Abstract:
A power converter capable of providing a range of DC voltages to an external device and a method of providing a range of DC power are provided. The power converter comprises a supply circuit for receiving a request for DC power and for providing the requested DC power. The supply circuit comprises a detection circuit for sensing a connection to an external device, a source controller circuit for determining a DC output power required by the external device, and a converter circuit for generating the required DC output power. The external device comprises a device controller circuit for communicating the request for DC power. A first conductor provides a path for the device to communicate the required DC power to the power converter and for the power converter to supply the required DC power. A second conductor provides a common reference for conducting return current to the power converter.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to power converters and, more particularly, to a DC power source that can provide a range of DC voltages with various current limits to a DC-powered electronic device.  
         [0003]     2. Description of the Related Art  
         [0004]     Currently, most digital devices (especially, personal digital appliances) use DC power as their primary power source. Because the supply of DC power is not standardized, as is AC power, these devices tend to require DC power to be supplied at various voltage levels. Thus, a digital device must be shipped with its own power source. Typically, the power source is in the form of a “brick” or “wall wart” style supply that converts standard AC power (120V or 220V) to the specific DC power required by the particular digital device.  
         [0005]     Providing a power supply with each digital device has many disadvantages. (1) Including a DC power supply with each device increases manufacturing costs and, thus, increases the cost to end-users. (2) Extra solid waste is created when a digital device is discarded. Although it may still be functional, the power supply cannot be used with other digital devices since it is specific to the device. (3) Consumers must keep track of which power supply goes with each digital device they own. (4) Dangerous situations may arise when a confused consumer attempts to use the incorrect power supply with the digital device.  
         [0006]     Thus, there is a need for a universal DC power Source along with a digital Device enabled to work with a universal DC power Source to alleviate these problems.  
       SUMMARY OF THE INVENTION  
       [0007]     In one embodiment of the invention, a power converter capable of providing a range of DC power comprises a supply circuit for receiving a request for DC power from at least one external device and for providing the requested DC power to the at least one external device. The power converter further comprises an input circuit for receiving an input voltage and generating a DC input voltage.  
         [0008]     In another embodiment of the invention, a DC-powered device requiring DC power comprises a device controller circuit for communicating a request for DC power. The DC-powered device further comprises first and second conductors for connecting the DC-powered device to the power converter. The first conductor provides a path for the DC-powered device to communicate the required DC output power to the power converter and for the power converter to supply the required DC output power to the DC-powered device. The second conductor provides a common reference for conducting return current to the power converter.  
         [0009]     In another embodiment of the invention, a method for providing a range of DC power comprises receiving a request for DC power from at least one external device and providing the requested DC power to the at least one external device. The method for providing a range of DC power further comprises generating a DC input voltage from a received input voltage, detecting a connection between the at least one external device and a power converter, determining the DC output power required by the at least one external device, generating the required DC output power from the DC input voltage, and supplying the required DC output power to the at least one external device.  
         [0010]     In another embodiment of the invention, a system for providing a range of DC power comprises a means for communicating a request for DC power from at least one external device, and a means for providing the requested DC power to the at least one external device. The system for providing a range of DC power further comprises a means for receiving an input voltage and generating a DC input voltage, a means for detecting a connection to the at least one external device, a means for determining a DC output voltage required by the at least one external device, and a means for generating the required DC output voltage from the generated DC input voltage. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other features and advantages of embodiments of the invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings.  
         [0012]      FIG. 1  shows a universal DC power source connected to a DC-powered device.  
         [0013]      FIG. 2  is a block diagram of a universal DC power source capable of providing a range of DC voltages to a DC-powered device.  
         [0014]      FIGS. 3A -3F  illustrates the operation of a Source Controller of the universal DC power source of  FIG. 2 .  
         [0015]      FIG. 3A  describes the operation of the Source Controller from the Idle state through the Detect state to the Comm1 state.  
         [0016]      FIG. 3B  describes the operation of the Source Controller from the Comm1 state through the PowerOn1 state.  
         [0017]      FIG. 3C  describes the operation of the Source Controller from the Comm2 state through the PowerOn2 state.  
         [0018]      FIG. 3D  describes the operation of the Source Controller in the constant current phase of the ChLilon state.  
         [0019]      FIG. 3E  describes the operation of the Source Controller in the constant voltage and fast charge phases of the ChLilon state.  
         [0020]      FIG. 3F  describes the operation of the Source Controller in the PowerOff state.  
         [0021]      FIG. 4  illustrates one embodiment of a communications packet formed by a Complex Device.  
         [0022]      FIGS. 5A and 5B  are block diagrams of a Simple Device.  
         [0023]      FIGS. 6A and 6B  are block diagrams of a Complex Device.  
         [0024]      FIG. 7  is a schematic of one embodiment of a power supply of the Complex Device in  FIG. 6B .  
         [0025]      FIG. 8  is a block diagram of a universal DC power source capable of providing DC power to multiple Devices.  
