PATENT DOCUMENT

Publication Number: US-8687392-B2
Application Number: US-201213424033-A
Country: US
Kind Code: B2

Title: Power converter with automatic mode switching

Abstract:
A power converter is provided that has an alternating-current (AC) to direct-current (DC) switched-mode power converter circuit that converts alternating-current power into direct-current power for powering an attached electronic device. Power can be conserved by automatically placing the power converter circuit in a low-power standby mode of operation whenever the electronic device is detached from the power converter. A monitoring circuit can be powered by a capacitor or other energy storage element while the power converter is operating in the standby mode. If the monitoring circuit detects an output voltage change that is indicative of attachment of the electronic device or if the storage element needs to be replenished, the monitoring circuit can place the power converter circuit in an active mode of operation.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 an energy storage element coupled to an output line; 
 a power converter circuit that is operable in a normal mode in which a direct-current voltage is produced on the output line from an alternating-current voltage and that is operable in a standby mode in which the direct-current voltage is not produced; 
 circuitry coupled to the output line that is powered by power received from the power converter circuit during the normal mode; 
 monitor circuitry operable to monitor a voltage of the output line and operable to control the power converter circuit based at least partly on the monitored voltages; 
 a voltage regulator that receives an energy storage element voltage from the energy storage element and that provides a modified version of the energy storage element voltage on a voltage regulator output during the standby mode; and 
 a path that electrically couples the voltage regulator output to the output line. 
 
     
     
       2. The electronic device defined in  claim 1  further comprising:
 a switch coupled to the energy storage element, wherein the monitor circuitry is configured to control the switch based at least partly on the monitored voltage. 
 
     
     
       3. The electronic device defined in  claim 2  wherein the switch is interposed between the energy storage element and the circuitry. 
     
     
       4. The electronic device defined in  claim 3  wherein the switch is interposed between the power converter circuit and the circuitry. 
     
     
       5. The electronic device defined in  claim 4  wherein the monitor circuitry is further operable to control the switch to selectively disconnect the circuitry from the power converter circuit based at least partly on the monitored voltage. 
     
     
       6. The electronic device defined in  claim 1  wherein the circuitry includes at least one user interface component operable to monitor user activity. 
     
     
       7. The electronic device defined in  claim 6  wherein the circuitry is configured to modify the voltage of the output line based at least partly on the monitored user activity. 
     
     
       8. The electronic device defined in  claim 7  wherein the at least one user interface component comprises an infrared receiver. 
     
     
       9. The electronic device defined in  claim 7  wherein the at least one user interface component comprises a radio-frequency receiver. 
     
     
       10. The electronic device defined in  claim 1  wherein the energy storage element is configured to provide power to the monitor circuitry during the standby mode. 
     
     
       11. The electronic device defined in  claim 10  wherein the monitor circuitry is configured to periodically control the power converter circuit to replenish the energy storage element during the standby mode. 
     
     
       12. The electronic device defined in  claim 6  wherein the at least one user interface component includes a component selected from the group consisting of: a touch screen, a touch pad, a mouse, a key, a button, infrared receiver circuitry, radio-frequency wireless communications circuitry, processing and storage circuitry, and a sensor. 
     
     
       13. An electronic device, comprising:
 a first power supply circuit that produces a direct-current voltage from an alternating-current voltage, wherein the first power supply circuit is operable in an active mode in which the direct-current voltage is being produced and is further operable in a standby mode in which the direct-current voltage is not produced; 
 an energy storage element that produces an energy storage element voltage; and 
 circuitry operable to receive the direct-current voltage from the first power supply circuit during the active mode and operable to receive the energy storage element voltage from the energy storage element during the standby mode, wherein the circuitry is further operable to monitor user activity and control the first power supply circuit based at least partly on the monitored user activity, and wherein the circuitry is configured to determine when an output voltage of the energy storage element falls below a predetermined threshold and is further configured to wake up a second power supply circuit to replenish the energy storage element without waking up the first power supply circuit. 
 
     
     
       14. The electronic device defined in  claim 13  wherein the circuitry comprises:
 infrared receiver circuitry operable to monitor user activity by receiving infrared signals that identify whether the first power supply circuit should be operated in the active mode or the standby mode. 
 
     
     
       15. The electronic device defined in  claim 13  wherein the circuitry comprises:
 radio-frequency receiver circuitry operable to monitor user activity by receiving radio-frequency signals that identify whether the first power supply circuit should be operated in the active mode or the standby mode. 
 
     
     
       16. The electronic device defined in  claim 13  wherein the circuitry comprises:
 a device circuit operable to receive user input and produce a corresponding output signal on a communications path; and 
 a monitor circuit coupled to the communications path, wherein the monitor circuit is operable to receive the output signal over the communications path and further operable to control the first power supply circuit based on the received output signal. 
 
     
     
       17. An electronic device, comprising:
 a first power converter circuit configured to convert alternating current power to direct current power; 
 a second power converter circuit configured to convert alternating current power to direct current power; 
 an energy storage element; and 
 circuitry operable to:
 receive an energy storage element voltage from the energy storage element when the first and second power converter circuits are placed in a standby state to conserve power; 
 monitor user activity; and 
 control the first and second power converter circuits based at least partly on the monitored user activity, 
 
 wherein the circuitry is configured to determine when the energy storage element is depleted and is further configured to wake up the second power converter circuit to replenish the energy storage element without waking up the first power converter circuit. 
 
     
     
       18. The electronic device defined in  claim 17 , wherein the circuitry comprises infrared receiver circuitry operable to receive user input, wherein the circuitry is further operable to control the first and second power converter circuits based at least partly on the user input received by the infrared receiver circuitry.

