or other waveform shape. The AC charging current ICHGis provided on a first conductor of a charging cable56that can correspond to any of a variety of typical charging cables, such as a USB cable (e.g., a USB Type-C cable).

In the example ofFIG. 2, the programmable AC current source54is configured to generate the AC charging current based on a control voltage VCTRL. As described in greater detail herein, the control voltage VCTRLcan correspond to a voltage associated with the AC charging current and with a DC feedback control voltage VFB. In the example ofFIG. 2, the AC adapter52includes an isolation capacitor C1that interconnects a second conductor of the charging cable56and a low-voltage power rail, demonstrated in the example ofFIG. 2as ground. Therefore, the programmable AC current source54can generate the AC charging current ICHGto have an amplitude that is based on an amplitude of the DC feedback control voltage VFB, which can correspond to an average voltage across the isolation capacitor C1.

The charging cable56interconnects the AC adapter52and a device power system58that can be located in the respective mobile device. Therefore, the charging cable56can be plugged into the mobile device to charge a battery B1associated with the device power system58. In the example ofFIG. 2, the device power system58includes a transformer T1that includes a primary inductor L1and a secondary inductor L2that are magnetically coupled. The AC charging current ICHGis provided from the first conductor of the charging cable56to the primary inductor L1, which thus induces an AC secondary current ISECin the secondary inductor L2. Thus, the transformer T1provides isolation of the AC charging current ICHGand the battery B1, such that the battery B1and/or other components of the device power system58are protected from short circuits associated with the AC charging current ICHG. Accordingly, the transformer T1of the device power system58obviates the need for disconnect/isolation switches at the connection pins associated with the charging cable56.

The AC secondary current ISECis provided through a rectifier. In the example ofFIG. 2, the rectifier is formed by a set of transistors N1, N2, N3, and N4that can operate as a synchronous bridge, such that the transistors N1, N2, N3, and N4can be switched in response to zero current across the respective transistors N1, N2, N3, and N4. The rectified AC secondary current ISECis filtered via an LC filter formed by an inductor LFand a capacitor CFto generate a DC charging current IDC. The DC charging current IDCcan thus be provided to charge the battery B1. While the rectifier stage in the example ofFIG. 2is demonstrated as a combination of the synchronous bridge formed by the transistors N1, N2, N3, and N4and the LC filter formed by the inductor LFand the capacitor CF(e.g., collectively corresponding to the rectifier stage24in the example ofFIG. 1), it is to be understood that other rectifiers and/or filters can be implemented to generate the DC charging current IDCbased on the AC secondary current ISEC.

The device power system58also includes a charge controller60that is configured to provide feedback control of the AC charging current ICHG. In the example ofFIG. 2, the charge controller60is configured to monitor an amplitude of a battery voltage VBATand an amplitude of the AC charging current ICHGbased on a charging voltage VCHG. The device power system58includes a sense resistor RSthat is coupled to the primary inductor L1and ground, such that the charge controller60monitors the charge voltage VCHGat a monitoring node62that is coupled to the other end of the sense resistor RS. Thus, the charging voltage VCHGhas an amplitude that is proportional to the amplitude of the charging current ICHGthrough the primary inductor L1. In response to the battery voltage VBATand the charging voltage VCHG, the charge controller generates the DC feedback control voltage VFBthat has an amplitude based on a desired amplitude of the charging current ICHGbased on a continuous amplitude of the battery voltage VBAT.

The device power system58also includes an isolation capacitor C2that interconnects the monitoring node62and the second conductor of the charging cable56. In the example ofFIG. 2, the charge controller60provides the DC feedback control voltage VFBto the second conductor of the charging cable56, which is thus added to the charging voltage VCHGvia the isolation capacitor C2to generate the control voltage VCTRL. Therefore, because the isolation capacitor C2provides DC blocking capability, the DC feedback control voltage VFBdoes not affect the amplitude of the charging voltage VCHG. The control voltage VCTRLis thus provided to the AC adapter52, and is thus provided to the programmable AC current source54. Therefore, the programmable AC current source54can set the amplitude of the AC charging current ICHGbased on the control voltage VCTRLin a feedback manner. Particularly, an average voltage across the isolation capacitor C1in the AC adapter52can correspond to the DC feedback control voltage VFBbased on the DC blocking capability of the isolation capacitor C1. Accordingly, the programmable AC current source54can provide the AC charging current ICHGat an amplitude that corresponds to the requested amplitude as provided by the amplitude of the DC feedback control voltage VFBprovided by the charge controller60. Accordingly, the battery B1can be charged rapidly in a closed-loop manner based on the programmable AC current source54generating the AC charging current ICHGat an amplitude that is dictated by the amplitude of the battery voltage VBAT.

