SWITCHING POWER CONVERTER FOR DIRECT BATTERY CHARGING

Abstract

A direct charging method is provided that alerts a mobile device when a switching power converter is operating in a constant-current mode to alert the mobile device of an output current without the use of a secondary-side current sense resistor.

Claims

1. A method of directly charging a battery for a mobile device using a flyback converter that does not include a sense resistor in series with a secondary winding of a transformer, comprising: receiving at a secondary controller for the flyback converter over a data channel in a data interface cable, a desired output voltage command for setting a first output voltage limit and a desired output current command for setting a first output current; transmitting the desired output voltage command and the desired output current command from the secondary controller to a primary controller for the flyback converter; in the primary controller, regulating a cycling of a power switch according to a constant-voltage mode when an output voltage for the flyback converter equals the first output voltage limit; in the primary controller, regulating the cycling of the power switch according to a constant-current mode when an output current from the flyback converter equals the first output current limit; in the secondary controller, determining when the output voltage indicates that the primary controller is in the constant-current mode; and alerting the mobile device of the determination that the primary controller is in the constant-current mode.

2. The method of claim 1, further comprising: responsive to the alerting of the mobile device, receiving a revised output voltage command setting a revised output voltage limit; and regulating the power switch cycling responsive to the revised output voltage limit.

3. The method of claim 2, wherein the revised output voltage limit is greater than the first output voltage limit.

4. The method of claim 1, further comprising: digitizing the output voltage to form a digitized output voltage; and from the secondary controller, transmitting the digitized output voltage to the mobile device over the data channel in the data interface cable.

5. The method of claim 4, further comprising: responsive to the digitized output voltage being sufficiently close to the first output voltage limit, transmitting from the mobile device over the data channel in the data interface cable to the secondary controller a revised output current limit command setting a second output current limit that is less than the first output current limit; transmitting the revised output current limit command from the secondary controller to the primary controller; and regulating the cycling of the power switch according to the second output current limit.

6. The method of claim 1, wherein transmitting the desired output voltage command and the desired output current command from the secondary controller to the primary controller comprises transmitting the desired output voltage command and the desired output current command over an optoisolator.

7. The method of claim 1, wherein transmitting the desired output voltage command and the desired output current command from the secondary controller to the primary controller comprises transmitting the desired output voltage command and the desired output current command by pulsing a synchronous rectifier switch.

8. The method of claim 1, wherein the data interface cable is a Universal Serial Bus cable.

9. The method of claim 1, wherein the data interface cable is a Lightning cable.

10. A method of directly charging a battery for a mobile device using a flyback converter that does not include a sense resistor in series with a secondary winding of a transformer, comprising: receiving at a secondary controller for the flyback converter over a data channel in a data interface cable, a desired output voltage command for setting a first output voltage limit and a desired output current command for setting a first output current; transmitting the desired output voltage command and the desired output current command from the secondary controller to a primary controller for the flyback converter; in the primary controller, regulating a cycling of a power switch according to a constant-voltage mode when an output voltage for the flyback converter equals the first output voltage limit; in the primary controller, regulating the cycling of the power switch according to a constant-current mode when an output current from the flyback converter equals the first output current limit; digitizing the output voltage to form a digitized output voltage; from the secondary controller, transmitting the digitized output voltage to the mobile device over the data channel in the data interface cable; and in the mobile device, determining when the digitized output voltage indicates that the primary controller is in the constant-current mode.

11. The method of claim 10, further comprising: responsive to the digitized output voltage indicating that the primary controller is in the constant-current mode, receiving at the secondary controller a revised output voltage command setting from the mobile device, wherein the revised output command sets a revised output voltage limit; and regulating the power switch cycling responsive to the revised output voltage limit.

12. The method of claim 11, wherein the revised output voltage limit is greater than the first output voltage limit.

13. The method of claim 11, further comprising: responsive to the digitized output voltage being sufficiently close to the first output voltage limit, transmitting from the mobile device over the data channel in the data interface cable to the secondary controller a revised output current limit command setting a second output current limit that is less than the first output current limit; transmitting the revised output current limit command from the secondary controller to the primary controller; and regulating the cycling of the power switch according to the second output current limit.

14. The method of claim 10, wherein transmitting the desired output voltage command and the desired output current command from the secondary controller to the primary controller comprises transmitting the desired output voltage command and the desired output current command over an optoisolator.

