Abstract:
Circuitry and techniques for managing a power supply are disclosed. A processor-controlled switch is employed to control the delivery of power to conductors that provide power to an external electronic device wherein the processor controls the switch opening and the switch opening based not only on contemporaneous parameter measurements but also on state information known to the processor. The management circuit can control the power supply without requiring the use of an additional sense wire between the management circuit and the external electronic device.

Description:
BACKGROUND  
       [0001]     Power supplies have long been employed to provide power to electronic devices. For example, most electronic devices require some type of power adaptor arrangement to transform household voltages (e.g., 110 V or 220 V) to the voltage level(s) suitable for charging the batteries and/or operating the electronic components.  
         [0002]     As power adaptor design evolves, the design has become more user-friendly over time. Most power adaptors nowadays enclose the power electronics and/or electrical circuitry in a power adaptor housing. The power electronics and/or electrical circuitry within the power adaptor housing performs the voltage/current transformation tasks to provide the suitable voltage levels for device operation. These voltages/currents are then provided to the electronic device (e.g., a laptop computer or a digital audio/video player) via flexible electrical conductors. The flexible electrical conductors are coupled to pins of a connector plug that is configured to be mated with a corresponding socket in the electronic device.  
         [0003]     This arrangement substantially minimizes the impact on the portability of the electronic device while power is plugged in. For example, a laptop user may continue to move the laptop computer around while being plugged in with relative ease since the laptop is connected to a flexible conductor cable and the bulk of the power electronics of the power adaptor is advantageously disposed further away from the laptop (e.g., on the floor).  
         [0004]     Power adaptors have also evolved to the point where management circuitry is provided to monitor the operation of the power electronics and to respond if changing, dangerous and/or undesirable operating conditions exist. For example, the management circuitry of some power adaptors may allow the adaptor to cease providing power to the electronic device if the power adaptor overheats, for example.  
         [0005]     As users demand more and more sophistication from their electronic devices and accessories, management circuitries and techniques for power supplies continue to improve. This patent application relates to novel and innovative arrangements and techniques for managing power supplies.  
       SUMMARY  
       [0006]     The following presents a simplified summary of some embodiments of the invention in order to provide a basic understanding of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the more detailed description that is presented below.  
         [0007]     The invention relates, in an embodiment, to a management circuit (MC) for a power supply, the power supply being configured to supply a first voltage level and a ground voltage level. The management circuit includes a first MC terminal coupled to a positive supply terminal of the power supply, the positive supply terminal being configured to provide the first voltage level. The management circuit further includes a second MC terminal coupled to a ground terminal of the power supply, the ground terminal being configured to provide the ground voltage level. The management circuit additionally includes a switch and a processor coupled to the switch for controlling the switch. The management circuit also includes a first output terminal, the switch being coupled to the first MC terminal and the first output terminal for controllably providing the first voltage level to the first output terminal. There are also included a first impedance circuit coupled to the second MC terminal and a second output terminal coupled to the first impedance circuit, wherein the processor controls the switch opening and the switch closing responsive to both parameters sensed through the first output terminal and the second output terminal and previous state information pertaining to a present operating state of the management circuit.  
         [0008]     In another embodiment, the invention relates to a method for controlling a power supply, the power supply being configured to supply a first voltage level and a ground voltage level. There is included providing a management circuit having a processor coupled to a switch, the switch being coupled between a first output terminal of the management circuit and a positive supply terminal of the power supply that provides the first voltage level. The processor controls switch opening and switch closing of the switch to respectively break and make a conduction path between the first output terminal and the positive supply terminal. The method also includes providing a impedance circuit coupled between a ground terminal of the power supply that supplies the ground voltage level and a second output terminal of the management circuit, whereby the first output terminal and the second output terminal representing respectively a power conductor and a ground conductor configured to provide the first voltage level and the ground voltage level respectively to an electronic device when the electronic device is coupled to the management circuit. The method additionally includes monitoring voltages obtained at at least one of the first analog sense node and the second analog sense node using the processor, wherein the voltages at the first sense node and the second sense nodes are derived from one of voltage and current obtained from the first output terminal and the second output terminal, the processor controlling the switch opening and the switch opening based at least on the voltages obtained at the at the at least one of the first analog sense node and the second analog sense node and previous state information pertaining to a present operating state of the management circuit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:  
         [0010]      FIG. 1  shows a schematic diagram of a power supply and a power management circuit, in accordance with an embodiment of the present invention.  