Description:
This patent application is a continuation of patent application Ser. No. 12/370,488, filed Feb. 12, 2009 now U.S. Pat. No. 8,164,932, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates to electronic devices and power converter circuits for electronic devices. 
     Alternating current (AC) power is typically supplied from wall outlets and is sometimes referred to as line power. Electronic devices include circuitry that runs from direct current (DC) power. Power converter circuitry is used to convert AC power to DC power. The DC power that is created in this way may be used to power an electronic device. The DC power that is created may also be used to charge a battery in an electronic device. 
     In some applications, AC to DC power converter circuitry may be incorporated into an electronic device. For example, desktop computers often include AC to DC power converter circuitry in the form of computer power supply units. A computer power supply unit has a socket that receives an AC power cord. With this type of arrangement, the AC power cord may be plugged directly into the rear of the computer to supply AC power without using an external power converter. 
     Although desktop computers are large enough to accommodate internal power supplies, other devices such as handheld electronic devices and portable computers are not. As a result, typical handheld electronic devices and laptop computers require the use of external power converters. When untethered from the power converter, a handheld electronic device or portable computer may be powered by an internal battery. When AC line power is available, the power converter is used to convert AC power into DC power for the electronic device. 
     Compact AC-DC power converter designs are typically based on switched-mode power supply architectures. Switched-mode power converters contain switches such as transistor-based switches that work in conjunction with energy storage components such as inductive and capacitive elements to regulate the production of DC power from an AC source. A feedback path may be used to tap into the converter output and thereby ensure that a desired DC voltage level is produced under varying loads. 
     High power converter efficiency is desirable for conserving power. High power conversion efficiency can be obtained by using efficient converter topologies and low-loss parts. Even when an optimal design is used, however, there are residual power losses when operating a power converter. These residual losses are associated with leakage currents and other parasitics that arise from running the switched-mode circuitry of the converter and lead to the consumption of power by the power converter even when the power converter is not being actively used to power an electronic device. Power consumption when the power converter is not being used to power an electronic device represents a source of undesirable power loss that can be reduced without adversely affecting converter functionality. 
     SUMMARY 
     A power converter may be provided that includes an energy storage circuit. The power converter may receive an input signal such as a line power signal and may produce a corresponding output signal such as a power signal for a device or other circuitry. The power converter may be placed in standby mode to conserve power. In standby mode, the energy storage circuit may be used to power circuitry that can wake the power converter from standby when appropriate. The power converter circuit can be provided as part of a stand-alone power adapter or may be incorporated into other electronic devices. 
     With one suitable arrangement, the power converter may be a power converter circuit such as an alternating-current (AC) to direct-current (DC) switched mode power converter circuit. The power converter circuit may convert AC line power into DC power for powering an attached electronic device. For example, the power converter may be used for powering an electronic device such as a cellular telephone, portable computer, or music player. 
     The power converter circuit may have a switch that is modulated to control power flow. When the switch is turned off, the power converter circuit is essentially shut down and will not produce a DC power at its output. In this state, which is sometimes referred to as a standby mode or sleep mode, power consumption by the power converter is minimized. When it is desired to power an attached electronic device, the power converter circuit may operate in an active mode in which the switch is actively modulated to produce a desired output signal (e.g., the DC output voltage). 
     The power converter circuit may provide its output to an output line through switching circuitry. During normal operation, a monitor circuit places the switching circuitry in a closed state in which the power converter circuit is coupled to the output line and produces a DC output voltage for powering the electronic device. Periodically, the monitor may open the switching circuitry to isolate the power converter circuit from the output line. The behavior of the voltage on the output line can be monitored by the monitor. In the presence of a load that draws power, the output line voltage will tend to sag. When driven by an internal boosting circuit with no load present, the output line voltage may rise (or may at least not fall past a given threshold). If the voltage on the output line rises (or does not fall past the given threshold), the monitor can conclude that the electronic device is detached from the power converter. If the voltage on the output line falls (or falls past the given threshold), the monitor can conclude that the electronic device is attached to the power converter. 
     The power converter may include an energy storage element such as a capacitor or battery. When the power converter circuit is operating in standby mode, the monitor can draw power from the energy storage element. This allows the monitor to actively monitor the state of the output line to automatically determine when an electronic device is reattached to the power converter. The monitor may also monitor the status of the energy storage element. If the energy storage element becomes depleted, the monitor can direct the power converter circuit to momentarily transition from the standby mode of operation to the active mode of operation to replenish the energy storage element. If a drop in the output line voltage is detected that is indicative of reattachment of the electronic device to the power converter, the monitor may activate the power converter circuit so that the electronic device is powered. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of a system including a power converter and an electronic device in accordance with an embodiment of the present invention. 
         FIG. 2  is a circuit diagram showing illustrative components that may be used for a power converter of the type shown in the diagram of in  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 3  is a graph showing how the output voltage from a power converter of the type shown in  FIG. 2  may evolve when an electronic device is detached from the power converter in accordance with an embodiment of the present invention. 
         FIG. 4  is a graph showing how the voltage on an energy storage element in a power converter of the type shown in  FIG. 2  may evolve during standby mode operations and energy replenishment operations in accordance with an embodiment of the present invention. 
         FIG. 5  is a graph showing how the output voltage from a power converter of the type shown in  FIG. 2  may evolve when an electronic device is attached to the power converter in accordance with an embodiment of the present invention. 
         FIG. 6  is a graph showing how the output voltage from a power converter of the type shown in  FIG. 2  may evolve during a monitoring operation as an electronic device that is being powered by the power converter remains attached to the power converter in accordance with an embodiment of the present invention. 
         FIG. 7  is a diagram showing illustrative operating modes and operations involved in transitioning between operating modes in a power converter of the type shown in  FIG. 2  in accordance with an embodiment of the present invention. 