15. The method of claim 10, wherein transmitting the desired output voltage command and the desired output current command from the secondary controller to the primary controller comprises transmitting the desired output voltage command and the desired output current command by pulsing a synchronous rectifier switch.

16. A flyback converter, comprising: a primary controller configured to cycle a power switch in a constant-voltage mode responsive to an output voltage equaling a first output voltage limit and to cycle the power switch in a constant-current mode responsive to an output current equaling a first output current limit; and a secondary controller configured to receive the first output voltage limit and the first output current limit from a mobile device over a data channel in a data interface cable and to transmit the first output voltage limit and the first output current limit to the primary controller, wherein the secondary controller is further configured to transmit a constant-current flag signal to the mobile device responsive to the output voltage equaling the first output voltage limit.

17. The flyback converter of claim 16, wherein the secondary controller is further configured to digitize the output voltage into a digitized output voltage and to transmit the digitized output voltage over the data channel in the data interface cable to the mobile device.

18. The flyback converter of claim 17, wherein the data interface cable is a Universal Serial Bus cable.

19. The flyback converter of claim 17, wherein the data interface cable is a Lightning cable.

20. The flyback converter of claim 17, wherein the secondary controller is further configured to receive a revised output current limit from the mobile device over the data channel in the data interface cable and to transmit the revised output current limit to the primary controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 illustrates an example battery charging system in accordance with an aspect of the disclosure.

[0015] FIG. 2 is a flow chart for a first phase of a direct battery charging method.

[0016] FIG. 3 illustrates waveforms for a direct battery charging system during the first and second phases of the direct battery charging in accordance with an aspect of the disclosure.

[0017] FIG. 4 illustrates the transition of the constant-voltage and constant-current modes of operation during the first phase of a direct battery charging in accordance with an aspect of the disclosure.

[0018] FIG. 5 illustrates the transition of the constant-voltage and constant-current modes of operation during the second phase of a direct battery charging in accordance with an aspect of the disclosure.

[0019] FIG. 6 illustrates the transition of the constant-voltage and constant-current modes of operation during the third phase of a direct battery charging in accordance with an aspect of the disclosure.

DETAILED DESCRIPTION

[0020] An efficient means of battery charging is provided in which the charging operation is controlled through current or voltage flags and a comparison system. The following discussion will be directed to a flyback converter power adapter (PA), such as a travel adapter or USB power supply, and a battery powered device (BPD), such as a phone, tablet, or USP powered device, but it will be appreciated that the resulting techniques may be widely applied to other types of PAs and BPDs without deviating from the scope of the invention.

[0021] An example charging system 100 including a flyback converter power adapter 105 and a mobile (client) device 130 is shown in FIG. 1. Flyback converter including a primary controller 120 that regulates the switching of a power switch transistor Si that has a drain connected to a primary winding T1 of a transformer that receives an input voltage V_IN. Primary controller 120 senses the drain voltage Vdrain of the power switch transistor Si to monitor an output voltage V.sub.BUS from flyback converter 105 as known in the primary-only feedback flyback converter arts. An output diode D1 prevents the secondary winding from conducting current while the primary current flows through primary winding T1. Alternatively, output diode D1 may be replaced by a synchronous rectifier switch.

[0022] A secondary controller 125 couples to data terminals such as terminals D+ and D− for a data interface cable/connector. Secondary controller 125 can thus receive a digitized output voltage limit command (Vcmd) and a digitized output current limit command (Icmd) from mobile (client) device 130. The following discussion will assume that the data interface cable is a USB cable but it will be appreciated that the direct charging disclosed herein may be practiced with other types of data interface cables such as the Lightning cable used for iPhones. The USB cable also includes an output voltage terminal and a ground (GND) terminal so that the output voltage and output current may be driven over the USB cable to mobile device 130. Secondary controller 125 includes an ADC 115 for digitizing the output voltage so that it may report the digitized output voltage to mobile device 130 over the D+ and D− data channels of the USB cable. Similarly, secondary controller 135 transmits the constant current flag over the D+ and D− data channels to mobile device 130. Secondary controller 300 transmits the desired output current limit and output voltage limit through an independent data channel 110 such as an optocoupler but it will be appreciated that primary-only data communication may be used as discussed above to transmit this data to primary controller 120.