         [0011]      FIG. 2  shows a flow chart describing the steps/actions taken in the disconnected state, in accordance with an embodiment of the present invention.  
         [0012]      FIG. 3  shows a flow chart describing the steps/actions taken in transitioning from the disconnected state to the connected state, in accordance with an embodiment of the present invention.  
         [0013]      FIG. 4  shows a flow chart describing the steps/actions taken while performing “on” status checks, in accordance with an embodiment of the present invention.  
         [0014]      FIG. 5  shows a flow chart describing the steps/actions taken to shut down the power source, in accordance with an embodiment of the present invention.  
         [0015]      FIG. 6  shows a flow chart describing the steps/actions taken in testing for the low-power scenario or the decoupling scenario, in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0016]     The present invention will now be described in detail with reference to a few embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.  
         [0017]     Various embodiments are described hereinbelow, including methods and techniques. It should be kept in mind that the invention might also cover articles of manufacture that includes a computer readable medium on which computer-readable instructions for carrying out embodiments of the inventive technique are stored. The computer readable medium may include, for example, semiconductor, magnetic, opto-magnetic, optical, or other forms of computer readable medium for storing computer readable code. Further, the invention may also cover apparatuses for practicing embodiments of the invention. Such apparatus may include circuits, dedicated and/or programmable, to carry out tasks pertaining to embodiments of the invention. Examples of such apparatus include a general-purpose computer and/or a dedicated computing device when appropriately programmed and may include a combination of a computer/computing device and dedicated/programmable circuits adapted for the various tasks pertaining to embodiments of the invention.  
         [0018]      FIG. 1  is a schematic representation of a power protection circuit (PPC)  100  in accordance with an embodiment of the present invention.  FIG. 1  shows a power supply (PS)  102 , representing a direct current power source having a negative terminal  102   a  and a positive terminal  102   b , and a shut-down terminal  102   c . Power supply terminals  102   b  and  102   a  supply power and ground respectively to operate PPC  100  and an electronic device  150  if the electronic device is coupled to PPC  100 . Shut-down terminal  102   c  is configured to receive a shut-down signal from a processor  104  of PPC  100  to shut down power supply  102  in case there is a fault condition, for example.  
         [0019]     Power supply  102  may represent, for example, a power adapter that transforms household voltages (e.g., 110V or 220V) to voltage and current levels suitable for operating PPC  100  and electronic device  150  in accordance with user specification. In the example of  FIG. 1 , electronic device  150  represents a laptop computer although electronic device  150  may represent any power consuming electronic device, whether or not equipped with a battery.  
         [0020]     Positive supply terminal  102   b  is shown coupled to a processor-controlled switch  126 , which opens and closes responsive to a control signal from processor  104  to respectively break and make electrical contact with a node  140 . Node  140  is coupled to a pin (not shown) in a connector  108  to transmit power to a node  160  of electronic device  150  when power supply  102  is turned on, switch  126  is closed, and electronic device  150  is coupled to PPC  100 . A node  142  at the bottom of  FIG. 1  provides a grounding path for circuitry within electronic device  150  when connector  108  of PPC  100  and connector  110  of electronic device  150  are coupled together. Nodes  140  and  142  represent, for example, the wired conductors that are employed to carry power and ground from the circuitry bulk of the power adapter to the plug that is mated with the laptop computer. The components of PPC  100  may be integrated within the power adapter housing that also houses power supply  102 , in an embodiment.  