         FIG. 8  is a diagram of an electronic device showing how a monitor circuit may be powered by an energy storage circuit to detect power supply changes in a power supply line within the electronic device in accordance with an embodiment of the present invention. 
         FIG. 9  is a diagram of an electronic device showing how a monitor circuit that is powered by an energy storage circuit may be used to wake up a power supply in the electronic device that has been placed in standby mode in accordance with an embodiment of the present invention. 
         FIG. 10  is a diagram of an electronic device having first and second power supplies showing how a monitor circuit that is powered by an energy storage circuit may be used in controlling the first and second power supplies in accordance with an embodiment of the present invention. 
         FIG. 11  is a diagram of an illustrative power adapter housing configuration that may be used for power adapter circuitry of the type shown in  FIG. 1  in accordance with an embodiment of the present invention. 
         FIG. 12  is a diagram of an illustrative power adapter housing configuration that may be used for power adapter circuitry of the type shown in  FIG. 1  and that may have a magnetic attachment mechanism in accordance with an embodiment of the present invention. 
         FIG. 13  is a diagram showing how a power converter circuit output capacitor may be used as an energy storage device to power a monitor circuit in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Power converters, which are sometimes referred to as power adapters, are used to convert power levels and types. For example, a power converter may be used to boost or reduce a direct-current (DC) power level. Power converters may also be used to convert alternating current (AC) power into DC power. Power converters that are used in converting AC power to DC power are sometimes described herein as an example. In general, however, power converter circuitry may include circuitry for transforming any suitable input signal (e.g., AC or DC currents and voltages) into any suitable output signal (e.g., boosted, reduced, or otherwise transformed AC or DC currents and voltages). The use of power converters such as AC-to-DC power converters that produce regulated DC output voltages from AC input signals is merely illustrative. 
     In a typical scenario, a power converter may be plugged into a source of AC line power such as a wall outlet. The AC power source may provide power at 120 volts or 240 volts (as examples). Circuitry in the power converter may convert the AC line power that is received into DC power. For example, an AC to DC power converter may receive AC line power at an input and may supply DC power at a corresponding output. The output voltage level may be 12 volts, 5 volts, or any other suitable DC output level. 
     The circuitry in the power converter may be based on a switched mode power supply architecture. Switched mode power supplies use switches such as metal-oxide-semiconductor power transistors and associated control schemes such as pulse-width modulation control schemes or frequency modulation control schemes to implement power conversion functions in relatively compact circuits. When the switching circuitry has a first configuration, power is transferred from a power source to a storage element such as an inductor (e.g., a transformer) or a capacitor. When the switching circuitry has a second configuration, power is released from the storage element into a load. Feedback may be used to regulate the power transfer operation and thereby ensure that the output voltage is maintained at a desired level. Examples of switched mode power supply topologies that may be used in a power converter include buck converters, boost converters, flyback converters, etc. 
     With one suitable arrangement, which is described herein as an example, an AC to DC power converter may be implemented using a voltage rectifier and flyback converter. The voltage rectifier converts AC line power into DC power at a relatively high voltage level. The flyback converter portion of the power converter steps down the DC power at the output of the rectifier circuit to 12 volts, 5 volts, or other suitably low level for operating circuitry in an electronic device. If desired, other power converter architectures may be used. The use of a switched mode power converter arrangement that is based on a flyback converter design is described herein as an example. 
     An AC to DC power converter may supply DC power to any suitable electronic device. Examples of an electronic device that may receive DC power from an AC to DC power converter include a handheld computer, a miniature or wearable device, a portable computer, a desktop computer, a router, an access point, a backup storage device with wireless communications capabilities, a mobile telephone, a music player, a remote control, a global positioning system device, and a device that combines the functions of one or more of these devices. With one suitable arrangement, which is sometimes described herein as an example, the electronic device that receives power from the AC to DC converter is a compact portable device such as a handheld electronic device (e.g., a mobile telephone or music player). This is, however, merely illustrative. The AC to DC power converter may be operated in conjunction with any suitable electronic device. 
     An illustrative system environment in which a power converter may provide power to an electronic device is shown in  FIG. 1 . As shown in  FIG. 1 , system  8  may include a source of AC power such as AC power source  14 , a power converter such as AC to DC power converter  12 , and an electronic device such as electronic device  10 . 
     AC power source  14  may be, for example, a standard wall outlet that supplies AC line power via a power cord. Wall outlet power is typically delivered at AC voltages of about 110 volts to 240 volts. 
     Power converter  12  may include a power converter circuit such as AC-DC power converter circuit  122 . AC-DC power converter circuit  122  may be based on a switched-mode power supply design such as a flyback converter or other suitable power converter topology. 
     Electronic device  10  may have a battery for use in powering device  10  when unattached to power converter  12 . When power converter  12  is plugged into AC power source  14  and when electronic device  10  is connected to power converter  12 , power converter  12  can transform AC power that is received from AC power source  14  into DC power for device  10 . 
     If desired, connectors may be provided at the input and/or output of power converter  12 . For example, device  10  may have a universal serial bus (USB) port into which a USB cable may be plugged. The USB cable may be used to convey DC power between power converter  12  and electronic device  10 . For example, the USB cable or other cable may contain a first line such as positive power supply line  72  that is used to convey a positive DC voltage at 12 volts, 5 volts, or other suitable positive DC voltage level from converter  12  to device  10 . This DC voltage level is sometimes referred to as Vbus and line  73  of converter  12  is sometimes referred to as a power supply bus or output line. The USB cable or other cable may also have a second line such as ground line  74  that is used to convey a ground voltage at 0 volts or other suitable ground voltage level to device  10 . A cable such as a USB cable may also contain data lines that may optionally be used to convey information between device  10  and converter  12 . 
     When connected to power converter  12 , electronic device  10  may receive DC power through the power pins of the USB connector and cable (as an example). The use of a USB connector to connect power converter  12  and electronic device  10  is, however, merely illustrative. Any suitable plugs, jacks, ports, pins, other connectors, or a hardwired connection may be used to interconnect power converter  12  and electronic device  10  if desired. Similarly, a hardwired connection or a suitable plug, jack, port, pin structure, or other connector may be used to connect power converter  12  to power source  14 . 