         [0026]      FIG. 9  is a block diagram of a universal DC power source coupled to a universal bridge. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0027]     The invention will be described below with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
         [0028]      FIG. 1  is a block diagram of the invention, which comprises a universal DC power source (Source)  100  that can provide a range of DC voltages with various current limits to a DC-powered electronic device (Device)  200 . In one embodiment, the Source  100  can supply DC voltages from 1.5 VDC to 27 VDC with a current of from 100 mA to 25.5A. The Device  200  has the ability to communicate its voltage and current requirements to the Source  100 . When the Device  200  is initially connected to the Source  100 , the Source  100  detects the presence of the Device  200 . The Device  200  senses the presence of the Source  100  and communicates it power requirements to the Source  100  (e.g., 12 Volts at 600 mA). The Source  100  then provides the required DC power to the Device  200 .  
         [0029]     Referring to  FIGS. 1 and 2 , the Source  100  and the Device  200  are connected to each other through two conductors: Vdc  102  and Vcom  104 . Vdc  102  is used by the Device  200  to communicate its power requirements to the Source  100 . Vdc  102  is also used by the Source  100  to supply the requested power to the Device  200 . Vcom  104  is a common reference or “ground” and is used to conduct return current back to the Source  100 .  
         [0030]     The Device  200  can use two methods or protocols to communicate its power requirements back to the Source  100 , a Simple protocol or a Complex protocol. Although it may be less expensive to implement the Simple protocol, using the Complex protocol increases the accuracy and feature set of the Source  100 .  
         [0031]     Universal Source  100   FIG. 2  shows one embodiment of the Source  100  which comprises a standard AC-DC power converter  110  to generate 32 VDC. In alternate embodiments, as in automotive applications, a step-up DC-DC converter that converts standard 12 V power from a car&#39;s battery to 32V may replace the AC-DC power converter  110 . Similar substitutions may also be made for other applications, such as in commercial aircraft applications.  
         [0032]     A digital Source Controller  150  indicates the Device&#39;s requested voltage through the 8-bit digVdcTarget signal  152 . A variable, step-down DC-DC converter  120  uses the 32 VDC to generate the voltage level requested by the Device  200 . The DC-DC converter  120  may use standard methods such as, for example, linear regulation, switching regulation, etc. The DC-DC converter  120  uses analog signal anaVdcTarget  132 , generated by a digital-to-analog converter  130 , as a reference in the generation of the requested voltage level. In one embodiment, the DC-DC converter  120  must be capable of supplying at least 500 mA of current, should be able to supply  10 A, and can supply requests of up to 25.5 A. In one embodiment, the DC-DC converter  120  is also configurable as a constant current source with the current set by the anaVdcTarget signal  132 . The In V digital signal  154  indicates to the DC-DC converter  120  whether it is configured as a current source or a voltage source. When charging Lithium-Ion batteries, the DC-DC converter  120  is used in the current source mode.  
         [0033]     The DC-DC converter  120  generates the pre Vdc supply  122 , which can be connected to Vdc  102  through a digitally controlled Switch  160 , such as a relay or a P-Channel MOSFET. The Source Controller  150  generates powerOn  155  to signal the Switch  160  when to allow power from the pre Vdc supply  122  to pass through to Vdc  102 .  
         [0034]     The power supplied to Vdc  102  by the DC-DC converter  120  also passes through Rsense  162 . The resistance of Rsense  162 , chosen to be small, is used to determine the amount of current that the DC-DC converter  120  is supplying to the Device  200 . A differential amplifier  164  detects the small voltage generated by Rsense  162  and converts the differential voltage into a common-mode anaidc signal  172  referenced to Vcom  104  representing the current flowing from the DC-DC converter  120  into Vdc  102 . An analog-to-digital converter  174  converts anaidc  172  into a  12 -bit digidc signal  176 , which is fed into the digital Source Controller  150 .  
         [0035]     The diode  164  between Rsense  162  and Vdc  102  prevents current from flowing backwards from Vdc  102  into pre Vdc  122  during communication. In other words, during communication, the total capacitance of Vdc  102  on the Source side must look small. However, the DC-DC converter  120  must have large capacitors associated with it for stability. Thus, during communication, the combination of the Switch  160  and the diode  164  isolates the large capacitance of the DC-DC converter  120  from Vdc  102 .  
         [0036]     An 8-bit analog-to-digital converter  180  samples the voltage level of Vdc  102  and converts it to an 8-bit digital digVdc signal  182 . The digital Source Controller  150  uses digVdc  182  during communication with the Device  200  and also for monitoring the voltage level produced by the DC-DC converter  120 . A comparator  184  compares the voltage level of Vdc  102  against a known reference  186  (in one embodiment, the reference is 1.0V) to generate the logvdc signal  188 . The logVdc signal  188  is also used during communication with the Device  200 .  
         [0037]     The Source  100  further comprises a 5 mA current source  190 , referred to as the Low Beacon, and a 50 mA current source  192 , referred to as the High Beacon. The Low Beacon  190  and High Beacon  192  current sources, controlled (i.e., turned off or on) by the digital Source Controller  150 , sense the presence of a Device  200  and power the Device Controller ( 500  in  FIGS. 5A and 5B  or  600  in  FIGS. 6A and 6B ) during communication. In the embodiment shown in  FIG. 2 , the Low Beacon  190  and High Beacon  192  current sources are powered by the 32 VDC supply  140  and, therefore, can only drive their respective currents onto Vdc  102  if Vdc  102  is less than 29 volts. If Vdc  102  is higher than 29 volts, the Low Beacon  190  and High Beacon  192  current sources will begin to supply less current.  