         [0021]     In parallel with switch  126  is an impedance circuit  114 , represented in the example of  FIG. 1  by a resistor R 1 . As will be discussed later herein, impedance circuit  114  along with impedance circuit  116  (represented by a resistor R 2  in the example of  FIG. 1 ), impedance circuit  118  (represented by a resistor R 3  in the example of  FIG. 1 ), and impedance circuit  120  (represented by a resistor R 4  in the example of  FIG. 1 ) operate cooperatively with power supply  102 , switch  126 , and a differential amplifier  106  to provide sensing voltage levels to analog input nodes  144  and  146  of processor  104 . These voltage levels enable processor  104  to ascertain the operating conditions of power supply  102  and electronic device  150 . These operating conditions in turn enable processor  104  to appropriately operate switch  126  and/or power supply  102  to deliver or cut off power to node  140 .  
         [0022]     The operation of PPC  100  may be better understood with reference to a few simple example scenarios below. For even more detailed information, discussions of various example scenarios are also discussed in connection with the flowcharts provided with other figures herein.  
         [0023]     The first scenario represents the default situation wherein connector  108  is unconnected, i.e., not coupled to electronic device  150  or any other device. In this case, PPC  100  is said to be in the “unconnected” state, and it is desirable to turn off power to pin  140  to prevent an accidental shorting of the pins of connector  108  from creating sparks and/or damage PPC  100  and/or damage power supply  102 .  
         [0024]     In the default scenario (which also represents a typical starting condition for PPC  100 ), switch  126  is open, thereby effectively interrupting the low-impedance path from positive supply terminal  102   b  to node  140 . Since connector  108  is also disconnected from connector  110  of electronic device  150 , no current flows through resistor R 4 , thereby resulting in no voltage difference across resistor R 4 . Differential amplifier  106  (which may represent a stand-alone component or may be integrated with other components such as within processor  104 ) senses the current flowing through resistor R 4  (as reflected by the potential difference across R 4 ) and provides an analog input to processor  104  via sense node  146 . In this case, the analog input at sense node  146  will be essentially zero to reflect the fact that no current flows through resistor R 4 .  
         [0025]     The voltage at sense node  144  is determined by the voltage dividing circuit comprising resistors R 1 , R 2 , and R 3  and reflects a value characteristic of the unplugged state. As long as the voltage at sense node  144  stays within the value range characteristic of the unplugged state (referred to herein as the “unplugged voltage range”), processor  104  keeps switch  126  open.  
         [0026]     The second scenario relates to the situation wherein connector  108  of PPC  100  was previously unconnected but is now connected to connector  110  of electronic device  150 . Further, assume that both PPC  100  and electronic device  150  operate normally (i.e., there are no fault conditions in either PPC  100  or electronic device  150 ). In this case, it is desirable to deliver power from power supply  102  to electronic device  150  after it is ascertained that the coupling between connector  108  and electronic device  150  is satisfactory.  
         [0027]     Starting from the default unplugged state discussed above, the coupling of connector  108  to electronic device  150  changes the impedance seen by nodes  140  and  142 . Even though switch  126  remains open at this point in time, the voltage value at sense node  144  changes due to the fact that an impedance load characteristic of electronic device  150  has now been placed in parallel with resistors R 2 -R 3 . The voltage value at sense node  144  will be in the range (referred to herein as the “good connection voltage range”) that reflects the fact that an impedance load characteristic of electronic device has been coupled to nodes  140  and  142 .  
         [0028]     This voltage value in the “good connection voltage range” is detected by processor  104  (which reads the voltage value at sense node  144 ) and results in the processor recognizing that PPC  100  is now coupled with electronic device  150 . This recognition causes processor  104  to close switch  126  to cause power to be delivered to node  140  from power supply terminal  102   b . For robustness, processor  104  may require that the voltage at sense node  144  stays within the “good connection voltage range” for a given amount of time before switch  126  is closed. This time delay eliminates the possibility that transient voltages at sense node  144  may inadvertently cause processor  104  to close switch  126 . Note that if the voltage at sense node  144  is outside of this characteristic range, the processor would not recognize that PPC  100  is now coupled with electronic device  150  and would not cause switch  126  to be closed.  
         [0029]     PPC  100  is now in the connected state, and the voltage at sense node  146  and/or sense node  144  are monitored for other scenarios. Note that in this connected state, the current through R 4  will be higher than in the unplugged state, causing differential amplifier  106  to sense the larger voltage difference across R 4 . As will be discussed later herein, the sensed voltage difference across R 4  is employed to ascertain the transition to other operating states from the connected state.  