     AC-DC power converter circuit  122  may convert AC power from AC source  14  to DC power on output paths  64  and  70 . Path  64  may be a positive power supply line that is coupled to converter output line  73  via switch SW 2 . Path  70  may be a ground power supply line that is coupled to ground output  75  of converter  12  and ground line  74  in the cable or other path connecting converter  12  to device  10 . Switching circuitry such as switch SW 2  may be based on any suitable electrical components that can control the flow of DC power from the output of AC-DC power converter circuit  122  to the power supply input lines associated with electronic device (e.g., the inputs of device  10  that are connected to power supply lines  72  and  74 ). For example, switching circuitry SW 2  may be implemented using one or more transistors such as one or more power field-effect transistors (power FETs). During normal operation in which an electronic device such as electronic device  10  is connected to power converter  12 , power converter  12  may use AC-DC power converter circuit  122  to supply a DC power supply voltage on lines  64  and  70 . Switching circuitry SW 2  will generally be closed during normal operation, so line  64  will be shorted to output line  73 . This allows the DC power supply voltages at the output of AC-DC power converter circuit  122  to be provided to electronic device via paths  72  and  74 . 
     AC-DC power converter circuit  122  may contain control circuitry for controlling internal switching circuits. The control circuitry may be responsive to feedback signals. For example, a feedback path may be used to supply AC-DC power converter circuit  122  with information on the current level of voltage Vbus on output line  73 . In response to this feedback information, the control circuitry in AC-DC power converter circuit  122  can make real-time adjustments to the amount of DC voltage that is being supplied to the output of AC-DC power converter circuit. For example, if the DC voltage on output  64  has a nominal value Vsec of 5 volts and feedback indicates that the voltage has undesirably risen to 5.05 volts, the control circuitry in AC-DC power converter circuit  122  can make adjustments to lower the DC output voltage back to the nominal value (Vsec). 
     Power converter  12  may contain an energy storage circuit  50 . Energy storage circuit  50  (sometimes also referred to as an energy storage element) may be based on any suitable circuitry for storing energy. As an example, energy storage circuit  50  may include one or more batteries, capacitors, etc. During operation of power converter  12  when AC-DC power converter circuit  122  is supplying power to output path  64 , a path such as path  66  may be used to route power to energy storage circuit  50 . The power that is routed to energy storage circuit  50  in this way may be used to replenish the battery, capacitor or other energy storage components in circuit  50 . In the example of  FIG. 1 , energy storage circuit  50  is coupled to AC-DC power converter circuit  122  by paths  64  and  66 . This is, however, merely illustrative. Any suitable routing paths may be used to supply replenishing power from AC-DC power converter circuit  122  to energy storage circuit  50  if desired. 
     As shown in  FIG. 1 , power converter  12  may include monitoring circuitry such as monitor  54 . Monitor  54  may monitor the status of power converter  12  using paths such as paths  66  and  60 . When appropriate, monitor  54  may provide control signals to AC-DC power converter circuit  122  using paths such as path  76 . The control signals may be used to place AC-DC power converter circuit in an appropriate operating mode. In general, any suitable number of operating modes may be supported by AC-DC power converter circuit  122  if desired. 
     With one suitable arrangement, which is sometimes described herein as an example, AC-DC power converter circuit  122  may be placed in an active mode and a standby mode. In the active mode, which is sometimes also referred to as a high-power mode or normal operating mode, AC-DC power converter  122  is on and supplies DC output power for replenishing energy storage circuit  50  and for powering electronic device  10 . In the standby mode, which is sometimes referred to as a sleep mode or low-power mode, AC-DC power converter circuit  122  is placed in a state in which little or no power is consumed by AC-DC power converter circuit  122  (i.e., AC-DC power converter circuit  122  is turned off by inhibiting modulation of its switched-mode power supply switches). If desired, AC-DC power converter circuit  122  may have multiple lower power states (e.g., a partly off state and a fully-off state). Arrangements in which AC-DC power converter  122  is placed in either a standby state or an active state are sometimes described herein as an example. This is, however, merely illustrative. Power converter  12  may, in general, support any suitable number of operating modes (e.g., a fully-on mode, a partly-on mode, a sleep mode, a deep sleep mode, etc.). 
     When AC-DC power converter circuit  122  is in standby mode, AC-DC power converter circuit  122  is off and allows output  64  to float. In this situation, the power that has been stored in energy storage circuit  50  may be delivered to path  66  from within energy storage circuit  50 . For example, if energy storage circuit  50  contains a battery or a capacitor, the battery or capacitor may be used to supply a battery or capacitor voltage to path  66 . The voltage supplied by energy storage circuit  50  may be supplied at the same voltage level as the nominal output voltage level (Vsec) that AC-DC power converter circuit  122  supplies to path  64  when AC-DC power converter circuit  122  is in active mode. 
     Voltage regulator  66  may receive the voltage supplied by energy storage circuit  50  via path  66  on its input IN and may supply a corresponding output voltage to output path  58  via its output OUT. In the absence of a load on output line  73 , the voltage that voltage regulator  52  supplies to path  58  may be elevated with respect to Vsec (i.e., the voltage supplied by voltage regulator  52  to path  58  during standby operations may be equal to an elevated voltage Vaux that is larger than Vsec). If, for example, Vsec is 5.0 volts (as an example), Vaux may be 5.1 volts (as an example). 
     Output line  58  may be coupled to output line  73  and path  72  by path  56 . During standby mode, monitor  54  may supply a switch control signal to switching circuitry SW 2  via a path such as path  62 . The control signal may place 
     SW 2  in an open mode in which lines  64  and  73  are electrically disconnected from each other. Disconnecting output line  73  from path  64  isolates output  73  from AC-DC power converter circuit  122  and energy storage circuit  50 . The voltage that output line  73  assumes following the opening of switching circuitry SW 2  by monitor  54  depends on the status of electronic device  10 . 
     If electronic device  10  is disconnected from power converter  12  when switching circuitry SW 2  opens, voltage regulator  52  will supply elevated voltage Vaux to output line  73  via paths  58  and  56 , thereby driving Vbus to Vaux. If electronic device  10  is connected to power converter  12  when monitor  54  opens switching circuitry SW 2 , electronic device  10  will operate as a load and will draw power from voltage regulator output OUT via lines  58  and  56 . Voltage regulator  52  may contain a current limiting circuit that ensures that voltage regulator  52  will only be able to supply a relatively modest amount of current to electronic device  10 . As a result, the power draw from electronic device  10  will pull Vbus low. 