         [0038]     The shortvdc signal  156  comes from the digital Source Controller  150  and drives the gate of an N-Channel MOSFET device  157 . The circuit comprising the MOSFET  157  and resistor  158  allows the Source Controller  150  to “zero” out Vdc  102  by sinking current from Vdc  102  to Vcom  104 . However, because of the resistor  158  (in one embodiment, about 40 ohms) on the emitter of the MOSFET  157 , the actual amount of current this circuit can sink is limited. It is useful to “zero” out Vdc  102  while only the 5 mA Low Beacon  190  or 50 mA High Beacon  192  current sources are in operation.  
         [0039]     The Source  100  may further comprise LEDs  194 ,  196  to indicate the status of the Source  100  to the user. In one embodiment, a green LED  194  may be turned on by the Source Controller  150  to indicate the Source  100  is successfully supplying power to the Device  200 . In one embodiment, a red LED  196  may be turned on by the Source Controller  150  to indicate that an error has occurred and that the Device  200  is not being powered by the Source  100 .  
         [0000]     Source Controller  150   
         [0040]     The block diagrams in  FIGS. 3A-3F  show the states the digital Source Controller  150  ( FIG. 2 ) progresses through during the operation of the Universal DC Source  100 . The Idle state  310  is the initial state of the Source Controller  150 . When the Source Controller  150  senses that a Device has connected to the Source, the Source Controller  150  moves to the Detect state  320 . At the Com1 state  330 , the Source Controller  150  determines whether the Device connected is a Simple or Complex Device. If the Device is a Simple Device, the Source Controller  150  enters the PowerOn1 state  340  after the Simple Device communicates its power request to the Source. If the Device is a Complex Device, the Source Controller  150  enters the Com2 state  350  to communicate with the Complex Device and enters the PowerOn2 state  360  after the Complex Device communicates its power request to the Source. In the ChLilon state  370 , the Source Controller  150  executes a recharge operation for a Lithium-Ion battery. When the Device is disconnected from the Source, the Source Controller  150  moves to the PowerOff state  399 .  
         [0041]     Refer now to  FIGS. 1, 2 , and  3 A- 3 E for a more detailed description of the operation of the Source Controller  150 . The Source Controller  150  enters the Idle state  310  when the Source  100  is first powered on. While in Idle state  310 , the Source  100  disconnects the DC-DC converter  120  from Vdc  102 , asserts shortvdc  156 , and monitors Vdc  102 . When Vdc  102  approaches 0V, the Source  100  de-asserts shortVdc  156  and asserts loBeaconEn  191 , thus enabling the 5 mA current source  190  in block  312 . The Source Controller  150  then begins to sample Vdc  102 , in one embodiment, with an interval of about 100 us, to determine whether a Device  200  has connected to the Source  100 . If Vdc  102  is less than 28V, the Source Controller  150  determines that a Device  200  has connected to the Source  100  and moves to the Detect state  320 . If Vdc  102  is higher than 28V, the Source Controller  150  determines that no Device is connected to the Source  100  and remains in the Idle state  310  with the loBeaconEn  191  enabled, monitoring for a Device to connect. When a Device  200  connects to the Source  100 , the voltage on Vdc  102  drops due to the relatively high capacitance of the Device  200  compared to the Source  100 . The Source Controller  150  then senses that a Device  200  has connected and moves to the Detect state  320 .  
         [0042]     In the Detect state  320 , the Source Controller  150  de-asserts loBeaconEn  191  and asserts shortVdc  156  until Vdc  102  approaches 0V again. In block  322 , the Source Controller  150  then re-asserts loBeaconEn  191 , de-asserts shortvdc  156 , and monitors Vdc  102  to determine whether the connection between the Source  100  and the Device  200  is reliable. In one embodiment, the Source Controller  150  monitors Vdc  102  for 0.5 seconds, sampling Vdc  102  every 10 ms. If at any time Vdc  102  is sampled above 28V, the connection is deemed unreliable and the Source Controller  150  returns to the Idle state  310 . If the connection is found to be reliable, Vdc  102  is again “zeroed” out by de-asserting loBeaconEn  191  and asserting shortVdc  156  in block  324 . The Source Controller  150  then proceeds to the Com1 state  330 .  
         [0043]     The Com1 state  330  has two purposes. First, at the Com1 state  330 , the Source  100  measures the capacitive load of the Device  200  and determines if it is a Simple or Complex Device. Second, if the Device  200  is a Simple Device, the Source  100  measures the voltage requested by the Device  200  at the Com1 state.  
