Patent Publication Number: US-2007105415-A1

Title: Power connector with automatic power control

Description:
FIELD OF THE INVENTION  
      This invention is related generally to connectors for use with electronic devices, and more particularly to a power connector with automatic power control.  
     BACKGROUND OF THE INVENTION  
      Many modern consumer or office electronics use AC-DC power supplies as a power source to operate the electronic device or recharge an internally-contained battery. AC-DC power supplies (which are often referred to as “AC-DC power adapters”) take AC electrical power, for example from a wall outlet, and convert it to DC power for use by the electronic device. Electronic devices sold in the market today have widely diverse requirements for the DC power supplied by the AC-DC power adapter in terms of voltage and current. For example, common voltage ratings for AC-DC power adapters include 5 VDC, 6 VDC, 7.5 VDC, 9 VDC, 12 VDC, 15 VDC, etc. Common current ratings for AC-DC power adapters are 500 mA, 1A, 2A, etc. In addition, polarity requirements for the supplied DC power vary among electronic devices.  
       FIG. 1  is a diagram of a typical AC-DC power adapter arrangement  100  and an electronic device  114 . AC-DC power adapter  100  includes an AC-DC power adapter body  102 , AC electrical plug  104  and power adapter plug  108 . AC-DC power adapter  100  is arranged so that the AC electrical plug  104  takes AC power, for example from a wall outlet (not shown) at 110 VAC, and converts it to DC power in the power adapter body  102  which is then supplied at power adapter plug  108 . The supplied DC power has specifications (i.e., voltage, current and polarity) that are intended by the manufacturer to be appropriate for the power requirements of a specific electronic device. Electronic device  114 , as shown in  FIG. 1 , includes a DC power jack  118  that is arranged to receive power adapter plug  108  to thereby take DC power from the AC-DC power adapter  100  and deliver it to the electronic device  114 .  
      A common problem is that a user may easily, but mistakenly, connect an incompatible AC-DC power adapter to an electronic device. In other words, the user may accidentally plug an AC-DC power adapter into an electronic device for which it is not designed to work, even though the AC-DC power adapter appears outwardly to be the correct one and indeed may have a power adapter plug that may be readily plugged into the electronic device&#39;s DC power jack.  
      Such problems occur for a number of reasons. The power adapter plugs commonly used with AC-DC power adapter often look the same and physically interact in a similar manner with the corresponding DC power jack in the electronic device. For example, the Switchcraft brand 765/712 type two-conductor connector set is widely used in the electronics industry. The cylindrical plug portion of this connector set is configured with an annular conductor arrangement having a hollow center pin and typically has the same outside diameter (OD) with varying internal diameters (ID), for example, 2.1 mm, 2.3 mm or 2.5 mm. The corresponding connector portion of the Switchcraft 765/712 set—often referred to as a “jack” (e.g., the DC power jack  118  shown in  FIG. 1 )—includes a center pin that is arranged to slideably engage with the ID of the cylindrical plug to create a first power conducting path. The OD of the cylindrical plug slideably engages with a plug receiving portion of the DC power jack (often in a friction-fit type arrangement) to create a second power conducting path. The power conducting paths are used for power and ground paths where the particular polarity of the paths is a design choice of the AC-DC power adapter manufacturer.  
      As a result, as in the example above, a power adapter plug can be physically connected to an electrically incompatible product so long as its ID is the same size or larger than the OD of the pin of the DC power jack. However, because the plug and jack are at least mechanically compatible, the user may think that the AC-DC power adapter is, in fact, appropriate for the user&#39;s electronic device. That is, there is no clear feedback to the user that the AC-DC power adapter may be wrong other than the electronic device not operating properly or becoming damaged, or through that familiar electrical burning smell which rather strongly indicates that something really has gone wrong. By the time the user looks to the electrical specifications which are typically printed on a label on the AC-DC power adapter, finds the corresponding power requirements for the electronic device (i.e., nominal voltage, current and input polarity), and then determines that the AC-DC power adapter is the wrong one for the device, it may be too late and serious and irreversible problems with the electronic device or AC-DC power adapter may have already occurred.  
      The consequences of using the wrong AC-DC power adapter (i.e., one that is not designed for the specific electronic device with which the AC-DC power adapter is being used) are significant. A safety issue may be created if the use of a wrong AC-DC power adapter causes the electronic device (or the AC-DC power adapter itself) to generate excessive heat or catch fire; the electronic unit may be damaged and/or become inoperable; or the electronic device may not perform to specification.  
      Many typical electronic devices include certain design measures to address the above-noted safety issue for regulatory and product-liability reasons, among others. Some also employ circuits which provide some degree of electrostatic discharge (ESD) or electrical surge protection. However, while satisfactory in some applications, none of these schemes provide a capability to protect the electronic device from damage when a wrong AC-DC power adapter is plugged in, nor provide the user with straightforward and complete feedback that a chosen AC-DC power adapter is the right one for the electronic device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  is a block diagram of a conventional AC-DC power adapter arrangement as practiced in the prior art;  
       FIG. 2  is a block diagram of a conventional implementation of a power circuit incorporating a DC power jack as practiced in the prior art;  
       FIG. 3  is a block diagram of an illustrative smart power connector with automatic power control; and  
       FIG. 4  is a block diagram of an illustrative smart power connector module.  
    
    
     DETAILED DESCRIPTION  
       FIG. 2  is a block diagram of a conventional implementation of a power circuit  200  incorporating a DC power jack as practiced in the prior art. Jack  201  is arranged to couple an external power supply (such as an AC-DC power adapter not shown in  FIG. 2 ) to a main circuit  295  of a typical electronic device such as a mobile telephone, portable music player, etc. Protection element  202  is arranged in parallel between positive and negative busses  203  and  205 , as shown in  FIG. 2 . Protection element  202  provides ESD, surge, and over-voltage protection and is typically configured as a voltage-clamping device. Conventional power circuits may use one or more protection elements. In this example, a second protection element  210  is arranged in parallel with protection element  202  in power circuit  200 .  
      Fuse  208  is arranged in series along bus  203 . Fuse  208  provides over-current protection and is typically a one-time-fuse or a resettable fuse. In this example, fuse  208  is disposed between the protection elements  202  and  210 .  
      Over-voltage and over-current is provided in the conventional implementation by using such fuse plus voltage clamping schemes shown in  FIG. 2 . When current in bus  203  exceeds a threshold, fuse  208  disconnects, either temporarily or permanently. During an over-voltage condition, excessive current may also pass through fuse  208  causing it to disconnect.  
      Conventional power circuits may prevent the electronic device containing main circuit  295  from becoming a safety hazard by catching on fire, but may not prevent the device from becoming damaged. For example, if a permanent fuse is used in the power circuit  200 , once the fuse is permanently disconnected (i.e., “blown”), the electronic device will no longer function. Or, if the input voltage applied at jack  201  is too high due to the use of an incorrect AC-DC power adapter, the applied voltage may not be high enough to trip the protection elements  202  and/or  210  (which means no safety hazard is present), but the applied voltage may still be high enough to damage the main circuit  295 . Conventional power circuit  200  also does nothing to prevent malfunctioning of the electronic device containing main power circuit  295  when an AC-DC power adapter is utilized that is out-of-specification and provides an under-voltage condition.  
      From the user&#39;s perspective, a conventional power circuit&#39;s indicator provides only limited information. Typically a single light emitting diode (LED) is utilized as a “Power LED” which lights to indicate that power has been applied to an electronic device. However, the Power LED does not indicate to the user whether the correct AC-DC power adapter is being used. In other words, the function of this Power LED is really limited.  
       FIG. 3  is a block diagram of an illustrative “smart” power connector with automatic power control. A smart connector arrangement  300  is used to couple an external power supply (such as an AC-DC power adapter) to an electronic device&#39;s main circuit  395 . The term “smart” is used here to refer to an structural arrangement that has an ability to sense aspects of the environment in which it operates and take action in response to changes in that environment. It is further emphasized that all electronic devices that use external power supplies to provide operating power to the device (or to charge on-board batteries) can utilize, and benefit from, a smart power connector as described herein.  
      Smart connector arrangement  300  is typically packaged separately from main circuit  395  so that existing main circuit designs may readily be upgraded with the additional protection and optional user-feedback features provided by the smart power connector. However, in applications where, for example, a new main circuit is designed, then smart connector  300  is combined with main circuit  395  as indicated by reference numeral  375  in  FIG. 3 . In such an approach, the circuits used to implement smart connector  300  use common packaging (in the case of an implementation using integrated circuits) or a common circuit board (in the case of an implementation using discrete components) with main circuit  395  of the electronic device.  
      DC power jack  301  provides an interface to an AC-DC power adapter such as that indicated by reference numeral  100  in  FIG. 1 . DC power jack  301  is thus arranged to be removably engagable with a power adapter plug of an AC-DC power adapter. That is, power adapter plug  108  as shown in  FIG. 1  and DC power jack  301  are configured as mating connectors and will typically include corresponding mechanical interfaces and electrical interfaces to thereby enable a DC power path to be established through the respective mated connecting elements. It is emphasized that the use of the terms “jack” and “plug” herein is arbitrary and is not intended as a limitation. Any set of mateable connectors may be used to realize the benefits and advantages of a smart power connector and either portion of a mateable connector set may be used for DC power jack  301  and power adapter plug  108 , respectively, according to the requirements of the specific application.  
