Abstract:
A current control circuit receives a power supply voltage on a supply node and is coupled between the supply node and a storage node that is coupled to an energy storage circuit. The current control circuit is operable in a charging mode to limit a current supplied from the supply node to the storage node and operable in a discharge mode to instantaneously supply current to the supply node from the storage node responsive to a voltage on the supply node being less than a threshold value.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to electronic circuits, and more specifically to limiting charging current and controlling discharge current of energy storage devices in electronic circuits.  
       BACKGROUND OF THE INVENTION  
       [0002]     Every electronic device needs some source of electrical power to function. A typical computer system, for example, includes a power supply that is plugged into an alternating current (AC) outlet and generates direct current power at required voltages to power components in the system. In many electronic systems, such as a typical computer system or a computer network, even a momentary loss of power can result in a significant disruption for users of the system or network. For example, if AC power to a conventional computer system is lost even for only a few seconds, the system may reset and documents on which a user of the system was working may be lost. As a result, many computer systems and networks include backup power supplies to prevent disruption and loss of documents in the event of a failure of AC power.  
         [0003]      FIG. 1  is a functional block diagram illustrating an electronic device  100  including conventional power control circuitry  102  that controls power supplied to logic circuitry  104 , which includes logic to perform desired functions of the device. An internal power supply  106  supplies an internal supply voltage VIPS to the circuitry  102  and the circuitry also receives an external supply voltage VEPS from an external power source (not shown). A capacitor bank  108  includes a plurality of capacitors (not shown) coupled in parallel, with these capacitors being charged by the power control circuitry  102  to provide a backup source of power that is primarily utilized when switching between the supply voltages VEPS and VIPS.  
         [0004]     In operation, the power control circuitry  102  applies either the internal power supply voltage VIPS or the external power supply voltage VEPS as a supply voltage VS to the logic circuitry  104 . In normal operation, the power control circuitry  102  applies the internal supply voltage VIPS to the logic circuitry  104  as the supply voltage VS and isolates the external supply voltage VEPS from the logic circuitry. The circuitry  102  also charges the capacitor bank  108  using the internal supply voltage VIPS during this mode of operation. The power control circuitry  102  also monitors the internal supply voltage VIPS to determine whether this voltage is greater than a threshold value. In the event the internal power supply  106  fails and the internal supply voltage VIPS drops below the threshold value, the control circuitry  102  isolates the internal power supply  106  from the logic circuitry  104  and then couples the capacitor bank  108  to the logic circuitry  104  to provide the supply voltage VS. The control circuitry  102  thereafter provides the external supply voltage VEPS as the supply voltage VS to provide power to the logic circuitry  104 .  
         [0005]     The function of the power control circuitry  102  is to ensure that adequate power is provided to the logic circuitry  104  even when the internal power supply  106  fails. To perform this function, the power control circuitry  102  must include control circuitry (not shown) to detect a failure of the internal power supply and switching components such as relays (not shown) to couple the appropriate power source, namely the supply voltages VEPS, VIPS or the capacitor bank  108 , to the logic circuitry  104 . The control circuitry and switching components result in the power control circuitry  102  typically requiring relatively complex circuitry to implement. This is true because the circuitry  102  must operate very quickly to ensure that the supply voltage VS does not drop below a minimum threshold level required to ensure proper operation of the logic circuitry  104 . For example, if the power control circuitry  102  does not quickly detect the failure of the internal power supply  106  then the supply voltage VS may drop below this minimum threshold value prior to the circuitry coupling the capacitor bank  108  to the logic circuitry  104 . Similarly, if the power control circuitry  102  does not thereafter quickly provide the external supply voltage VEPS to the logic circuitry  104 , the energy stored in the capacitor bank  108  may be insufficient to maintain the supply voltage VS above the required minimum threshold. Either of these situations could result in erroneous operation or reset of the logic circuitry  104 , which adversely affects the operation of the electronic device  100 . This relative complexity of the circuitry and components required to implement the power control circuitry  102  also occupies valuable space within the electronic device  100  and also increases the cost of producing the electronic device.  
         [0006]     There is a need for power control circuitry that operates extremely quickly while requiring relatively simple components and circuitry to implement.  
       SUMMARY OF THE INVENTION  
       [0007]     According to one aspect of the present invention, a current control circuit is adapted to receive a power supply voltage on a supply node and is coupled between the supply node and a storage node adapted to be coupled to an energy storage circuit. The current control circuit is operable in a charging mode to limit a current supplied from the supply node to the storage node and operable in a discharge mode to instantaneously supply current to the supply node from the storage node responsive to a voltage on the supply node being less than a threshold value. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a functional block diagram of an electronic device including conventional power control circuitry for controlling power supplied to logic circuitry in the device.  
         [0009]      FIG. 2  is a functional diagram and schematic illustrating a power control circuit according to one embodiment of the present invention.  