The battery charging system50can be implemented to charge any of a variety of electronic devices, and can implement any of a variety of different types of charging cables for the charging cable56. As described previously, the charging cable56can be implemented as a USB cable, such that existing designs for USB cables and associated connectors can be used. As an example, one or more of the pins of existing USB cable and connector designs can be left unused, or can be used for additional control purposes unrelated to charging of the battery B1. Additionally, because the battery charging system50implements charging based on an AC charging current ICHG, the polarity of the charging cable56is irrelevant. Particularly, changing the polarity of the charging cable56can change the polarity of the control voltage VCTRL, but given that the programmable AC current source54can monitor the absolute value of the control voltage VCTRL(e.g., based on the average voltage across the isolation capacitor C1corresponding to the DC feedback control voltage VFB), the polarity of the control voltage VCTRL, and thus the charging cable56, is irrelevant. Furthermore, because of the simplified two-conductor connection between the AC adapter52and the device power system58, legacy USB cables, such as a USB Type-C cable, can be used in the battery charging system50to provide backward compatibility with existing charging cables.

FIG. 3illustrates yet another example of a battery charging system100. The battery charging system100can correspond to either of the battery charging systems10and50in the respective examples ofFIGS. 1 and 2. The battery charging system100includes an AC adapter102and a device power system104. The AC adapter102can be configured substantially the same as the AC adapter52, and can thus include a programmable AC current source configured to generate an AC charging current based on a control voltage. Similarly, the device power system104can be configured substantially the same as the device power system58, and can thus be configured to convert the AC charging current to a DC charging current to charge the battery, and can generate the DC feedback control voltage that is provided back to the AC adapter via the control voltage.

In the example ofFIG. 3, the battery charging system100includes a USB-Type C cable106that interconnects the AC adapter102and the device power system104. The USB-Type C cable106can implement a connection of two conductors between the AC adapter102and the device power system104, such that the first conductor can provide the AC charging current from the AC adapter102to the device power system104and the second conductor can provide the control voltage from the device power system104to the AC adapter102. In the example ofFIG. 3, the USB-Type C cable106is demonstrated as having a coupling of an A12pin and a B1pin at each of a connector108associated with the AC adapter102and a connector110associated with the device power system104. Similarly, the USB-Type C cable106is demonstrated as having a coupling of an A1pin and a B12pin at each of the connector108and the connector110. The respective A1and B12pins and A12and B1pins can be electrically coupled (i.e., shorted) in either the respective connectors108and110or in the USB-Type C cable106itself.

As an example, the AC charging current can have a maximum amplitude of 36 volts RMS, such that the AC adapter102can deliver 32 watts per ampere RMS. For an AC resistance at 1 MHz that is four times greater than the respective DC resistance of the USB-Type C cable106, the current rating of the USB-Type C cable106can be de-rated by a factor of two. Therefore, assuming an approximately 90% power delivery efficiency, the USB-Type C cable106can be configured to deliver approximately 36 watts for a five ampere rating of the USB-Type C cable106, or to deliver approximately 21.6 watts for a three ampere rating of the USB-Type C cable106. Therefore, the USB-Type C cable106can be implemented as described herein to provide more rapid charging of a battery of a mobile device relative to typical battery charging systems without requiring a cable adapted for use with the battery charging system50, as described herein. Alternatively, a cable with a higher power rating can be used in the battery charging system50, as described herein, to provide even more rapid battery charging.

FIG. 4illustrates a method150for charging a battery (e.g., the battery20) associated with a mobile device. At152, a power voltage (e.g., the voltage VLINE) is received at an AC adapter (e.g., the AC adapter12). At154, an AC charging current (e.g., the AC charging current ICHG) is generated based on the power voltage via a programmable AC current source (e.g., the programmable AC current source14) associated with the AC adapter. The AC charging current can be provided on a first conductor of a charging cable (e.g., the charging cable16) that interconnects the AC adapter and the mobile device. At156, a control voltage (e.g., the control voltage VCTRL) is received on a second conductor of the charging cable. The control voltage can include a voltage associated with the AC charging current (e.g., the charging voltage VCHG) and a DC feedback control voltage (e.g., the DC feedback control voltage VFB). At158, an amplitude of the AC charging current is adjusted based on an amplitude of the DC feedback control voltage.

What have been described above are examples of the disclosure. It is, of course, not possible to describe every conceivable combination of components or method for purposes of describing the disclosure, but one of ordinary skill in the art will recognize that many further combinations and permutations of the disclosure are possible. Accordingly, the disclosure is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims.