Patent Publication Number: US-2017373529-A1

Title: Battery backup arrangement

Description:
FIELD OF THE INVENTION 
     The invention relates to a battery backup arrangement in a power supply. 
     BACKGROUND OF THE INVENTION 
     Typically, an alternating current (AC) mains supply voltage is coupled via a two or three input terminal connector that is accessible from outside an enclosure containing an electronic device, for example, a gateway set-top box. The AC voltage energizes the gateway set-top box except when power interruption occurs. 
     Some users require a battery backup operation feature for energizing at least a selected portion of the circuitry when an interruption in the mains supply voltage is detected. Consequently, a selected portion of the typical functions performed by the gateway set-top box continues to be performed after the mains supply voltage interruption occurs. 
     In order to produce a versatile gateway set-top box and also reduce the cost for those users who do not require the battery backup operation feature, it may be desirable not to include a battery and at least some of its associated circuitry in the enclosure containing the gateway set-top box. Thus, for those users who do not require the battery backup operation feature, a power cord connected to the AC mains supply voltage source applies the AC voltage via the aforementioned input terminal connector. On the other hand, for those users who do require the battery backup operation feature, it may be desirable to provide the battery and its associated circuitry as an add-on, separate unit that is installed outside and separate from the enclosure containing the gateway set-top box. 
     In a preferred embodiment, the separate add-on unit applies, via a power cord connected to the previously mentioned input connector, an unfiltered rectified AC voltage having a direct current DC component, as long as no power interruption occurs. The unfiltered rectified AC voltage has a waveform of, for example, a full wave rectified sine wave. On the other hand, when power interruption occurs, an output of the battery is coupled to a boost converter for producing a filtered DC voltage at a sufficiently large magnitude, for example, approximately 140 volts DC. The filtered DC voltage is applied via the aforementioned gateway power input connector using a power cord that interfaces with the aforementioned gateway power input connector for energizing a conventional internal AC-to-DC power supply converter of the gateway set-top box. In this way, the same type of gateway set-top box unit can be used by a user who requires the battery backup operation feature and a user who does not require the battery backup operation feature. Advantageously, those users who do not require the battery backup operation feature need not include the separate add-on unit with the gateway set-top box and, consequently, enjoy the associated benefit of cost reduction. 
     In carrying out another advantageous feature, a detector contained in the gateway set-top box enclosure detects whether the boosted filtered DC voltage is applied to the connector that is indicative of power interruption. When the boosted filtered DC voltage is detected in the detector of the gateway set-top box, it produces an output signal that is used for disabling current consumption in a portion of the circuitry of the gateway set-top box in a manner to reduce the rate of battery discharge. On the other hand, when an unfiltered waveform is detected, either rectified or unrectified, that is indicative of normal uninterrupted power, the entire circuitry of the gateway set-top box is powered. 
     SUMMARY 
     In an advantageous embodiment, an add-on power supply module provides battery backup capability for an electronic apparatus. It includes a backup battery for developing a backup battery voltage and a passive rectifier for rectifying an alternating current (AC), mains supply voltage to develop an unfiltered rectified output supply voltage at an output connector of the power supply module that is adaptable to be selectively connected to an input connector of the electronic apparatus to energize a power supply regulator of the electronic apparatus. The unfiltered rectified output supply voltage charges the backup battery, when the AC mains supply voltage is available. A first sensor detects when the AC mains supply voltage is unavailable. A boost converter is responsive to an output of the first sensor for developing said filtered direct current (DC) boosted supply voltage at the output connector from the backup battery voltage, in substitution for the unfiltered rectified output supply voltage, when the AC mains supply voltage is unavailable. 
     In another advantageous embodiment, an electronic apparatus includes a power supply regulator and a passive rectifier for rectifying an alternating current (AC), mains supply voltage to energize the power supply regulator, when the AC mains supply voltage is selectively developed at an input connector. The passive rectifier applies an input, unfiltered rectified input supply voltage to energize the power supply regulator, when the unfiltered rectified mains supply voltage is selectively developed at the input connector and applies a filtered direct current (DC) boosted supply voltage that is indicative of battery backup operation to energize the power supply regulator, when the filtered DC boosted supply voltage is selectively developed at the input connector. A sensor responsive to the voltage developed at the input connector senses when the filtered DC boosted supply voltage is selectively developed at the input connector. A switch responsive to an output of the first sensor reduces current loading at the input connector, when sensor is indicative of the filtered DC boosted supply voltage being developed at the input connector, but not when any of the AC mains supply voltage and the unfiltered rectified input supply voltage is sensed by the sensor. The current reduction is implemented by turning off unessential function in the set top box. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates in a partial block diagram a battery backup unit, embodying an advantageous feature; and 
         FIG. 2  illustrates in a block diagram a gateway set top box, embodying an additional advantageous feature, which is energized by the battery backup unit of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates, partially in a block diagram, an add-on battery backup unit  200 , embodying an advantageous feature. A source, not shown, of an alternating current (AC) mains voltage ACin is coupled to a conventional full-wave bridge rectifier  201 . Rectifier  201  includes a diode D 4  having an anode coupled to a common conductor G and a cathode coupled to an input terminal  201   a . A diode D 1  has an anode that is coupled to a second input terminal  201   b  and a cathode coupled to an output terminal  201   c  of bridge rectifier  201 . Mains voltage ACin is applied between terminals  201   a  and  201   b  when terminals  201   a  and  201   b  are coupled to, for example, a conventional electric wall plug, not shown. Diodes D 4  and D 1  rectify a positive half wave, not shown, of voltage ACin to produce a half-wave portion VOUTa of a full wave rectified unfiltered output voltage VOUT, when voltage ACin is uninterrupted. Similarly, full-wave bridge rectifier  201  includes a diode D 2  having an anode coupled to common conductor G and a cathode coupled to terminal  201   b . A diode D 3  has an anode that is coupled to terminal  201   a  and a cathode coupled to output terminal  201   c  of bridge rectifier  201 . Diodes D 2  and D 3  rectify a negative half wave, not shown, of voltage ACin to produce a half-wave portion VOUTb of full wave rectified unfiltered output voltage VOUT, when voltage ACin is uninterrupted. Voltage VOUT is applied to an output terminal  205   a  of a connector  205  of add-on battery backup unit  200 . An output terminal  205   b  of connector  205  is coupled to ground potential G. 