         [0030]     The next example relates to the situation wherein the voltage difference across resistor R 4  drops. This voltage difference across R 4  may drop due to diminished current through resistor R 4 , which in turn may be due to, for example, either the “low power” scenario or the “decoupling” scenario.  
         [0031]     In the “low-power” scenario, the user may have turned off the laptop computer while leaving the power adapter plugged in. In this case, the user may for example wish to continue to trickle charge the battery of the laptop as needed to prevent a “brown-out” condition. As another example, certain electronic device continues to have a portion of their circuitry operating in the low-power mode (e.g., sleep or hibernate or watch-dog circuitry). In these cases, the appropriate action is to continue supplying power to node  140  even though processor  104  may have sensed at sense node  146  that the current through R 4  has dropped.  
         [0032]     Alternatively, in the “decoupling” scenario, the user unplugs connector  108  from connector  110 . In this case, it is desirable to interrupt power delivery to node  140  from positive supply terminal  102   b  by opening switch  126 .  
         [0033]     In an embodiment, both the low-power scenario and the decoupling scenario are first detected when the current through resistor R 4  drops below a certain “connection” threshold. In other words, as soon as the voltage at sense node  146  drops below the “connection” threshold (typically some small voltage level above zero), processor  104  deems that the connected state is terminated and PPC  100  may be transitioning to either the low-power scenario or the decoupling scenario.  
         [0034]     The low-power scenario is ascertained and handled as follows. Upon detecting that the current through resistor R 4  has dropped below the “connection” threshold (as evidenced by the voltage across R 4 , which is sensed by processor  104  via differential amplifier  106 ), processor  104  commands switch  126  to open to interrupt the flow of current from positive supply terminal  102   b  into node  140 . The opening of switch  126  causes the voltage at node  140  to drop from the high voltage level that existed when switch  126  was closed. The decay of the voltage level at node  140  also causes the voltage level at sense node  144  to decay. The decay at sense node is then monitored by processor  144 . In an embodiment, the level or rate of decay or pattern of decay may be monitored. Generally speaking, processor  144  has internal memory or access to memory to stores in advance information such as expected voltage levels of various states/scenarios, expected decay rate, expected plot of voltage and/or current versus time, voltage thresholds, timer duration, etc.  
         [0035]     If the voltage at sense node  144  is characteristic of a PPC that transitions from a connected state to a low-power state (e.g., in the case where the user turns off the laptop computer but leaves the laptop computer connected to PPC  100 , thereby reducing the current draw but leaving the system impedance of electronic device  150  connected across nodes  140  and  142 ), processor  104  turns on switch  126  to allow power delivery to resume to node  140 . This permits, as mentioned earlier, power to be delivered to the laptop computer to, for example, prevent a “brown-out condition” or keep some small watch-dog circuits active. In an embodiment, a small delay may be built-in (via a timer, for example) between the cycles of sensing the drop at sense node  144  and turning on switch  126  so that switch  126  is not needlessly cycled on and off rapidly. For example, a delay may be provided such that the maximum off-and-on switch rate of switch  126  is about 3 times a second during the “low-power” state.  
         [0036]     If, however, the voltage at sense node  144  is characteristic of a PPC that transitions from a connected state to a disconnected state (e.g., in the case where the user unplugs the laptop computer from the PPC  100 , thereby removing the system impedance of electronic device  150  from nodes  140  and  142 ), processor  104  keeps switch  126  off after the voltage at sense node  144  stays above the “connection” threshold after a period of time. This is a desirable result to keep power from being delivered to the pins of an unplugged power adapter.  
         [0037]     Another scenario relates to the case wherein the pins of connector  108  are shorted when switch  126  is off. As expected, this should not cause any damage since no appreciable amount of power is delivered to node  140  when switch  126  is turned off. However, since there is current flowing through the R 1 -R 2 -R 3  loop, as well as through the R 1 -shorted pins-R 4  loop, an analysis is provided for completeness. Resistor R 4  is typically much smaller than resistor R 1 . For example, resistor R 4  may be in the range of milli-ohms such as 10 milli-ohms in an embodiment. As a further example, resistor R 1  may be in the range of kilo-ohms, such as about 150 kilo-ohms in an embodiment. In this case, most of the voltage drop in the R 1 -shorted pins-R 4  loop will be across resistor R 1  when the pins of connector  108  are shorted, causing the voltage level at node  140  to drop to nearly zero.  