         [0010]      FIG. 3  is a functional diagram of a computer network including an Ethernet switch containing a power switching and control circuit including the power control circuit of  FIG. 2 .  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0011]      FIG. 2  is a functional block diagram of a power control circuit  200  that operates to instantaneously provide power to maintain a supply voltage VS above a minimum threshold value in the event an internal supply voltage VIPS fails and prior to an external supply voltage VEPS being output as the supply voltage. More specifically, the power control circuit  200  includes a current control circuit  202  that instantaneously supplies current from a capacitor bank  204  to maintain the supply voltage VS above the minimum threshold for the time period between the detection of the failure of the internal supply voltage VIPS and the external supply voltage VEPS being output as the supply voltage, as will be explained in more detail below.  
         [0012]     Many of the specific details of certain embodiments of the invention are set forth in the following description and accompanying figures to provide a thorough understanding of such embodiments. One skilled in the art will understand, however, that the present invention may be practiced without several of the details described in the following description. Moreover, in the description that follows, it is understood that the figures related to the various embodiments are not to be interpreted as conveying any specific or relative physical dimensions, and that specific or relative physical dimensions, if stated, are not to be considered limiting unless the claims expressly state otherwise. Further, illustrations of the various embodiments when presented by way of illustrative examples are intended only to further illustrate certain details of the various embodiments, and shall not be interpreted as limiting the scope of the invention.  
         [0013]     The power control circuit  200  further includes a switching circuit  206  including a first switch SW 1  that selectively applies the internal supply voltage VIPS to a supply node  208  in response to a switch control signal SC. The supply node  208  is a node on which the supply voltage VS is provided to power electronic components (not shown). The switching circuit  206  further includes a second switch SW 2  that selectively applies the external supply voltage VEPS to the supply node  208  responsive to the switch control signal SC. The capacitor bank  204  includes a number of capacitors C 1 -CN coupled in parallel which develop a capacitor bank voltage VCB on a storage node  210 .  
         [0014]     The current control circuit  202  includes a current limiting element  212  coupled between the supply node  208  and the storage node  210  to provides a current from the supply node to the storage node  210  to charge the capacitors C 1 -CN. The current limiting element  212  also functions to limit a value of the current from the supply node  208  that is provided to the storage node so that the supply voltage VIPS or VEPS is not damaged when the capacitor bank  204  is initially being charged. Initially, before the capacitor bank  204  is charged a voltage of approximately zero volts will be present on the storage node  210 . This means that without the current limiting element  212  the supply voltage VEPS, VIPS coupled to the supply node  208  would initially be coupled directly to ground in this situation, drawing excessive amounts of current from the sources generating the supply voltages and possibly damaging these sources, as will be appreciated by those skilled in the art.  
         [0015]     The current control circuit  202  further includes a rectifying element  214  coupled between the supply node  208  and the storage node  210  to provide current from the storage node to the supply node when the supply voltage VS drops below a minimum threshold value. The rectifying element  214  also prevents the flow of current from the supply node to the storage node. In one embodiment, the current limiting element  212  is formed by a series-connected diode D 1  and a resistor R, while in another embodiment the current limiting element is formed by the resistor alone. In one embodiment the rectifying element  214  is formed by a diode D 2  having its anode coupled to the storage node  210  and cathode coupled to the supply node  208 . In other embodiments different circuitry could be utilized in place of the resistor R, diode D 1 , and diode D 2  to perform the equivalent functions, as will be appreciated by those skilled in the art.  
         [0016]     In operation of the power control circuit  200 , the SC signal is normally applied to the switching circuit  206  to close the switch SW 1  and open the switch SW 2 . As a result, the internal supply voltage VIPS is applied through the switch SW 1  as the supply voltage VS on the supply node  208 . Initially, such as when an electronic device (not shown) containing the power control circuit  200  is first turned on, the voltage on the storage node  210  and thus the voltage VCB across the capacitors C 1 -CN is zero volts. At this point, current flows through the current limiting element  212  from the supply node  208  to the storage node  210  to charge the capacitors C 1 -CN until the voltage VCB is approximately equal to the internal supply voltage VIPS. The current limiting element  212  limits the amount of current that is applied from the supply node to the storage node so that the source (not shown) of the internal supply voltage VIPS is not damaged. The time required to charge the voltage VCB to approximately the internal supply voltage VIPS is determined substantially by the value of the resistor R and the equivalent capacitance of the capacitor bank  204  (i.e., the sum of capacitors C 1  to CN). Once the capacitors C 1 -CN have been charged so that the voltage VCB approximately equals the internal supply voltage VIPS, ideally no current flows through the current limiting element  212  although in practice a small current may still flow due to leakage currents of the capacitors C 1 -CN, as will be appreciated by those skilled in the art.  
         [0017]     At this point, the power control circuit  200  maintains the state until the source of the internal supply voltage VIPS fails and the internal supply voltage drops below the desired value of the supply voltage VS. When the internal supply voltage the VIPS fails, two things occur in the circuit  200 . First, the capacitor bank  204  and rectifying element  214  operate in combination to maintain the value of the supply voltage at approximately its desired value until. More specifically, as the value of the supply voltage VS on the node  208  drops the voltage VCB across the capacitors C 1 -CN, which is initially at the desired value of the supply voltage VS, current flows from the capacitors through the rectifying element  214  to the supply node  208  to maintain the value of the supply voltage at approximately its desired value. Note that in the embodiment of  FIG. 2  where the rectifying element  214  is a diode D 2 , the value of the supply voltage VS at this point would be approximately the forward voltage drop of the diode less than the desired value of the supply voltage. No current flows through the resistor R at this point due to the reversed biased diode D 1  in the embodiment of  FIG. 2 .  