     In add-on battery backup unit  200 , voltage VOUT is, additionally, coupled via a diode D 5  and a filter capacitor C 2  to a conventional battery charging circuit  202 , not shown in details, for energizing battery charging circuit  202  when voltage ACin is uninterrupted. Diode D 5  prevents capacitor C 2  from filtering voltage VOUT at terminal  205   a . Battery charging circuit  202  is coupled to a backup battery  203 , for example, of the Lithium-ion (Li-ion) type that produces a battery voltage V 2  for energizing a boost converter  204 , when an interruption occurs in mains voltage ACin. 
     Except as noted, boost converter  204  is of a conventional design in that it is energized from lower DC voltage V 2  of battery  203  that can be in a voltage range, for example, between 8V and 12V. Boost converter  204  produces, during the power interruption, a filtered constant DC level voltage VOUT 1  that excludes significant AC voltage component or ripple. Voltage VOUT 1  is developed at terminal  205   a  at, for example, 140V that is approximately close to the peak voltage of voltage VOUT, prior to an interruption. Thus, voltage VOUT 1  is produced in substitution of voltage VOUT that is no longer produced, or could have been produced at a magnitude below a normal operation threshold level, as a result of an interruption referred to as brownout in mains voltage ACin. 
     A metal oxide field effect transistor (MOSFET) switch M 1  is pulse-width modulated by a conventional boost control circuit  206  to store regulated amounts of energy in a boost inductor L 1 . Inductor L 1  is coupled between a terminal  203   a  of battery  203  and a first main current conducting terminal Mia of MOSFET switch M 1 . Main current conducting terminal Mia of MOSFET switch M 1  is coupled to an anode of a rectifier diode D 6  having a cathode that is coupled to a filter capacitor C 1  for reducing any significant AC component in voltage VOUT 1 . 
     A junction terminal  207 , coupled between the cathode of diode D 6  and capacitor C 1 , is coupled to an anode of an isolating/coupling diode D 7  having a cathode that is coupled to terminal  205   a  for developing filtered DC voltage VOUT 1 , when power interruption occurs. On the other hand, when power interruption does not occur, diode D 7  isolates terminal  205   a  from capacitor C 1  to prevent AC voltage from feeding back into boost converter  204  and, in particular, to prevent capacitor C 1  from filtering voltage VOUT. Preventing the filtering of voltage VOUT is desirable for implementing an advantageous AC voltage interruption detection, as described later on. 
     An output signal  206   a  of boost control circuit  206  is coupled to a gate terminal of MOSFET switch M 1  to control its duty cycle. Should voltage VOUT 1  tend to decrease, a duty cycle of output signal  206   a  would tend to increase, resulting in a longer MOSFET switch M 1  conduction time. Consequently, output voltage VOUT 1  tends to increase. For that purpose, terminal  207  applies in a conventional manner a regulating negative feedback signal to a control input  206   b  of boost control circuit  206 . As a result, the output voltage at terminal  207  is regulated to be constant in the face of varying load current conditions. 
     MOSFET switch M 1  has a second main current conducting terminal that is coupled to a current sensing resistor R 1 . A junction terminal between resistor R 1  and MOSFET switch M 1  is coupled to a terminal  206   c  of boost control circuit  206  to provide in a conventional manner over-current protection for MOSFET switch M 1 . 