         [0038]     This near-zero voltage at node  140  is reflected at sense node  144  due to the voltage divider circuit of loop R 1 -R 2 -R 3  and sensed by processor  104 . Since the low voltage at sense node  144  is lower than the aforementioned “good connection voltage range,” processor  104  does not turn on switch  126 . In fact, even if transient conditions during the shorting process causes the voltage at node  144  to happen to be in the aforementioned “good connection voltage range,” it is highly unlikely that this transient condition would stay stable long enough to satisfy the stable time requirement imposed by the delay clock. If the voltage at sense node  144  does not stay in the aforementioned “good connection voltage range” for the requisite time period imposed by the delay clock, processor  104  does not turn on switch  126 .  
         [0039]     Another scenario relates to the case wherein connector  108  is plugged into an electronic device but a short occurs after switch  126  is closed. In other words, the short is experienced after power is delivered to node  140  (and to any connected electronic device). In this case, it is desirable to immediately turn off switch  126  (and optionally to immediately turn off power supply  102 ) to prevent further damage.  
         [0040]     After connector  108  is plugged into the electronic device and switch  126  is closed, the voltage drop across resistor R 4  is watched by processor  104  via differential amplifier  106  as mentioned. If the current through resistor R 4  exceeds a first “dangerous” threshold level for a certain time period (which high current condition is reflected in the large voltage difference across R 4  and sensed by processor  104  via amplifier  106  and node  146 ), processor  104  opens switch  126  and turns off power supply  102  (by issuing a command via terminal  102   c ).  
         [0041]     In an embodiment, a second, “critical” threshold that is higher than the “dangerous” threshold may be established. If the current through resistor R 4  exceeds the critical threshold level (which critical current condition is reflected in the larger voltage difference across R 4  and sensed by processor  104  via amplifier  106  and node  146 ), processor  104  immediately opens switch  126  and immediately turns off power supply  102  (by issuing a command via terminal  102   c ) substantially without any delay.  
         [0042]     In this manner, a persistent and dangerous high current fault condition will cause switch  126  to be opened and power supply  102  to be turned off after some time. A critical high current fault condition will cause switch  126  to be immediately opened and power supply  102  to be immediately turned off.  
         [0043]     Alternatively or additionally, the voltage at sense node  144  may also be monitored. In an embodiment, if the voltage at sense node  144  stays below a first shut-off voltage threshold for a given period of time, processor  104  opens switch  126  and turns off power supply  102  (by issuing a command via terminal  102   c ). In an embodiment, if the voltage at sense node  144  falls below a second shut-off voltage threshold that is lower than the first shut-off voltage threshold, processor  104  immediately opens switch  126  and immediately turns off power supply  102  (by issuing a command via terminal  102   c ) substantially without any delay.  
         [0044]      FIG. 2  is an illustrative flowchart of a method of monitoring a power circuit in accordance with an embodiment of the present invention. At a first step  202 , the method assumes that the PPC is disconnected from an electronic device. At a next step  204 , switch  126  (see  FIG. 1 ) is turned off or opened. As noted above, when switch  126  is opened and PPC  100  is unconnected to the electronic device, no power is delivered to node  140 . However, current still flows through the R 1 -R 2 -R 3  loop, allowing processor  104  to monitor the voltage level at sense node  144  (step  206 ). In some embodiments, the frequency of monitoring occurs at approximately 1,000 hertz although other suitable monitoring frequencies are also possible.  
         [0045]     If, as shown in step  208 , the voltage at sense node  144  enters into the range R 1  (e.g., the aforementioned “good connection voltage range”), the method proceeds to step  302  wherein operating parameters/conditions of the PPC are tested to determine the appropriate action(s) to be taken next. On the other hand, if the voltage at sense node  144  stays outside of this range, the PPC remains in the disconnected state, and the method returns from step  208  to step  206  to continue to monitor the voltage at sense node  144 .  