         [0044]     In the Com1 state  330 , the Source Controller  150  de-asserts shortVdc  156  and then asserts loBeaconEn  191 , thus enabling the 5 mA current source  190  in block  332 . Since the Device  200  should be presenting a predominantly capacitive load and the Source  100  is supplying a constant current into the Device  200 , Vdc  102  begins to ramp in a linear fashion. The Source  100  monitors Vdc  102  and measures the amount of time Vdc  102  requires to attain 1.5V (Tdc). The capacitance of the Device  200  can therefore be calculated by the equation:  
       C   =           I     d   ⁢           ⁢   c       ⁢     T     d   ⁢           ⁢   c           V     d   ⁢           ⁢   c         ≈     .0033   ⁢           ⁢     T     d   ⁢           ⁢   c               
 
         [0045]     Thus, in block  334 , if the capacitance of the Device  200  is measured to be below 0.1 μF, the Device  200  is deemed to be a Complex Device and the Source Controller  150  proceeds to the Com2 state  350 . If the capacitance of the Device  200  is greater than or equal to 0.1 μF, the Device is deemed to be a Simple Device and the Source Controller  150  continues in the Com1 state  330 .  
         [0046]     If the Device  200  is a Simple Device, the capacitance measurement is also used, in block  336 , to determine the maximum amount of average current the Device  200  is requesting. In one embodiment, the parameter values are as shown in Table 1. If the capacitance value is measured at more than 12.5 μF, an error has occurred and the Source Controller  150  goes into the PowerOff state  399 .  
                                                           TABLE 1                                   Measured Capacitance   Maximum Average Current           (Cdc)   (Idc_max)                                        0.1 μF ≦ Cdc &lt; 0.5 μF   500   mA           0.5 μF ≦ Cdc &lt; 2.5 μF   2   A           2.5 μF ≦ Cdc &lt; 12.5 μF   10   A                12.5 μF ≦ Cdc   Reserved               (Error)                      
 
         [0047]     While in the Com1 state  330 , the Source Controller  150 , in block  338 , determines the voltage level requested by a Simple Device. The Source Controller  150  repeatedly samples Vdc  102 . When the Source Controller senses that Vdc  102  has reached a steady value and is no longer ramping, the Source Controller  150  determines that the steady value of Vdc  102  is the voltage level the Device is requesting. The Source Controller  150  then moves to the PowerOn1 state  330 .  
         [0048]     In the PowerOn1 state  330 , the Source Controller  150 , in block  342 , evaluates its ability to meet the Simple Device&#39;s request. Primarily, this involves comparing the requested average current requirements with the Source&#39;s ability to provide this current. If the Source  100  is unable to supply the requested current, the Source Controller  150  moves to the PowerOff state  399 .  
         [0049]     If the Source  100  can supply the requested power, the Source Controller  150  drives digVdcTarget  152  to the DC-DC converter  120  as a reference for the requested voltage level. The Source Controller  150  then turns the Switch  160  on and disables the 5 mA Low Beacon current source  190 , thus supplying power to the Simple Device at its requested levels in block  344 . The Source Controller  150  then, in block  345 , may turn on the green LED  194  to provide status to a user.  
         [0050]     In the PowerOn1 state  330 , the Source Controller  150 , in block  346 , monitors the current sinked by the Simple Device. In one embodiment, if the average current over a 10-second window exceeds the current communicated by the Simple Device during the Com1 state  330 , the Source Controller  150  determines that an error has occurred and the Source Controller  150  moves to the PowerOff state  399 . If the Source Controller  150  monitors the Simple Device&#39;s current at greater than two (2) times the value communicated during the Com1 state  330 , the Source Controller  150  determines that a peak current error has occurred and the Source Controller  150  moves to the PowerOff state  399 . Finally, if the average monitored current over a 10-second window drops below 10 mA (referred to as the Hold current), the Source Controller  150  determines that the Simple Device is disconnected and the Source Controller  150  moves to the PowerOff state  399 .  
         [0051]     If, in the Com1 state  330 , the Source Controller  150  determines that the Device  200  is a Complex Device, the Source Controller  150  enters the Com2 state  350 . In one embodiment, a Complex Device first signals its presence to the Source  100  by pulling Vdc  102  to a voltage level below 1V for a period of at least 50 μs but no more than 500 μs. In the Com2 state  350 , the Source Controller  150 , in block  352 , disables the 5 mA Low Beacon  190  current source and, in block  354 , enables the 50 mA High Beacon  192  current source by asserting hiBeaconEn  193 . The higher level of beacon current is supplied to power the Complex Device&#39;s more complex electronics.  
         [0052]     Next, in block  356 , the Complex Device communicates its requirements to the Source  100 . The Device  200  repeatedly applies and removes a low resistance to Vdc  102 . In one embodiment, the resistance must be low enough such that the voltage level on Vdc  102  drops to less than 1.0V with the 50 mA current source  192  applied. When the resistance is applied and Vdc  102  drops below 1.0V, the Source  100  sees this as the communication of a logical “1”. When the Complex Device is not applying this low resistance, the Source sees this as the communication of a logical “0”.  
         [0053]     A communications packet  400 , shown in  FIG. 4 , is formed by the Complex Device repeatedly signaling a series of logical Is and Os to the Source  100 . In one embodiment, the communications packet  400  formed by the Device comprises a preamble  410  of 0×AA. The preamble  410  sends a representative signal of the Device&#39;s clock to the Source  100 , which synchronizes the Source  100  to the Device. The preamble  410  is used by the Source  100  to measure the unit interval time (UI) of each bit. The time of the UI is nominally 4 μs.  