[0023] As noted earlier, primary controller 120 may regulate the cycling of the power switch transistor S1 in a constant-current mode to provide an output current: I.sub.OUT=kcc/2*Npri/Nsec/Rs, where kcc is a coefficient for the constant current limit, Npri/Nsec is the transformer primary side to secondary side turns ratio, and Rs is the current sense resistor (not illustrated) in series with the power switch transistor S1 at the primary side. The kcc coefficient depends upon the regulation of cycling of the power switch transistor S1 such as the power switch transistor on time and also the transformer reset time. In particular, primary controller 120 will attempt to drive the output voltage Vbus from flyback converter to the desired output voltage limit such that it would operate in constant-voltage mode. But if the cycling of the power switch in striving to reach constant-voltage operation would lead to an output current that exceeds the current limit, primary controller 120 instead transitions to a constant-current operation at the desired current limit. With regard to the constant-voltage and constant-current modes of operation, secondary controller 125 will monitor the output voltage V.sub.BUS through, e.g., ADC 115 to determine whether the output voltage is sufficiently close to the desired output voltage limit. For example, secondary controller 125 may be configured to monitor whether the output voltage is greater than the difference between the desired output voltage and a guard band margin voltage (Vmargin). Should secondary controller 125 determine that the output voltage is less than this difference, it de-asserts the constant current flag to signal to mobile device 130 that flyback converter 105 is operating in a constant-current mode. Conversely, should secondary controller 125 determine that the output voltage is greater than the difference between the output voltage and Vmargin, secondary controller 125 asserts the constant current flag to signal to mobile device 130 that flyback converter 105 is operating in a constant-voltage mode. Secondary controller 125 thus does not need a sense resistor to monitor the output current from flyback converter, which advantageously increases efficiency as compared to conventional direct charging techniques.

[0024] Although the assertion of the constant current flag to signal whether operation proceeds in a constant-current or constant-voltage mode of operation is convenient, note that the inclusion of the constant current flag is optional in that mobile device 130 itself may be configured to determine whether the output voltage is sufficiently close to the desired voltage limit. Mobile device 130 may thus determine on its own whether flyback converter 105 is operating in a constant-current or a constant-voltage mode of operation in alternative embodiments. Regardless of where the constant-current or constant-voltage determination is made, mobile device 130 may then proceed to alter the output current or output voltage limits to effect the desired charging profile for its battery. Such a charging profile may occur according to the three phases discussed above. Control during these three phases will be discussed further below.

[0025] In the first phase of battery charging, the battery is discharged such that the output voltage will gradually climb from the discharged state to some maximum voltage. The mobile phone will thus successively increase the desired voltage Vcmd during the first phase. The desired output current Icmd stays constant such as at some output maximum (e.g., 4 A). For a given value of Vcmd, the flyback converter will initially be in the constant-current mode until the output voltage reaches Vcmd, whereupon constant-voltage regulation proceeds. The mobile phone reacts to the transition to constant-voltage regulation by increasing Vcmd such that the flyback converter transitions to constant-current regulation. But as charge is built up in the battery, eventually the output voltage will again reach the revised value of Vcmd, whereupon Vcmd is again increased. In this fashion, the output voltage is successively increased during the first phase of battery direct charging.

[0026] The resulting control by mobile device 130 of the desired output voltage and output current limits during the first phase of direct battery charging is summarized in the flow chart shown in FIG. 2. As shown in FIG. 2, the mobile device (BPD) in an act 210 sends a request to the secondary controller for a desired Vbus Voltage (Vcmd) and a desired Vbus current (Icmd). In an act 220, the secondary controller communicates these values to the primary controller, which begins regulating the cycling of the power switch accordingly. In an act 230, the secondary controller (or the primary controller) compares Vbus to (Vcmd−Vmargin). Vmargin is used to avoid unnecessary adjustments due to Vbus ripple or other aberrations. The value of Vmargin can be a static or dynamic value based on the predicted or observed ripples or aberration in the Vbus or other components. It will be appreciated that the determination made by act 230 may be done by the secondary controller, the mobile device, the primary controller, or any other component or combination of components that can access Vbus information. In Vbus is greater than (Vcmd−Vmargin), the secondary controller may de-assert the constant-current flag to indicate that the flyback converter is no longer operating in the constant-current mode. In response, the mobile device increases Vcmd in an act 240, whereupon the method continues again at act 210.

[0027] If the Vbus voltage is less than (Vcmd−Vmargin), then the secondary controller can assert the constant-current flag in an act 250. In a subsequent act 260, Vbus is compared to (Vcmd+Vmargin). If Vbus is less than Vcmd plus Vmargin, then the method returns to act 230. If Vbus is less than Vcmd plus Vmargin, the mobile device decreases the desired Vcmd in an act 270.