         [0046]      FIG. 3  is an illustrative flowchart of a method of protecting a power circuit when the PPC transitions out of the disconnected state, in accordance with an embodiment of the present invention. Generally speaking, after the voltage at sense node  144  enters the voltage range R 1  (e.g., the aforementioned “good connection voltage range”), the steps of FIG.  3  ascertain whether the voltage at sense node  144  stays stable within the range for a predefined time period (determined by a timer T 1 ) or is a transient condition. If the voltage at sense node  144  stays stable within the voltage range R 1  for a predefined time period (determined by a timer T 1 ), switch  126  is turned on to deliver power to node  140 . On the other hand, if the voltage at sense node  144  does not stay stable within the range R 1  for a predefined time period, transients are deemed to be the cause for the fluctuation of the voltage level at sense node  144 , and the PPC transitions back to the disconnected state of  FIG. 2  without turning on switch  126 .  
         [0047]     Thus, at step  302 , the power supply  102  is shown to be on but switch  126  remains off. Step  302  is arrived at from step  208  of  FIG. 2  when the voltage at sense node  144  enters the voltage range R 1  (e.g., the aforementioned “good connection voltage range”). In this case, the voltage at sense node  144  is continued to be monitored (step  304 ). If the voltage at sense node  144  stays in the voltage range R 1 , the method checks to see if the stable period requirement has been satisfied (steps  310 ,  312 , and  314 ). Thus, in step  310  and  312 , the timer is started if a timer has not been started. After the timer is started (step  312 ) or if the timer has already started (yes branch of step  310 ), the method checks at step  314  to determine whether the timer has expired.  
         [0048]     If the timer has expired while the voltage at sense node  144  stays within the voltage range R 1  (yes branch of step  314 ), the operating state of the PPC is deemed to be the connected state ( 316 ), and switch  126  is then turned on ( 318 ). Thereafter, the method monitors the voltage at one or both of sense nodes  144  and  146  to monitor the operating status. This monitoring will be discussed later herein.  
         [0049]     On the other hand, if the timer has not expired while the voltage at sense node  144  stays within the voltage range R 1  (no branch of step  314 ), the method returns from step  314  to step  304  to continue to monitor the voltage at sense node  144 .  
         [0050]     Note that if the voltage at sense node  144  drops outside of the voltage range R 1  before the timer expires, the timer is stopped and reset (no branch of step  306  and step  308 ), and the method returns to the disconnected state of step  202  of  FIG. 2 .  
         [0051]      FIG. 4  is an illustrative flowchart of the “ON” status checks (step  320 ), in accordance with an embodiment of the present invention. Generally speaking, steps  402 ,  404 ,  406 ,  408 , and  410  ascertain whether a dangerous or critical current condition has occurred while the PPC is in the connected state and switch  126  is closed. Steps  414 ,  416 ,  418 , and  420  check to see whether a low voltage condition seen across resistor R 4  represents a dangerous/critical situation, the “low power” scenario (e.g., the user turns off the laptop computer but leaves the power adapter plugged in) or the “decoupling” scenario (e.g., the user disconnects the laptop computer from the power adapter).  
         [0052]     At step  402 , the current through resistor R 4  is checked (by processor  104  via node  146  and differential amplifier  106 ) to see whether that current exceeds a critical threshold CT 1 . If the current through resistor R 4  exceeds this critical threshold CT 1 , the method proceeds to step  502  of  FIG. 5  to immediately turn off all timers (step  502  of  FIG. 5 ) and to turn off the power supply  102  (step  504  of  FIG. 5 ). Alternatively or additionally, the processor may also open switch  126 . Thereafter, the method returns from step  504  of  FIG. 5  to step  202  of  FIG. 2  (representing the disconnected state).  