         [0054]     After the preamble  410  is sent, the Complex Device sends an 8-bit address  420 , an 8-bit data word  430 , and a 5-bit CRC  440 . The address  420  designates to the Source  100  which power supply parameter the respective data word sets  430 . Table 2 shows all legal parameters and the addresses that access them.  
                       TABLE 2                       Address   Parameter   Description                   0x00   Supply   This parameter indicates to the Source           Voltage   what DC voltage the Device is requesting.               This value is in 0.1 V increments (e.g., a               value of 50 (0x32) indicates 5.0 V). This               parameter defaults to 0.       0x01   Average   This parameter indicates to the Source the           Current   maximum average current the Device will               draw. The average is calculated over 10               seconds. If the Device ever exceeds this               value, the Source should shut power off to               the Device. This value is in 100 mA               increments (e.g. a value of 25 (0x19)               indicates 2.5 A). This parameter defaults               to 5.       0x02   Peak   This parameter indicates to the Source the           Current   maximum peak current the Device will               draw. If the source ever samples the               Device&#39;s current at above this value, the               Source should shut power off to the               Device. This value is in 100 mA               increments (e.g. a value of 100 (0x64)               indicates 10.0 A). This parameter defaults               to 10.       0x03   Slew Rate   This parameter indicates to the Source               how fast power should be ramped. This               value is in 0.1 V/ms (e.g. a value of 45               (0x2D) indicates that the supply voltage               will be ramped at the rate of 4.5 V/ms).               This parameter defaults to 10.       0x04-0x0f   Reserved   These addresses are reserved for future               parameters. Writing to them is an error.       0x10   Battery   A non-zero value in this parameter           Charge   indicates to the Source that it is charging a           Current   Lithium-Ion Battery. The parameter               controls the amount of regulated constant               current to be supplied in 50 mA increments               during the constant current phase of               battery charging. This parameter defaults to 0.       0x11   Battery Fast   A non-zero value in this parameter           Charge Time   indicates to the Source that it should use               the fast charge algorithm instead of the               constant voltage phase after the constant               current phase has ended. This parameter               controls the amount of time the constant               current source will be enabled (in 50 ms               increments). This parameter defaults to 0.       0x12-0xfe   Reserved   These addresses are reserved for future               parameters. Writing to them is an error.       0xff   Enable   When this parameter is written with the               value of 0x90 (“GO” command), the               Source applies power to the Device using               the previously communicated parameters               (or their defaults). Any other value than               0x90 written to this parameter is               considered an error. This parameter must               be that last one written by the Device.                  
 
         [0055]     As the Source  100  receives each data bit of the packet  400  (excluding the preamble  410 , but including the CRC  440 ), the Source  100  applies this bit to a Linear Feedback Shift Register (LSFR) with the polynomial X 5 +X 4 +X 2 +1. The polynomial identifies all odd number of bit errors (parity) along with over 99% of two bit errors.  
         [0056]     If after applying all bits of the packet  400  to the LSFR, the remainder in the LSFR is non-zero, the Source Controller  150  determines that a bit error must have occurred. In this case, the Source Controller  150  exits the Com2 state  350  and proceeds to the PowerOff state  399 .  
         [0057]     After the Complex Device communicates a “GO” command (0×90) to the Enable parameter, the Source Controller  150  proceeds to the PowerOn2 state  360 , unless a battery charge operation is requested (indicated by a non-zero value in the Battery Charge Current parameter), the Source Controller  150  proceeds to the ChLilon state  370 . Any other value assigned to the Enable parameter is an error, which causes the Source Controller  150  to move to the PowerOff state  399 .  
         [0058]     In the PowerOn2 state  360 , the Source Controller  150 , in block  362 , evaluates its ability to meet the Complex Device&#39;s request. Primarily, this involves comparing the requested average and peak current requirements with the Source&#39;s ability to provide this current. If the Source  100  is unable to supply the requested current, the Source Controller  150  moves to the PowerOff state  399 .  
         [0059]     If the Source  100  can supply the requested power, the Source Controller  150  drives digVdcTarget  152  to the DC-DC converter  120  with a reference value of 0. The Source Controller  150  then turns the Switch  160  on and disables the 50 mA High Beacon current source  192 . The Source Controller  150  begins to increase the reference value on digVdcTarget  152  at the rate specified by the Slew Rate parameter until Vdc  102  is being driven at its requested voltage level in block  364 . The Source Controller  150  then, in block  365 , may turn on the green LED  194  to indicate status to a user.  
         [0060]     In the PowerOn2 state  360 , the Source Controller  150 , in block  366 , monitors the current sinked by the Complex Device. If the Source Controller  150  measures average current over a 10-second window that exceeds the value of the Average Current parameter, the Source Controller  150  moves to the PowerOff state  399 . Likewise, if the Source Controller  150  measures an instantaneous current that exceeds the Peak Current parameter, the Source Controller  150  moves to the PowerOff state  399 . If the average monitored current (over a 10-second window) drops below 10 mA (referred to as the Hold current), the Source Controller  150  determines that the Complex Device is inactive or disconnected and the Source Controller  150  moves to the PowerOff state  399 .  