     Battery voltage V 2  is also coupled to energize a conventional AC power detection circuit  208 . AC power detection circuit  208  is responsive to a voltage VSENSE developed at terminal  201   a  for detecting whether AC voltage ACin is within a normal operation range or is interrupted. When AC voltage ACin is present, for example, after being restored, AC power detection circuit  208  produces, in response to voltage VSENSE, a control signal  208   a  that is coupled to boost control circuit  206  for disabling MOSFET switch M 1  via boost control circuit  206 . Consequently, generation of voltage VOUT 1  is disabled. Instead, generation of voltage VOUT at terminal  205   a  is restored. On the other hand, when interruption in AC voltage ACin is detected, control signal  208   a  enables boost control circuit  206  to activate MOSFET switch M 1  for producing voltage VOUT 1 . 
       FIG. 2  illustrates a block diagram of a router or gateway set-top box  100 , embodying an advantageous feature, for providing internet and phone service at, for example, a user home. Similar symbols and numerals in  FIGS. 1  an  2  indicate similar items or functions. 
     A controller  101  of  FIG. 2  is coupled via conductors  104  to a 4-Port Ethernet switch  102  for providing Ethernet connection at the user home. 4-Port Ethernet switch  102  is conventional. Similarly, controller  101  is coupled via conductors  107  to a subscriber line interface card (SLIC)  108  for providing telephone service. SLIC  108  is also conventional. 
     In a system configuration in which add-on battery backup unit  200  of  FIG. 1  is not utilized, a power cord, not shown, applies AC mains voltage ACin having no DC component via a connector  305  of  FIG. 2  that mates with an input voltage connector  105  for rectifying voltage ACin in a conventional front end bridge rectifier  110   a  formed by a four diode, not shown in details, of an AC-to-DC converter  110 . On the other hand, in a system configuration in which add-on battery backup unit  200  of  FIG. 1  is utilized, a power cord, not shown, electrically connects connector  205  to input voltage connector  105  of  FIG. 2  via a connector  405  that mates with connector  105 . Thereby, voltage VOUT of  FIG. 1  is applied to bridge rectifier  110   a  in AC-to-DC converter  110 , when voltage ACin is available. Similarly, voltage VOUT 1  of  FIG. 1  is applied to bridge rectifier  110   a  in AC-to-DC converter  110 , when voltage ACin is unavailable. 
     Bridge rectifier  110   a  of AC-to-DC converter  110  is constructed similarly to bridge rectifier  201  of  FIG. 1 . Bridge rectifier  110   a  of  FIG. 2  produces an output voltage  110   c  that is applied to a conventional voltage regulator  110   b . Voltage regulator  110   b  produces in a conventional manner, not shown in details, a filtered DC voltage Vdc at an output of AC-to-DC converter  110 . Voltage Vdc is coupled to a conventional voltage regulator  111  that produces supply voltages collectively referred to as voltages Vsupply for energizing gateway set top box  100  including controllers  101 , switch  102  and SLIC  108 . 
     As explained before, when filtered constant DC voltage VOUT 1  is generated at connector  205  of  FIG. 1  and at connector  105  of  FIG. 2 , it does not contain a significant AC component. The absence of any significant AC component is indicative of power interruption. On the other hand, when unfiltered full wave rectified voltage VOUT of  FIGS. 1 and 2  is generated, a significant AC component is generated so that voltage VOUT developed in connector  105  of  FIG. 2  is indicative that no power interruption has occurred. 
     In carrying out an advantageous feature, a power-fail detector  114  senses the voltage, voltage VOUT or VOUT 1 , developed in connector  105 . A power-fail detecting output signal  114   a  produced at an output of power-fail detector  114  is indicative whether voltage ACin of  FIG. 1  has been interrupted. Output signal  114   a  of  FIG. 2  is coupled to an input terminal  101   a  of controller  101 . 
     Detector  114  may be implemented, in a conventional manner, not shown, by AC-coupling the voltage developed in connector  105  of  FIG. 2  and then rectifying the AC-coupled voltage. When voltage VOUT of  FIG. 1  is applied, a significant rectified AC-coupled voltage will be detected for producing power-fail detecting signal  114   a  of  FIG. 2  at, for example, a so-called HIGH level at the output of power-fail detector  114  that is indicative of uninterrupted voltage ACin of  FIG. 1 . 
     As explained before, voltage VOUT 1  is filtered in capacitor C 1  in a manner to exclude significant AC components for enabling power interruption detection in power fail detector  114  of  FIG. 2 . When voltage VOUT 1  is applied, no rectified AC-coupled voltage will be detected in detector  114 . Therefore, power-fail detecting signal  114   a  of  FIG. 2  will be generated at a so-called LOW level that is indicative of interrupted voltage ACin of  FIG. 1 . 
     It may be desirable to reduce the total current loading from the battery  203  of  FIG. 1  in order to lengthen the battery remaining time, during battery backup operation. Thus, in response to signal  114   a  of power fail detector  114 , controller  101  of  FIG. 2  initiates, in an otherwise conventional manner, a shutdown procedure or operation of selected functions/devices such as of switch  102 . By shutting-down current consumption in switch  102 , a reduction of a load current  118  is obtained. Thereby, current consumption from battery  203  of  FIG. 1  is, advantageously, reduced. On the other hand, advantageously, controller  101  maintains SLIC  108  operational because it is required to remain active for continuing to provide phone service, during battery backup operation.