         [0053]     At step  404  (from the no branch of step  402 ), it is ascertained whether the current through resistor R 4  exceeds a lesser but potentially dangerous threshold. If not (no branch step  404 ), the method proceeds to step  412  to begin checking to see whether a low voltage condition exists at sense node  144 . As mentioned, the low voltage condition at sense node  144  may exist due to, for example, a short that occurs when power is being delivered. Note that this check (steps  412 ,  414 ,  416 ,  418 , and  420 ) is shown in series with the high current check of steps  402 - 412 . In practice, these two checks may be made in parallel if desired.  
         [0054]     Returning to step  404 , if on the other hand the current through resistor R 4  exceeds a lesser but potentially dangerous threshold, the method proceeds to one or more of steps  406 ,  408 ,  410 , and  412  to check whether the dangerous but non-critical current condition persists longer than a predefined time (as measured by timer T 2 ). Thus, in step  406  and  408 , timer T 2  is started if timer T 2  has not been started. After timer T 2  is started (step  408 ) or if timer T 2  has already started (yes branch of step  406 ), the method checks at step  410  to determine whether timer T 2  has expired.  
         [0055]     If timer T 2  has expired while the current through resistor R 4  remains above the dangerous threshold “TIMED CURRENT THRESHOLD,” (yes branch of step  410 ), the method proceeds to step  502  of  FIG. 5  to turn off all timers (step  502  of  FIG. 5 ) and to turn off the power supply  102  (step  504  of  FIG. 5 ). Alternatively or additionally, the processor may also open switch  126 . Thereafter, the method returns from step  504  of  FIG. 5  to step  202  of  FIG. 2  (representing the disconnected state).  
         [0056]     As mentioned, one or more of steps  412 ,  414 ,  416 ,  418 , and  420  implements the low voltage condition check for the voltage at sense node  144 . The voltage at sense node  144  may become critically low if, for example, there exists a short between terminals  140  and  142  after connector  108  is plugged in and power is being delivered to terminal  140 . In step  412 , the voltage at sense node  144  is checked (by processor  104 ) to see whether that voltage drops below a critical voltage threshold VT 1 . In an embodiment, VT 1  may be, for example, 0.5V. If the voltage at sense node  144  falls below the critical voltage threshold VT 1 , the method proceeds step  502  of  FIG. 5  (yes branch of step  412 ) to immediately turn off all timers (step  502  of  FIG. 5 ) and to turn off the power supply  102  (step  504  of  FIG. 5 ). Alternatively or additionally, the processor may also open switch  126 . Thereafter, the method returns from step  504  of  FIG. 5  to step  202  of  FIG. 2  (representing the disconnected state).  
         [0057]     At step  414  (from the no branch of step  412 ), it is ascertained whether the voltage at sense node  144  falls below a higher-than-critical but still potentially dangerously low voltage threshold TIMED VOLTAGE THRESHOLD. This situation may happen, for example, if a defect in power supply  102  causes power supply  102  to output a dangerously low voltage.  
         [0058]     If the voltage at sense node  144  falls below the higher-than-critical but still potentially dangerously low voltage threshold TIMED VOLTAGE THRESHOLD, a timer is watched to determine if the voltage at sense node  144  stays below this threshold for longer than a predetermined time period (determined by timer voltage T 3 ). This watch is performed by steps  416 ,  418 , and  420 . Thus in step  418 , if timer T 3  has not started (no branch of step  416 ), timer T 3  is started. If timer T 3  has started (yes branch of step  416 ), step  420  checks to see if voltage timer T 3  has expired. If voltage timer T 3  expired while the voltage at sense node  414  remains under the higher-than-critical but still potentially dangerously low voltage threshold TIMED VOLTAGE THRESHOLD, the method proceeds to step  502  of  FIG. 5  (yes branch of step  420 ) to turn off all timers (step  502  of  FIG. 5 ) and turn off the power supply  102  (step  504  of  FIG. 5 ). Alternatively or additionally, the processor may also open switch  126 . Thereafter, the method returns from step  504  of  FIG. 5  to step  202  of  FIG. 2  (representing the disconnected state).  