         [0061]     If a Device requests a battery charge operation (indicated by a non-zero value in the Battery Charge Current parameter), the Source Controller  150  moves to the ChLilon state  370  and executes a recharge operation for a Lithium-Ion battery. The Source Controller  150  first evaluates its ability to meet the Device&#39;s request in block  371 . Primarily, this involves comparing the requested charging current with the Source&#39;s ability to provide this current. If the Source  100  is unable to supply the requested charge current, the Source Controller  150  moves to the PowerOff state  399 .  
         [0062]     The recharge operation begins with a constant current phase where the Source Controller  150 , in block  373 , configures the DC-DC converter  120  into a current source by asserting the InV signal  154 . The Source Controller  150  then drives digVdcTarget  152  with a reference value corresponding to the amount of current the DC-DC converter  150  should drive. This value is determined by the value programmed into the Battery Current parameter. In block  374 , the Source Controller  150  turns the Switch  160  on allowing the charging current to flow out of Vdc  102  and disables the 50 mA High Beacon current source  192 , thus charging the Device&#39;s battery. The Source Controller  150  then, in block  375 , may turn on the green LED  194  to indicate status to a user.  
         [0063]     In block  376 , the Source Controller  150  monitors the voltage level of Vdc  102 . When Vdc  102  reaches the value programmed into the Supply Voltage parameter (address 0×00), the Source Controller  150  ends the constant current phase of the recharge operation and enters either the constant voltage phase  380  or the fast charge phase  390 . The Source Controller  150  enters the constant voltage phase  380  if the Battery Fast Charge Time parameter is set to 0. The Source Controller  150  enters the fast charge phase  390  if the Battery Fast Charge Time parameter is set to a non-zero value.  
         [0064]     During the constant voltage phase  380 , the Source Controller  150 , in block  381  reconfigures the DC-DC converter  120  to a constant voltage source by de-asserting the InV signal  154  and driving the digVdcTarget  152  with the value of the Supply Voltage parameter. This causes the DC-DC converter  120  to drive the voltage programmed into the Supply Voltage parameter in block  382 . The Source Controller  150  then monitors the current in block  383 . This continues until the battery is fully charged at which time the Device is disconnected in block  384 . The Controller detects this and moves to the PowerOff state  399 .  
         [0065]     During the fast charge phase  390 , in block  391 , the constant current programmed into the Battery Current parameter is applied to Vdc  102  for a period of time determined by the Battery Fast Charge Time parameter. After this time, in block  392 , the Source Controller  150  turns off the current source by turning off the Switch  160 , and the Source Controller  150  monitors the voltage level of Vdc  102  in block  393 . When the voltage level on Vdc  102  drops below the voltage programmed into the Supply Voltage parameter, the Source Controller  150  again applies the current specified by the Battery Current parameter for a period of time specified by the Battery Fast Charge Time parameter. The Source Controller  150  repeats this until a disconnect is detected. In this case, the disconnect is detected when no current flows during the Battery Fast Charge Time period. When the Device is disconnected in block  394 , the Source Controller  150  moves to the PowerOff state  399 .  
         [0066]     In the PowerOff state  399 , the Source Controller  150  disables the Switch  160  and sets the reference digVdcTarget  152  back to 0. The Source Controller  150  then discharges Vdc  102  by asserting shortVdc  156  and may turn on the red LED  196  to indicate status to a user. In one embodiment, the Source Controller  150  waits in this state for at least  10  seconds, after which time the Device should be completely powered off. The Source Controller  150  then proceeds to the Idle state  310 .  
         [0000]     Universal Device  
         [0067]     A Device  200  may use either a “Simple” or “Complex” protocol to communicate its power requirements back to the Source  100 .  FIGS. 5A and 5B  illustrate an embodiment of a Simple Device  200 S that uses the Simple communication protocol.  
         [0000]     Simple Device  
         [0068]     Referring now to  FIGS. 2, 5A , and  5 B, the Zener voltage of Zener diode Dref determines the voltage level requested by the Device  200 S in the Simple Device configuration. The capacitance of capacitor Cref determines the maximum average current requested by the Device  200 S (see Table 1).  
         [0069]     When a Simple Device  200 S is first connected to the Source  100  (or when the Source  100  is first powered on, if it is already connected to the Device  200 S), the Source  100  provides a regulated Low Beacon current of 5 mA. The fixed Low Beacon current charges capacitor Cref such that the voltage of Vdc  102  ramps linearly. The Source  100  then measures this voltage ramp to determine the value of Cref and, therefore, the maximum average current requested.  
         [0070]     The voltage of Vdc  102  continues to ramp under the presence of the Low Beacon current until this voltage reaches the Zener voltage of Dref. At this point, Dref breaks down and begins to sink the Low Beacon current, stopping the voltage ramp of Vdc  102 . After this point, Vdc  102  begins to maintain a constant voltage regulated by Dref. When the Source  100  detects that the ramp has stopped, the Source  100  samples the level of Vdc  102 . The Source  100  then uses this sampled level of Vdc  102  as the voltage level the Simple Device  200 S is requesting.  