         [0018]     The second thing that occurs when the internal supply voltage VIPS fails is that control circuitry (not shown) detects this failure by detecting when the internal supply voltage falls below a minimum threshold. When the control circuitry detects this situation, the control circuitry applies the SC signals to the switching circuit  206  to open the switch SW 1  and isolate the failed source of the internal supply voltage VIPS from the supply node  208 . At the same time, the SC signals close the switch SW 2  to apply the external supply voltage VEPS to the supply node  208 . The external supply voltage VEPS thereafter supplies power to components (not shown) coupled to the power control circuit  200  to receive the supply voltage VS. Note that some charge will have been removed from the capacitor bank  204  during the period between when the failure of the internal supply voltage VIPS is first detected and when the external supply voltage VEPS is applied to the node  208 . As a result, once the external supply voltage VEPS is applied to the node  208  the capacitor bank will once again charge through the current limiting element  212 .  
         [0019]     The current control circuit  202  thus operates to perform two functions. First, the current limiting element  212  limits the current drawn from the supply voltage coupled to the supply node  208  to charge the capacitor bank  204  so that the source of the supply voltage is not damaged when the capacitor bank is initially being charged. Second, the rectifying element  202  instantaneously supplies current to the supply node  208  from the storage node  210  whenever the value of the supply voltage VS drops below a minimum threshold value. In this way, the supply voltage VS is maintained at a value sufficient to ensure proper operation of components (not shown) coupled to the circuit  200  to receive the supply voltage. The rectifying element  214  directly couples the storage node to the supply node  208  when the supply voltage VS drops below the minimum threshold value to maintain the value of the supply voltage. The rectifying element also isolates the supply node  208  from the storage node  210  during normal operation of the circuit  200  so that current to charge the capacitor bank flows only through the current limiting element  212 .  
         [0020]     In contrast to the conventional power control circuitry  102  of  FIG. 1 , the current control circuit  202  instantaneously provides current from the capacitor bank  204  to maintain the value of the supply voltage VS above the minimum threshold value until the external power supply voltage VEPS may be applied to the supply node  208 . With the current control circuit  202  there is no significant time lag between the detection of the failure of the internal supply voltage VIPS and the coupling of the capacitor bank  204  to the supply node  208 . While there is in fact some finite time lag, the dynamic manner in which the capacitor bank  204  and rectifying element  214  operate will be referred to as instantaneous herein.  
         [0021]      FIG. 3  is a functional diagram of a computer network  300  including an Ethernet switch  302  including the power control circuit  200  of  FIG. 2  according to one embodiment of the present invention. The Ethernet switch  302  receives and forwards data packets on plurality of data ports P 1 -PM to route data packets from a sending device intended receiving device in the network. Although not shown, devices are coupled to some or all of the ports P 2 -PM, and the port P 1  is coupled through an Ethernet cable  304  to a port of a second Ethernet switch  306  that operates in the same way as an Ethernet switch  302 . The Ethernet switch  306  includes additional ports  308  coupled to additional devices (not shown) in the computer network  300 . A computer system  310  is coupled to another port of the second Ethernet switch  306  that communicates through the Ethernet switches  306  and  302  two other devices in the network  300 .  
         [0022]     The network  300  further includes a power injector  312  that supplies an internal supply voltage VIPS through the Ethernet cable  304  to the power control circuit  200  in the Ethernet switch  302 . An external power supply  312  supplies an external power supply voltage VEPS to the power control circuit  200 . A data switching and control circuit  314  receives the supply voltage VS from the power control circuit  200  and includes circuitry for routing data packets between the ports P 1 -PM. The control circuit  314  further includes control circuitry for monitoring the internal supply voltage VIPS to detect a failure of the source of this voltage, and to generate the switch control signal SC to provide the external supply voltage VEPS to components in the Ethernet switch  302  when such a failure is detected. In the Ethernet switch  302 , the power control circuit  200  operates in the same way as previously described with reference to  FIG. 2  to provide the supply voltage VS to the circuit  314  and ensure proper operation of the Ethernet switch  302  even upon permanent or temporary loss of the voltage VIPS.  
         [0023]     Even though various embodiments and advantages of the present invention have been set forth in the foregoing description, the above disclosure is illustrative only, and changes may be made in detail and yet remain within the broad principles of the present invention. Moreover, the functions performed by the components illustrated in the various embodiments of the present invention can be combined to be performed by fewer elements, separated and performed by more elements, or combined into different functional blocks depending upon the particular applications of the embodiments, as will be appreciated by those skilled in the art. Therefore, the present invention is to be limited only by the appended claims.