     Monitor  54  may determine the attachment status of electronic device  10  by monitoring the voltage Vbus on output line  73  via paths  56  and  60 . If the monitor detects a rise in voltage Vbus when switching circuitry SW 2  is opened, monitor  54  can conclude that electronic device  10  is currently detached from power converter  12 . If monitor  54  detects a drop in voltage Vbus when switching circuitry SW 2  is opened, monitor  54  can conclude that electronic device  10  is currently attached to power converter  12 . Whenever monitor  54  determines that electronic device  10  is attached to power converter  12 , monitor  54  may place AC-DC power converter circuit  122  in active mode to supply device  10  with power. If the presence of electronic device  10  is not detected, monitor may leave AC-DC power converter circuit in standby mode to conserve power. If monitor  54  detects that energy storage circuit  50  has become depleted due to prolonged operation in standby mode, monitor  54  may awaken AC-DC power converter circuit  122  momentarily to replenish energy storage circuit  50 . 
     Power converter  12  of  FIG. 1  may be implemented using any suitable circuits. Illustrative circuitry that may be used in implementing power converter  12  is shown in  FIG. 2 . In the example of  FIG. 2 , power converter circuit  122  has been formed using a flyback switched-mode power supply design. This is, however, merely illustrative. Any suitable power converter circuitry may be used for AC-DC power converter circuit  122  if desired. 
     As shown in  FIG. 2 , AC source  14  may be coupled to power converter  12  at terminals L and N. AC power from terminals L and N may be supplied to paths  20  and  22 . 
     Power converter  12  may have rectifier circuitry  16 . Diodes  18  may convert AC voltages on paths  20  and  22  to rectified (positive) signals across lines  24  and  26 . The AC voltage on paths  20  and  22  may be sinusoidal and the output of rectifier circuit  16  may be a rectified sinusoid. To smooth out the raw rectified output from diodes  18 , power converter  12  may include capacitor  28 . Capacitor  28 , which may be considered to be part of rectifier  16 , converts the rectified version of the AC signal from source  14  into a DC voltage on node  30  with a reduced amount of AC ripple. 
     AC-DC power converter circuit  122  may include a power converter control circuit such as converter control circuit  38 . Ground line  56  may be used to connect converter control circuit to ground path  24 . Positive power supply voltage Vb may be supplied to converter control circuit  38  at input  84 . Input  84  may be provided with voltage Vb by tapping power supply line  26  using bleed circuit  82 . Bleed circuit  82  may contain current limiting components such as one or more resistors. 
     Transformer  32  may have an input connected to the output of rectifier  16  and an output connected to diode  40  and capacitor  42 . Transformer  32  may have a turn ratio such as a 10:1 or 20:1 turn ratio. Switching circuitry SW 1  such as a bipolar or metal-oxide-semiconductor power transistor may be used to regulate the current Ip that flows through the primary side of transformer  32 . Switch SW 1  may receive a control signal on control input  36  from converter control circuit  38 . The control signal may have a frequency of about 20 kHz to 100 kHz (as an example). Control circuit  38  may produce the control signal on line  36  to regulate the flow of power through converter  12 . When power converter  12  is operated in active mode, the control signal is active and is changed as needed to regulate the magnitude of voltage Vbus. When power converter  12  is in standby mode, the control signal is inactive (i.e., there is no time-varying control signal present on line  36 ). This reduces power consumption in power converter  12  that would otherwise arise from the operation of switching circuitry SW 1 , even in the absence of a connected load on output line  73 . Standby power consumption can be further reduced by opening optional switching circuitry such as switches SW 3  and SW 4  to reduce leakage currents (e.g., using control signals from converter control circuit  38  and/or from monitor  54 ). 
     The control signal that is provided to switching circuitry SW 1  on line  36  may be a signal whose frequency is adjusted to control the amount of power that flows through the converter or may be a signal such as a pulse width modulation (PWM) signal whose duty cycle is adjusted to control the amount of power that flows through the converter in accordance with a pulse width modulation scheme. 
     With a typical PWM scheme, the control signal on line  36  may have a high value when it is desired to turn switch SW 1  on to permit current Ip to flow and may have a low value when it is desired to turn switch SW 1  off to prevent current Ip from flowing. The control signal on line  36  may, for example, be a square wave PWM signal whose duty cycle may be regulated by control circuit  38  to adjust the magnitude of Vbus on output  73 . If desired, a frequency modulation scheme may be used. In a frequency modulation scheme, the control signal on line  36  may be a square wave or other control signal whose frequency is regulated by control circuit  38  to adjust the magnitude of voltage Vbus. The use of PWM control signals in power converters such as power converter  12  is sometimes described herein as an example. The use of PWM control signals is, however, merely illustrative. Any suitable type of control signal may be used to control power flow in converter  12  if desired. 
     When control circuit  38  applies a control signal such as a PWM control signal to switch SW 1 , the current Is at the secondary side of transformer  32  will have a frequency equal to that of the control signal (e.g., about 20 kHz to 100 kHz). Diode  40  and capacitor  42  convert this AC signal into a DC voltage at node  44 . This voltage is provided to line  64  and represents the output of AC-DC power converter circuit  122  of  FIG. 1 . The nominal power supply output voltage on line  64 , which is sometimes referred to herein as Vsec, may be, for example, 12 volts, 5 volts, or other suitable voltage. When electronic device  10  is connected to output line  73  during active mode, the voltage that is produced at output  64  may be routed to electronic device  10  through switching circuitry SW 2 , output  73 , and path  72  to power the circuitry of electronic device  10 . 
     Power converter  12  may be controlled using an open-loop control scheme. With this type of arrangement, power converter  12  can apply a predetermined PWM signal, frequency modulation signal, or other control signal to switching circuitry SW 1  to produce a desired output level on output  64  and output line  73 . If desired, a closed-loop control scheme may be used by providing a feedback path FB such as feedback path formed from lines  48  and  49 . Using lines  48  and  49 , control circuit  38  can receive feedback on the current voltage level across nodes  44  and  46  (i.e., the output voltage on line  64 ). If the currently monitored value of the output voltage on node  44  is below a desired target level (i.e., below the desired Vsec level), the duty cycle of the PWM signal or, in a frequency modulation scheme, the frequency of the control signal can be increased to increase the output voltage accordingly. If control circuit  38  determines that the output voltage on node  44  and output  64  of AC-DC power converter circuit  122  is too high, the duty cycle of the PWM signal or the frequency of the control signal can be decreased to reduce the output voltage towards its desired target level. 
     Circuitry such as converter control circuit  38  may be located on the primary side of transformer  32 . Circuitry such as monitor circuitry  54 , energy storage element  50 , switching circuitry SW 2 , and voltage regulator  52  may be located on the secondary side of transformer  32 . If desired, an isolation stage such as isolation stage  51  may be included in feedback path FB to help electrically isolate circuitry on the primary and secondary sides of transformer  32 . Similarly, an isolation stage such as isolation stage  78  may be included in control path  76  between monitor  54  and converter control circuit  38 . Isolation stages  51  and  78  may be formed from signal transformers, optical isolation devices, etc. 