         [0059]     Returning to step  414 , if voltage at sense node  144  does not fall below the higher-than-critical but still potentially dangerously low voltage threshold TIMED VOLTAGE THRESHOLD, the PPC is operating normally and the method proceeds to step  602  of  FIG. 5  to begin checking whether a low current condition exists across resistor R 4 . As mentioned, this low current condition may be indicative of either a “decoupling” scenario (e.g., the user disconnects the power adapter from the laptop computer) or a “low-power” scenario (e.g., the user turns off the laptop computer but leaving the power adaptor plugged in.  
         [0060]     Thus, in step  602  of  FIG. 6 , the current through resistor R 4  is monitored (by processor  104  via differential amplifier  106  and node  146 ) to ascertain whether this current drops below a current threshold CT 2  (e.g., minimum current output by power supply for an operational laptop in an embodiment). If the current through resistor R 4  stays above current threshold CT 2 , the system is deemed to operate normally in which case the method returns to step  320  of  FIG. 3  (yes branch of step  602 ) to back to continue “on” status checks.  
         [0061]     On the other hand, if the current through resistor R 4  falls below the current threshold CT 2  (no branch of step  602 ), the method proceeds to ascertain whether the low current condition through resistor R 4  is indicative of a “decoupling” scenario or a “low-power” scenario. In step  604 , a low power timer is started. In step  606 , switch  126  is turned off. In steps  608 - 612 , the method monitors the voltage level at sense node  144  (which steady-state level and/or rate of decay depends on whether the system impedance of the electronic device is still seen by terminals  140  and  142 ).  
         [0062]     If the voltage at sense node  144  stays above a voltage threshold VT 2  for longer than a time period determined by a low power timer, the “decoupling” scenario is deemed to have occurred. This voltage threshold VT 2  for sense node  144  is selected to be the voltage threshold that discriminates between the case where the laptop is still connected to the power adapter but the laptop is turned off and the case where the laptop is disconnected from the power adapter. In the case where sense node  144  stays above a voltage threshold VT 2  for longer than the low power period (no branch of step  610  and yes branch of step  612 ), the method proceeds to step  202  of  FIG. 2  to start operating from the disconnected state again.  
         [0063]     Returning to step  610 , if the voltage at sense node is below the voltage threshold VT 2  (yes branch of step  610 ), the method proceeds to step  316  of  FIG. 3  to turn switch  126  back on (since switch  126  was turned off in step  606 ). In this case, the processor  104  has determined that the electronic device is turned off but still plugged in (i.e., its characteristic impedance is still seen by terminals  140  and  142  and still affecting the rate of decay at node  140  and sense node  144  after switch  126  is turned off). Turning the switch  126  back on in step  316  of  FIG. 3  allows the PPC to begin the “on” status checks again (since switch  126  is closed even if a high operating current is not presently required by the dormant-but-plugged-in electronic device  150 ).  
         [0064]     As can be appreciated from the foregoing, embodiments of the invention permit various operating conditions of the power supply to be accurately monitored and appropriate actions to be rapidly and appropriately taken with respect to different operating scenarios and operating states. Embodiments of the invention rely not only on contemporaneous measurements of electrical parameters to perform its power supply managing tasks (as would be the case with an analog controller) but also on present state information (i.e., the state the PPC is currently in before switching to the next state) and the voltage level/pattern information received at sense nodes  144  and  146  to more accurately and rapidly perform its tasks.  
         [0065]     Advantageously, embodiments of the invention employ the power and ground conductors for its monitoring tasks. In this sense, it may be said that the voltage information that exist on analog sense node  144  and analog sense node  146  is obtained through (i.e., derivative of or deriving from) voltage and/or current at/on/through terminals  140  and  144  (which are the power conductor and the ground conductor that supply power voltage level and ground voltage level to the electronic device), thereby eliminating the need for a separate sense wire/conductor between the circuitry of the PPC and the circuitry of the electronic device and/or the circuitry of the power supply  
         [0066]     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. For example, impedance circuit values and timer values as described herein are highly dependent on the power source specification and the specification of the electronic device, as well as design choices. The impedance circuits may be implemented by resistors or any other suitable impedance arrangements. The power supply may represent a power supply that transforms one voltage level to another or may simply representing a non-transforming (i.e., not translating from one voltage level to another voltage level) power supply. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.