[0028] Once the Vcmd reaches a maximum amount for the first phase of direct battery charging, the direct battery charging method transitions to the second phase in which the desired output current Icmd is successively reduced. Various waveforms for system 100 during the second phase are shown in FIG. 3. A waveform 310 represents the output voltage Vbus. A waveform 340 represents the output current from the flyback converter. The constant-current flag is represented by waveform 350. Finally, Vcmd and Icmd are represented by waveforms 360 and 370, respectively. The second phase begins at time T1. At that time Vcmd equals 4.1 V whereas Icmd equals 4 A across the entire second phase (from time T1 through time T7). Since the output voltage Vbus is less than Vcmd at time T1, the regulation proceeds according to the constant-current mode of operation such that the constant-current flag is asserted at time T1. At time T2, the output voltage reaches Vcmd (in this example, Vmargin is negligible) such that the constant-current flag is de-asserted. Regulation proceeds in the constant-voltage mode of operation until time T3 whereupon the mobile device increases Vcmd to 4.2 V in response to the constant-current flag being de-asserted. Since the output voltage is less than Vcmd at time T3, regulation proceeds in the constant-current mode until time T4, at which point Vout equals Vcmd such that the constant-voltage mode resumes and the constant-current flag is de-asserted. At time T5, the mobile device reacts to the de-assertion of the constant-current flag by increasing Vcmd to 4.3 V. In this fashion, Vcmd is successively increased until Vbus reaches Vcmd equaling the maximum voltage of 4.5 V at time T7 to end the second phase.

[0029] The resulting transitions between constant-voltage and constant-current regulation during the second phase are shown in FIG. 4. Constant-current operation occurs from time T1 to time T2 whereas constant-voltage operation occurs from times T2 to T3 (Vcmd equaling 4.1 V). In response to the increase in Vcmd to 4.2 V at time T3, the flyback converter pushes the regulation back into the constant-current mode until time T4. From times T4 to time T5, the regulation proceeds in constant-voltage mode with Vbus equaling 4.2 V. But Vcmd is increased to 4.3 V at time T5 so that constant-current regulation is eventually reached until time T6 at which point Vbus equals 4.3 V. Several more rounds of increasing Vcmd are then performed until the maximum voltage of 4.5 V is reached at time T7.

[0030] Referring again to FIG. 3, phase two operation proceeds from time T7 until time T10. At time T7, the mobile device reduces Vcmd slightly from 4.5 V while reducing Icmd more significantly from 4 A to 3.5 A. Given the reduction in Icmd, regulation proceeds in the constant-current mode until time T8, whereupon Vbus equals Vcmd. The mobile device again reduces Vcmd slightly whereas Icmd is reduced more greatly at time T8 from 3.5 A to 3 A. The mobile device continues to drop Icmd at time T9 until a minimum output current such as 2 A is reached at time T10. Since regulation is maintained in the constant-current mode across the second phase operation, the constant-current flag is asserted from time T7 to time T10. Phase 3 operation then proceeds as discussed further below.

[0031] The resulting transitions between constant-current and constant-voltage operation for the second phase are shown in FIG. 5. At time T7, Icmd is reduced from 4 A to 3.5 A and Vcmd reduced from 4.5 V to 4.475 V. Regulation then proceeds in the constant-current mode until time T8, whereupon Vbus equals Vcmd. The mobile device reacts to the increase in Vbus at time T8 by reducing Icmd to 3 A and reducing Vcmd to 4.45. Operation then proceeds in the constant-current mode until Vbus reaches Vcmd at time T9. The mobile device reacts to the increase in Vbus at time T9 by reducing Vcmd to 4.425 and Icmd to 2.5 A. Operation then proceeds in the constant-current mode until Vbus reaches Vcmd at time T10, whereupon phase 3 operation begins.

[0032] Phase 3 operation proceeds in a constant voltage mode during which time the output current continues to drop to maintain the constant-voltage regulation. The Icmd and Vcmd values are as set at the end of the second phase operation and need not be changed by the mobile device during phase 3 operation. The resulting constant-voltage/constant-current transition point is shown in FIG. 6. The output current continues to decline from 2 A at time T10 until the battery is fully charged and the end of the direct battery charging procedure is reached. The output voltage stays constant such as at 4.4 V during this final phase.

[0033] It will be appreciated that a constant-voltage flag could also be used in lieu of the constant-current flag. Such flags would be the inverse of each other. As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.