     As shown in  FIG. 2 , energy storage circuit  50  may be formed from an energy storage element such as capacitor  80 . Capacitor  80  may be coupled between path  66  and ground (e.g., node  46 ). During standby operations, capacitor  80  may be used to power monitor  54  and voltage regulator  52 . Monitor  54  can monitor the output voltage from capacitor  80  on path  66  to determine when capacitor  80  has become depleted enough to warrant replenishment. When replenishment of the energy of capacitor  80  is desired, monitor  54  can issue a wake-up control signal to converter control circuit  38  via control path  76 . In response, converter control circuit  38  can transition to active mode by resuming the generation of control signals on control line  36 . This will lead to the production of a DC output voltage on line  64  that can be routed to capacitor  80  via path  66  to recharge capacitor  80 . Battery-based energy storage elements may also be recharged in this way when they become depleted. An energy storage element  50  that is based on a battery may have, for example, a charger circuit connected between path  66  and the battery. 
     Voltage regulator circuit  52  may be formed from a DC-DC power converter such as a DC-DC boost converter  52 A and a current limiting circuit such as current limiting circuit  52 B. If desired, the current limiting capabilities of current limiting circuit  52 B may be combined with the voltage regulating capabilities of power converter circuit  52 A. In the example of  FIG. 2 , voltage regulation and current limiting functions have been implemented using separate circuits. This is merely illustrative. Circuits such as power converter  52 A and  52 B may be formed from one, two, or more than two integrated circuits and may, if desired, include discrete components. 
     Power converter  52 A may be a switched-mode power supply such as a boost circuit formed from control circuitry (such as control circuit  38 ), storage elements (capacitors and/or inductors), and other components (e.g., diodes). Electrical components such as these may be implemented as part of a single integrated circuit. During operation, boost converter  52 A may receive power (e.g., a DC voltage Vstore from capacitor  80 ) on input IN and may provide a corresponding output voltage on output OUT. The output voltage on output OUT of power converter  52 A may be lower or higher than the voltage Vstore. In the example of  FIG. 2 , converter  52 A is a boost converter that produces a nominal output voltage Vaux on output OUT that is greater than the nominal output voltage Vsec produced at output  64  of power converter circuit  122 . If, for example, Vsec is 5.0 volts, Vaux may be 5.1 volts (as an example). The voltage Vstore may range from 5.0 volts when capacitor  80  is fully charged to a lower value (e.g., a voltage in the range of about 1-4.5 volts) as capacitor  80  becomes depleted. 
     Current limiting circuit  52 B may be implemented using one or more resistors or other suitable circuitry for limiting the maximum amount of current that may be drawn from power converter  52 A when a load is connected to output line  73 . 
     When power converter circuit  122  is in standby mode, switch SW 2  will be open. In the absence of a load on output line  73 , current limiting circuit  52 B can pass the voltage on output OUT of boost converter  52 A to line  58  with negligible change in magnitude. In this situation, if the nominal output voltage from boost converter  52 A is Vaux, the DC voltage Vbus on output line  73  will rise to Vaux. 
     When a load such as electronic device  10  is connected to power converter  12 , the voltage Vbus on output line  73  will be pulled low. Boost converter  52 A will not be able to maintain Vbus at Vaux in this situation, because current limiting circuit  52 B serves to limit the amount of current that can be supplied to device  10 . This causes voltage Vbus to sag under load. 
     Monitor  54  can therefore monitor the attachment status of electronic device  10  by measuring the voltage Vbus and observing changes that take place in Vbus while controlling switching circuitry SW 2 . 
       FIG. 3  shows how the voltage Vbus on output line  73  may evolve when a user detaches electronic device from power converter  12 . At times before t 0 , electronic device  10  is attached to power converter  12  and receives DC power over lines  72  and  74 . Power converter circuitry  122  is in its active mode and supplies a DC output voltage at nominal output voltage Vsec on output  64 . Switching circuitry SW 2  is closed during active mode, so the voltage Vsec on output  64  of power converter circuit  122  is passed to power converter output line  73 . The voltage Vbus on line  73  is therefore equal to Vsec at times before t 0 . At time t 0 , the user detaches electronic device  10  from output line  73 . Because output line  73  is connected to output  64 , which is supplying voltage Vsec, voltage Vbus remains at voltage Vsec. At time t 1 , monitor  54  opens switching circuitry SW 2  to isolate output line  73  from power converter circuit  122 . Monitor  54  may open switching circuitry SW 2  in this way once every few seconds or minutes or at other suitable times to check the attachment status of electronic device  10 . 
     At times after time t 0 , electronic device  10  is no longer attached to output line  73 . As a result, when switching circuitry SW 2  is opened at time t 1 , electronic device  10  no longer supplies a load to output line  73 . This allows Vbus to rise to the level of voltage Vaux that is supplied at output OUT of voltage regulator  52 , as indicated by sloping segment  87  of curve  86 . Monitor  54  can monitor this rise in voltage Vbus using path  60 . When a predefined threshold voltage such as threshold voltage Vth 2  is reached at time t 2 , monitor  54  can conclude that electronic device  10  has been removed from power converter  12 . Monitor  54  can therefore issue a power-down command to power converter circuit  122  over control path  76  to place AC-DC power converter circuit  122  and power converter  12  into a standby power consumption mode. In this mode, switching circuit SW 2  remains open, so voltage Vbus may rise to Vaux at times t between times t 2  and t 3 . 
     Line  88  in the graph of  FIG. 4  illustrates how the voltage Vstore on path  66  at the output of capacitor  80  may evolve as a function of time when electronic device  10  is detached from power converter  12 . At time ti, power converter  12  is in standby mode. In standby mode, power converter circuit  122  is off (i.e., not actively switching switch SW 1 ) and monitor  54  is being powered by stored energy in capacitor  80 . Initially, at time ti, capacitor  80  has a voltage Vstore of Vsec (i.e., the nominal output voltage on output  64  that is produced by power converter circuit  122  when power converter circuit  122  is active). 
     During times ti to td, monitor  54  operates to detect changes in the attachment status of electronic device  10 . This consumes power and depletes capacitor  80 , leading to the decrease in voltage Vstore from Vsec to Vth 4 , as indicated by curve segment  90 . 
     At time td, Vstore drops below a predetermined threshold voltage Vth 4 . When monitor  54  detects that Vstore has dropped below Vth 4 , monitor  54  may issue an activation control command on path  76  that turns on power converter circuit  122 . Once power converter circuit  122  is placed in active mode at time td, the output voltage on output  64  will rise to nominal output value Vsec, as indicated by line segment  92  of curve  88 . 
     Monitor  54  can monitor the replenishment process represented by line segment  92  to confirm when Vstore has returned to its fully replenished state or can direct power converter circuit  122  to remain active for a given period of time (e.g., a period such as a few seconds that is sufficient to recharge capacitor  80 ). At time tr, after capacitor  80  has been replenished, monitor  54  can place power converter circuit  122  in standby mode. As indicated by line segment  94 , the depletion process of line segment  90  then repeats. Monitor  54  can turn power converter circuit  122  on and off as shown in  FIG. 4  for as long as required (i.e., until electronic device  10  is attached). 