         [0071]     In an alternate embodiment, a resistor Rref (not shown) may be used in place of Dref V ref and Q1. Resistor Rref is assigned a value according to the equation  
           R   ref     =       V   ref     0.005       ,       
 
 where Vref is the requested voltage. Essentially, resistor Rref communicates the requested voltage back to the Source  100  according to the voltage it produced by the Low Beacon current (5 mA) passed through it. 
 
         [0072]     A disadvantage with the alternate embodiment is that resistor Rref would not produce the linear ramp that Zener diode Dref produces, thus making it more difficult for the Source  100  to measure the value of Cref, especially for lower values of Vref. Also, it would always draw 5 mA when the Source  100  was supplying proper power and more if the Source  100  supplied a higher voltage than it should be. This may preclude the ability of the Device  200 S to signal a Disconnect. The alternate embodiment using the resistor Rref has the advantage of being simpler and more reliable (from a component failure standpoint).  
         [0073]     The Source  100  then applies power at the requested level. The Voltage Supervisor  560  detects that the Source  100  is providing the requested voltage and, after a predetermined amount of time, asserts powerEnable  562  and de-asserts nRefEnable  561 . When powerEnable  562  asserts, the electronically controlled Switch  570  turns on and gates the power from Vdc  102  onto the Device&#39;s electronic, thus powering the Device  200 S. PowerEnable  562  also causes resistor Rhold to be connected to Vdc  102 . Resistor Rhold maintains at least a 10 mA current load on Vdc  102 . If the Source  100  detects that the Simple Device  200 S is drawing less than 10 mA, it deems that the Device  200 S has disconnected. The de-assertion of nRefEnable  561  causes Dref to be disconnected from Vdc  102 , thus protecting Dref.  
         [0074]     If the Voltage Supervisor  560  detects that the Source  100  is supplying a voltage greater or less than it expects, it de-asserts powerEnable  562  and leaves nRefEnable  561  de-asserted. This effectively turns off the Simple Device  200 S and causes the Source  100  to go to PowerOff.  
         [0000]     Complex Device  
         [0075]      FIG. 6  illustrates an embodiment of a Device  200 C that implements the Complex communication protocol.  
         [0076]     In one embodiment, the Complex Device  200 C must present less than a 0.1 μF capacitive load on Vdc  102  when the electronic controlled Switch  670  is off (i.e., the capacitive loading from the Device&#39;s electronics are isolated from Vdc  102 ). Since there is no Cref present in the Complex Device Controller  600  as with the Simple Device Controller  500  (in  FIGS. 5A and 5B ), all capacitive loading on Vdc  102  is due to the parasitic loads of the components connected to it. In practice, limiting these parasitic loads to below 0.01 μF is easily achieved.  
         [0077]     When a Device presents a small capacitive loading (less than a 0.1 μF capacitive load) on Vdc  102 , the Source  100  detects it as a Complex Device  200 C and supplies the regulated 50 mA High Beacon current. Power from the High Beacon current is used by the Power Supply  630  to generate power for the Complex Device&#39;s digital Controller  660 .  
         [0078]     After the Device Controller  660  powers up, it signals its presence to the Source  100  by asserting commEnable  661 , in one embodiment, for a period of time of no less than 50 is and no more than 500 μs. This causes Q 1  to conduct the entire High Beacon current through Rcomm to Vcom  104  and effectively pulls Vdc  102  to under IV. The value of Rcomm is selected so that it can conduct all 50 mA of the High Beacon without generating a large voltage; in one embodiment, a value of about 10 ohms is reasonable.  
         [0079]     While the Device Controller  660  is signaling its presence to the Source  100 , it samples Vdc  102  with the 8-bit ADC  680  to make certain that it is able to pull Vdc  102  below IV. If it is not, it could mean that the Source  100  has somehow mistakenly started supplying power to the Device  200 C. In this case, the Device  200 C discontinues operation and shuts down. If the Source  100  is mistakenly in a PowerOn state, the Source  100  sees the Device  200 C shutting down as a Disconnect and the Source  100  proceeds to the PowerOff and Idle states and eventually start communications over.  
         [0080]     After successfully signaling its presence to the Source  100 , the Device  200 C begins to communicate its power requirements to the Source  100  using the packet protocol previously discussed for the Com2 state. The logical 1s and 0s are generated by the Device Controller  660  asserting (for a 1) and de-asserting (for a 0) the commEnable signal  661 . After communicating the power requirements, the Device Controller  660  sets the Enable parameter to 0×90 (“GO”), which signals the Source  100  to begin supplying power to the Device  200 C as specified. Any parameters that have not been explicitly set by the Device Controller  660  are set to their default values.  
         [0081]     After communicating a “GO” to the Source  100 , the Device Controller  660  asserts the powerEnable signal  662 , thus turning on the Switch  670  and allowing the power supplied by the Source  100  to reach the Device&#39;s electronics. The Device Controller  660  also asserts the holdEnable signal  663  to connect resistor Rhold to Vdc  102 . In one embodiment, resistor Rhold draws at least 10 mA of current in order to maintain a connection with the Source  100 .  