      The respective mateable connectors described above can take any of a variety of connector configurations including both friction fit (as with the Switchcraft brand 765/712 power plug/jack) or mechanically locking type connectors. For example, in some applications, a positive locking type connector is used where the engagement and/or disengagement of the jack and mateable plug require the actuation of a mechanism by the user such as a catch or latch.  
      Other connector types containing multiple circuit paths (where such circuit paths are typically used for purposes in addition to supplying power to an electronic device) are alternatively utilized. For example, mating connectors used in electronic devices that interact with docking equipment (e.g., docking “cradles”) often use multiple circuits to establish data/communications paths between the electronic device and the docking device. Electronic devices such as personal digital assistants and music players are often used with docking cradles to perform synchronization or other functions with a personal computer or other external apparatus. The electronic devices are typically simultaneously charged or powered through the docking cradle connector.  
      As shown in  FIG. 3 , DC power jack  301  includes two lines  302  and  303 —one line functioning as a power conductor and one functioning as ground. Lines  302  and  303  are coupled to polarity correcting device  305 . This device corrects for polarity of the DC voltage applied to DC power jack  301  when a power adapter plug  108  is coupled to connector  301  to thereby supply power from AC-DC power adapter (e.g.,  100  in  FIG. 1 ). Polarity correcting device  305  may alternatively disconnect power from connector  301  if it is the wrong polarity. Polarity correcting device  305  thus ensures that the polarity of the applied DC power will not cause damage to the main circuit  395  of the electronic device.  
      Polarity correcting device  305  is arranged from a variety of electronic devices, depending on the specific characteristics desired. For example, polarity correcting device  305  is alternatively arranged from conventional elements such as diodes, a bridge rectifier, MOS-FETs (metal-oxide-semiconductor field effect transistors), and the like.  
      Power supply  311  is coupled to connector  301  as shown in  FIG. 3 . Power supply  311  receives power from the external power supply (typically AC-DC power adapter  100  of  FIG. 1 ) via connector  301 . Power supply  311  distributes appropriate power to the various operative elements contained in the smart connector arrangement  300 . Such power distribution is not illustrated in  FIG. 3 .  
      Power supply  311  taps power upstream of polarity correcting device  305  to ensure that power is supplied to the operative elements of arrangement  300 , and in particular the user interface  340  (which is described in detail below) so that such operative elements can work normally even in the case when power is supplied from a reverse polarity AC-DC power adapter and polarity correcting device  305  is arranged to thereby disconnect power from connector  301 . Accordingly, some or all of the operative elements of arrangement  300  may be optionally arranged from polarity-insensitive devices. In particular, it is generally preferable that the user interface  340  be configured so that it is powered even in the case where the input power applied to connector  301  is from a reversed polarity AC-DC power adapter. Being thus powered, user interface  340  is thereby capable of providing an alert to the user to indicate that the AC-DC power adapter is incorrect for the application.  
      Power controller  320  is coupled to polarity correcting device  305  via lines  306  and  307  as shown in  FIG. 3 . In this illustrative example, power controller  320  is arranged to perform a switching function to allow or disallow power to be passed to main circuit  395  in response to a control signal from the voltage sensor  325 . In alternative arrangements, power controller  320  is arranged to perform an over-current protection function or voltage clamping function in a conventional manner.  
      Voltage sensor  325  is coupled to lines  306  and  307  to detect the polarity corrected voltage at the output of polarity correcting device  305 . Voltage sensor  325  compares the detected voltage against a reference which defines operating specifications, for example nominal voltage plus a tolerance, for the main circuit  395 . Such operating specifications are pre-defined for proper function of main circuit  395  by the designer or manufacturer of the main circuit  395  of the electronic device.  
      If the detected voltage exceeds the reference then voltage sensor  325  outputs a control signal to power controller on line  327 . Power controller  320  performs a switching function to turn power off to main circuit  395  in response to the received control signal from voltage sensor  325  on line  327 . Alternatively, power controller  320  is configured to clamp the voltage applied at its inputs to a specified operating level in response to the control signal from voltage sensor  325 .  
      Voltage sensor  325 , in this illustrative example, is implemented using a voltage comparator with associated logic circuits. The pre-defined reference sets a limit for the nominal operating voltage of main circuit  395  plus a tolerance limit. The voltage comparator compares the reference against the output voltage from the polarity correcting device  305  while making any correction necessary to offset the voltage drop across the polarity correction device  305 . The reference is implemented using any of a number of techniques. For example, in this illustrative smart connector the reference is implemented as a voltage reference using a circuit comprising discrete zener and switching diodes (not shown in  FIG. 3 ). However, other arrangements (such as look up table) may be utilized according to the specific requirements of an application.  