     The graph of  FIG. 5  illustrates how voltage Vbus may evolve during the process of attaching electronic device  10  to power converter  12 . At time ts, electronic device  10  is not attached to power converter  12 . In the absence of a load on output line  73 , the voltage Vbus rises to Vaux to match the unloaded output voltage of voltage regulator  54 , as shown by line segment  98  of curve  96 . At time ta, a user attaches electronic device  10  to power converter  12  (e.g., by connecting a USB cable or other cable between device  10  and power converter  12 ). Once device  10  is connected to output line  73 , device  10  begins to load output line  73 . 
     Current limiting circuit  52 B prevents voltage regulator  52  from providing the full amount of current that is demanded by electronic device  10 . This causes voltage Vbus to drop from Vaux at time ta to a predetermined threshold voltage such as Vth 3  at time tb, as indicated by line segment  100 . When monitor  54  detects that voltage Vbus has dropped to Vth 3 , monitor  54  can conclude that electronic device  10  has been attached to power converter  12 . Monitor  54  can therefore issue a command to power converter circuit  122  over path  76  that places power converter circuit  122  in its active mode. 
     Once power converter circuit  122  is activated, the output voltage from power converter circuit  122  can supply power to electronic device  10 , allowing voltage Vbus to rise to its nominal value Vsec, as indicated by line segment  102  in  FIG. 5 . At times after time tc (e.g., along line segment  104 ), Vbus may be held at voltage Vsec by converter control circuit  38 . 
       FIG. 6  shows how Vbus may evolve when monitor  54  opens switching circuitry SW 2  while electronic device  10  remains attached. At time tbg, power converter  12  is active and is powering electronic device  10  by supplying a voltage Vbus of Vsec. At time top, monitor  54  opens switching circuitry SW 2 . Because electronic device  10  is connected to power converter  12 , voltage Vbus drops. When a predetermined threshold voltage Vth 1  is reached at time tcl, monitor  54  can conclude that electronic device  10  is still connected to power converter  12  and can close switching circuitry SW 2 . Voltage Vbus preferably remains above voltage Vmin (e.g., about 4.5 volts) to prevent electronic device  10  from erroneously concluding that electronic device  10  has been disconnected from power converter  12 . Once switching circuitry SW 2  is closed, power is restored to output line  73  and voltage Vbus will rise, reaching nominal output voltage level Vsec at time tfn. 
     A diagram showing how power converter  12  and device  10  may operate in system  8  of  FIG. 1  as a user attaches and detaches device  10  from converter  12  is shown in  FIG. 7 . 
     In active mode  106 , power converter  12  is operating normally as an AC-DC power converter and is supplying power to an attached electronic device  10  from AC source  14 . In a typical scenario, electronic device  10  contains a rechargeable battery that can be recharged when electronic device  10  is connected to power converter  12 . During the operations of mode  106 , monitor  54  primarily holds switching circuitry SW 2  closed to allow power to be delivered from line  64  to output line  73  and electronic device  10 . At appropriate times (e.g., once every few seconds, minutes, etc.), monitor  54  momentarily opens switching circuitry SW 2  to check whether electronic device  10  is still attached. If voltage Vbus does not rise when switching circuitry SW 2  is opened (e.g., if voltage Vbus falls to Vth 1  as described in connection with  FIG. 6 ), monitor  54  can conclude that electronic device  10  is still attached to power converter  12 . As indicated by line  108 , the operations of active mode  106  can then continue uninterrupted. 
     If, however, voltage Vbus rises to threshold Vth 2  when switching circuitry SW 2  is opened as described in connection with  FIG. 3 , monitor  54  can conclude that device  10  has been detached. As shown by line  110 , monitor  54  can then place power converter circuit  122  and power converter  12  in standby mode  114 . 
     During standby mode  114 , power converter circuit  122  is not active, so power converter circuit  122  is not able to deliver power for powering monitor  54 . Rather, power is supplied from energy storage circuit  50 . In particular, energy storage circuit  50  may supply a voltage Vstore to monitor  54  and to input IN of boost converter  52 A ( FIG. 2 ). So long as the voltage level of voltage Vstore is sufficient (i.e., above Vth 4 ), energy storage circuit  50  can be used to power monitoring circuit  54  and voltage regulator  52 . During this time, monitor  54  may periodically check the attachment status of electronic device  10 . If voltage Vbus falls below Vth 3  during one of these checks as described in connection with  FIG. 5 , monitor  54  can return power converter circuit  122  and power converter  12  to active mode  106 , as indicated by line  112 . If monitor  54  determines the voltage Vstore falls below Vth 4  as described in connection with  FIG. 4 , monitor  54  can momentarily activate power converter circuit  122  (active mode  118 ). In active mode  118 , power converter circuit  122  is active and replenishes energy storage element  50  (e.g., by recharging capacitor  80  path  66 ). Device  10  remains detached during the operations of mode  118 . 
     After voltage Vstore has been restored (line segment  92  of  FIG. 4 ), monitor  54  may return power converter circuit  122  and power converter  12  to standby mode  144  to conserve power, as indicated by line  120 . 
     If desired, Vaux can be provided at a different level (e.g., a level that is greater than the minimum operating voltage of device  10  or other such load but that is not greater than Vsec). In the example of  FIGS. 4 ,  5 ,  6 , and  7 , the use of a Vaux value that is greater than Vsec helps facilitate the detection of the attachment state of device  10  when opening of switch SW 2 . In scenarios in which Vaux is not greater than Vsec, the presence of device  10  or other such loads may be detected by determining that the voltage Vbus has not fallen (e.g., Vbus has not fallen past a particular threshold voltage). Configurations in which Vaux is greater than Vsec are sometimes described herein as an example. This is, however, merely illustrative. 
     As shown in  FIG. 8 , the circuitry of system  8  may be incorporated into all or part of an electronic device such as device  300 . Device  300  may be a portable computer, a handheld computing device, a desktop computer, consumer electronics equipment such as a television or stereo system, a computer display, a game controller, or any other suitable electronic equipment. During normal operation, device  300  may be powered by the circuitry of power converter  12 . This allows the circuitry of device  300  to be fully powered. Circuit components in device  300  are shown schematically as device circuit  210  in  FIG. 8  and may include electronic components such as user interface components (e.g., touch screens, touch pads, mice, keys, buttons, circuitry for receiving wireless user commands such as infrared receiver circuitry that monitors signals from remote controls, radio-frequency wireless communications circuitry that monitors user signals, processing and storage circuitry, sensors, etc.). 
     Energy storage circuit  50  may be charged during normal operation. When it is desired to conserve power, circuit  122  can be placed in a reduced-power (standby) mode of operation. In standby, device circuit  210  may await activity that indicates that device  300  should resume normal operation. For example, device circuitry  210  may include infrared receiver circuitry or other user input circuitry that monitors user input activity or other suitable events. When a user supplies an infrared command or other activity is detected by device circuit  210 , the resulting behavior of device circuit  210  may cause the voltage on line  72  to change. Monitor  54  can sense this change in voltage and may issue a corresponding wake-up command to converter circuit  122  via path  76 . Monitor  54  can also periodically awaken converter circuit  122  to replenish energy storage circuit  50 , as described in connection with  FIG. 1 . 