         [0082]     The Device Controller  660  now begins to sample Vdc  102  with its 8-bit ADC  680 . If the Source  100  does not supply the proper voltage to the Device  200 C requested during communication, (e.g., Vdc  102  is 20V when 12V was requested), the Device Controller  660  de-asserts the powerEnable signal  662  and the holdEnable signal  663  and shuts down. The Source  100  should see this as a Disconnect and start over.  
         [0000]     Power Supply  630   
         [0083]      FIG. 7  shows a schematic diagram of a Power Supply  630  that is able to meet the requirements of a Complex Device  200 C, the requirements including: (1) limit capacitive loading of Vdc  102  during Com1 phase; (2) don&#39;t turn on until Com2 phase; and (3) continue supplying the Device Controller  660  with power even while the Device Controller  660  is pulling Vdc  102  to 0 V by asserting the commEnable signal  661 .  
         [0084]     In one embodiment, the Power Supply  630  comprises a voltage regulator U 4 , a linear 3.3V regulator (for a digital Device Controller  660  requiring 3.3V). The regulator U 4  converts the voltage accumulated on capacitor C 4  into 3.3V as long as the voltage on capacitor C 4  is above about 4V. Capacitor C 4  is charged by the High Beacon current through resistor R 27 , transistor Q 6 , and diode D 9 . Transistor Q 6  acts as a switch that isolates capacitor C 4  from Vdc  102  when it is off. Diode D 9 ,insures that current cannot backflow from capacitor C 4  to Vdc  102  when Vdc  102  is being pulled low by the Device Controller  660  asserting the commEnable signal  661 . Resistor R 27  is an emitter feedback resistor that limits the in-rush current into capacitor C 4  when Q 6  turns on. The output of U 4  is stabilized by capacitor C 5 . Capacitor C 5  also stores energy for use when commEnable  661  is asserted and Vdc  102  is pulled to below 1V. Capacitor C 5  and diode D 9  ensure that the Device Controller  660  does not reset itself whenever it asserts commEnable  661 .  
         [0085]     The power supply  630  comprises U 2 , a reset supervisor and used to time the turn on of transistor Q 6  and, subsequently, voltage regulator U 4 . When the Source  100  enables the Low Beacon current during the Com1 phase and then the High Beacon current during the Com2 phase, C 8  is slowly charged. In the embodiment shown in  FIG. 7 , the power supply  630  further comprises resistor R 3 , which functions to isolate the capacitance of C 8  from Vdc  102 . Although the capacitance of C 8  is less than 0.1 μf, it doesn&#39;t hurt to minimize the capacitive loading on Vdc  102  during Com1. Diode D 10  ensures that capacitor C 8  is not discharged whenever the Device Controller  660  asserts the commEnable signal  661 , which may inadvertently cause the reset supervisor U 2  to reenter its reset cycle. In one embodiment, D 7  is a 5.1 V Zener diode, which functions to ensure that the maximum input voltage of the reset supervisor U 2  is not exceeded.  
         [0000]     Additional Architectures  
         [0086]      FIG. 1  shows a Source  100  supplying only a single Device  200 . However, as shown in  FIG. 8 , nothing in the invention precludes a Universal Source  100  that supplies multiple Devices  200 ( 1 )- 200 ( n ). In this embodiment, a single AC-DC Power Supply  110  and digital Source Controller  150  are used to control all power ports of the Source  100 . However, all other components of  FIG. 8  would be replicated for each port. Moreover the digital Source Controller  150  (although common) would need to be expanded to include the ability to control multiple ports.  
         [0087]     The Source Controller  150  would also be required to budget the power supplied by the AC-DC Power Supply  110  across the various requests from multiple Devices  200 ( 1 )- 200 ( n ).  FIG. 8  illustrates that the last Device  200 ( n ) was refused power, as indicated by indicator  101 , because its request exceeded the Source&#39;s ability to provide it.  
         [0088]     In another embodiment, as illustrated in  FIG. 9 , a Universal Splitter or Bridge  900  may be connected to and communicate with a Source  100  as any other Device would. In turn, the Bridge  900  then uses the power from the Source  100  to supply multiple Devices  200 ( i )- 200 ( n ). Any Device plugged into the Bridge  900  would see the Bridge  900  as any other Universal Source  100 .  
         [0089]     In one embodiment, the Bridge  900  may request the maximum voltage possible (for example, 27V). The Bridge  900  would either pump that voltage up to a level greater than or equal to 32V to supply a full range of voltages to its Devices  200 ( i )- 200 ( n ), or it would simply deny power to any Device that requested above what it could provide (about 23-24V). The Bridge  900  would also be required to budget the maximum average and peak currents that it requested from the Source  100  to its Devices  200 ( i )- 200 ( n ).  
         [0090]     Having described exemplary embodiments of the invention, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. Therefore, it is to be understood that changes may be made to embodiments of the invention disclosed that are nevertheless still within the scope and the spirit of the invention as defined by the appended claims.