      As shown in  FIG. 3 , protection elements  344  and  348  are arranged in a parallel configuration between lines  306  and  307 , and disposed on either side of power controller  320 . Protection elements are optionally used depending on the specific requirements of the application. Protection elements  344  and  348  are configured to provide ESD, surge, and/or over-voltage protection and may comprise voltage-clamping devices.  
      User interface  340  is optionally used in the smart connector arrangement  300 . User interface  340  is coupled to voltage sensor  325  via line  339  and provides easy-to-understand feedback so that the user immediately knows if the AC-DC power adapter plugged into an electrical device employing a smart power connector is compatible with the device or not. User interface  340  may be arranged from visual indicators (e.g. one or more light emitting diodes (LED) using one or more colors for the LED, or other information-communicating devices), audio indicators (e.g., buzzers or other tone generators), or a combination of both visual and audio indicators. In this illustrative example, user interface  340  comprises a set of LEDs in respective green, red and amber colors along with an audible indicator such as a buzzer.  
      The smart connector arrangement shown in  FIG. 3  is preferably configured to be fully automatic in operation. Once a power adapter plug  108  ( FIG. 1 ) from AC-DC power adapter  100  ( FIG. 1 ) is plugged into the DC power jack  301 , the arrangement  300  is configured to operate as described above without any other interaction from a user.  
      The operative elements shown in  FIG. 3 , including the polarity correction device  305 , protection elements  344  and  348 , voltage sensor  325 , power controller  320 , and user interface  340  are implemented using a variety of known ways. For example, the features and functions of a smart power connector may be implemented using discrete devices or integrated circuits (or a combination of both). Similarly, the voltage comparator function of voltage sensor  325  may be implemented using a standard, off-the-shelf voltage comparator, OPAMP (operational amplifier), or a portion, or all of an application specific integrated circuit (ASIC).  
      There are a variety of ways for voltage sensor  325 , power controller  320  and user interface  340  to interoperate. Table 1, below, provides one illustrative example:  
                           TABLE 1                       Input condition,                   as determined by voltage   Power Controller   User Interface,   Electronic Device       sensor   Switch status   Visual Indicator Status   Status                  Input voltage at connector   On   Green LED on   Normal Operation       within specification       Input voltage at connector   Off   Red LED on   Not working       above specification       Input voltage at connector   On   Amber LED on   Electronic device       below specification           may or may not                   work - Amber                   LED is a warning                   to the user                  
 
      Table 2, below, provides another illustrative example of the interworking of operative elements including voltage sensor  325 , power controller  320  and user interface  340  within smart connector  300 .  
                           TABLE 2                       Input condition,                   as determined by voltage   Power Controller   User Interface,   Electronic Device       sensor   Switch status   Visual Indicator Status   Status                  Input voltage at connector   On   Green LED on   Normal Operation       within specification       Input voltage at connector   Off   Red LED on/audible   Not working       above specification       indicator on (e.g. buzzer)       Input voltage at connector   Off   Amber LED flashing   Not working       below specification                  
 
      The examples shown in Tables 1 and 2 illustrate the feedback feature where clear (i.e., unambiguous) indicators are provided to the user as to whether an AC-DC power adapter plugged into an electronic device is within an acceptable performance range.  
      Several significant form factors are alternatively utilized for the smart power connector. For example, a fully integrated connector may be packaged with the operative elements (and optional elements) shown in  FIG. 3  and described in the accompanying text. The term “integrated” as used here means the collection of features including voltage sensing, power control and optional user interface functions combined with a connector (e.g., a DC power jack) to provide electrical and mechanical connection with a mateable connector disposed in the AC-DC power adapter plug, to thereby create the smart connector product. A smart connector manufacturer may choose specific implementations and combinations of features and optional functions depending upon the requirements of the application taking cost and other factors into account.  
      Another form factor for the smart power connector is shown in  FIG. 4 . There, a connector module  400  is formed by the addition of a connector interface  410  that is arranged to interface with DC power connector  301  and a circuit interface  420  that is arranged to interface with main circuit  395 . Connector interface  410  is configured to be coupled to a connector such as a DC power jack. Other elements shown in  FIG. 4  are similar in form and operation to those shown in  FIG. 3  and described in the accompanying text.  
      The connector module is thereby arranged to provide voltage sensing, power control and optional user interface functions in a discrete, standalone device. The connector module may thus be readily incorporated, for example, into electronic devices on an original equipment manufacturer (OEM) basis to thereby facilitate ready modular integration between a DC power jack and the rest of the circuitry of the electronic device at hand. Similarly, the connector module can be sold to connector manufacturers for integration with traditional or standard connector products. The elements shown in  FIG. 4  and described above in the text accompanying  FIG. 3  are used to implement the connector module as shown, or alternatively may be implemented in an ASIC which may be desirable for some applications.