     If desired, circuit  210  can inform monitor  54  that user input or other monitored activity has been detected using other types of signaling schemes. Consider, as an example, the arrangement of  FIG. 9 . As shown in  FIG. 9 , electronic device  300  may have a power supply such as an AC-DC power converter circuit  122  that charges energy storage and power (voltage) regulator circuit  302 . Circuit  302  may be, for example, a circuit that includes an energy storage circuit such as energy storage circuit  50  of  FIG. 8  and that optionally includes a voltage regulator or other circuit that helps regulate the output of the energy storage circuit when powering circuit  210 . 
     Processor  304  may include storage and processing circuitry such as one or more microprocessors and other control circuits (e.g., integrated circuits, etc.). Processor  304  may be used in controlling the operation of device  300  and circuit  210 . 
     During normal operation of device  300  of  FIG. 9 , power supply  122  may power circuit  302 , so the energy storage circuit  302  can be charged. Circuit  210  and processor  304  can be powered and can operate normally. When it is desired to conserve power, power supply  122  may be placed in standby (e.g., by processor  304 , monitor  210 , or other control circuitry). In standby, the energy storage circuit can be used to power circuit  210  over path  306  and can be used to power monitor  54  over path  308 . 
     Circuit  210  can await user input such as an infrared remote control command or other suitable event that indicates that device  300  should be taken out of standby mode. When such an event is detected, circuit  210  can inform monitor  54  of the occurrence of the event by sending signals over path  310 . Path  310  can be an analog or digital path having one or more associated lines for conveying communications between circuit  210  and monitor  54 . 
     Once monitor  54  determines that it is appropriate to wake up power supply  122  to handle the user input command or other event, monitor  54  can issue an appropriate wake-up control command for power supply circuit  122  over path  76 . Monitor  54  can also periodically wake up power supply  122  when it is desired to replenish the energy storage circuit in energy storage and power regulator circuit  302  via path  210 . 
       FIG. 10  shows how device  300  may have multiple power supply circuits  122 . In the  FIG. 10  example, device  300  has power supply circuit PS 1  and power supply circuit PS 2 . Power supply PS 1  may be a high-power (primary) power supply that supplies tens or hundreds of watts of power, and power supply PS 2  may be a low-power (secondary) power supply that supplies less power (e.g., ten or fewer watts of power). In standby, each supply may consume only a fraction (e.g., 1-10%) of its active power capacity (as an example). These are merely illustrative examples. Primary supply PS 1  and secondary supply PS 2  may have any suitable power supply capacities if desired. 
     During normal operation, power supply PS 1  may be in its active state and may supply power to circuit  210 , processor  304  and other components in device  300 . To conserve power, power supply PS 1  may be placed in a low-power standby state when full power is not needed. Likewise, power supply PS 2  can be placed in standby to conserve power when active operation is not required. During standby, energy storage and voltage regulator circuit  302  may supply power to circuit  210 , as described in connection with  FIG. 9 . From time to time, the energy storage circuit in circuitry  302  may need to be replenished. As described in connection with the circuit of  FIG. 1 , monitor  54  can monitor the state of the energy storage circuit. When replenishment is desired, monitor  54  can issue a replenishment control signal to power supply PS 2  over path  314 . In response, power supply PS 2  can awaken from its standby state. Because power supply PS 2  uses less energy than power supply PS 1  and because the entire device  300  need not be powered during replenishment operations with power supply PS 2 , the use of power supply PS 2  to replenish the energy storage circuit while power supply PS 1  remains in standby can help conserve power. 
     If circuit  210  detects user input or other activity that indicates that device  300  should enter its active state, circuit  210  can direct monitor  54  to wake up power supply PS 1  via path  316 . Monitor  54  can also awaken power supply PS 2 . If desired, circuit  210  can also use processor  304  to issue wakeup commands and other control commands. Processor  304  may, for example, wake up power supply PS 1  whenever user input is received with circuit  210 , whereas monitor  54  may be used in waking up power supply PS 2  (as an example). 
     An illustrative configuration for power adapter  12  such as power adapter  12  of  FIG. 1  is shown in  FIG. 11 . As shown in  FIG. 11 , the power adapter may have a housing such as housing  318  in which circuitry such as circuitry  12  of  FIG. 1  may be mounted. Conductive prongs  320  may be used to connect the power adapter to AC line power. Cable  322  may be used to route output signals from adapter  12  to connector  324 . Connector  324  may be used to connect the power adapter to electronic device  10 . Connector  324  may be, for example, a 30-pin connector of the type that is sometimes used in coupling music player and telephone devices to computers and power supplies. Connector  324  may, in general, have any suitable number of contacts. The use of a 30-pin arrangement is merely illustrative. 
       FIG. 12  shows another illustrative power adapter arrangement. In the configuration of  FIG. 12 , power adapter circuitry  12  of  FIG. 1  is mounted within housing  326 . Connector  328  in the  FIG. 12  example may be a magnetic connector such as a MagSafe® connector from Apple Inc. of Cupertino, Calif. This type of connector uses magnet attraction to help secure connector  328  to a mating device. There may be, for example, magnets in portions  330  of connector  328 . Plug type connectors may also be used in power adapter  12  if desired. 
     As shown in  FIG. 13 , energy storage circuit  50  may form part of AC-DC power converter circuit  122 . For example, converter circuit  122  may be a converter circuit of the type that has a capacitor across its positive and ground output lines (e.g., for filtering). In this type of arrangement, energy for powering monitor  54  and for powering circuits such as circuit  210  (device  10  in the  FIG. 13  example) may be stored within this filter capacitor, without the need for additional energy storage devices. In general, energy storage circuit  50  may be formed from any number of suitable components (capacitors, batteries, etc.) and these components may form stand-alone circuits or may be combined into other circuits in system  8  if desired. Examples such as the illustrative configuration of  FIGS. 1 and 13  are merely illustrative. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.

Metadata:
Filing Date: 20120319
Publication Date: 20140401
Grant Date: 20140401
Priority Date: 20090212
Inventors: SIMS NICHOLAS A.
TERLIZZI JEFFREY
Assignee: APPLE INC
CPC Classifications: [{"code": "H02M7/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M7/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M7/155", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M1/0032", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M1/4258", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M1/0083", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02B70/10", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 42136124