Abstract:
Power supply apparatus, especially for the active circuits of a portable radio communication device. The power supply supplies a direct voltage to a load that is connected to a first terminal, is comprising a rechargeable battery for connection to a second terminal, and a voltage generator for recharging the battery and supplying power to the load. The power supply includes first control means for controlledly supplying current from the voltage generator to the first terminal so as to control supply of current from the voltage generator to the load and for preventing reverse flow of current from the first terminal to the voltage generator, and second control means for controlledly supplying current between the first and second terminals so as to control supply of current from the voltage generator through the first control means to the battery and from the battery to the load.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to power supply apparatus for supplying a direct voltage to a load and comprising a rechargeable battery and a voltage generator for recharging the battery and supplying power to the load,.  
       BACKGROUND OF THE INVENTION  
       [0002]     Rechargeable batteries are used in many circumstances to power user devices, especially radio communication apparatus such as portable telephones, for example. A charger comprising a voltage generator is provided to recharge the battery. The charger may take the form of an AC/DC converter or a DC/DC transformer, for example.  
         [0003]     The charger is often connectable to the user device with the battery connected so that not only can the battery be charged but the device can be used while the battery is charging. A problem arises however if the battery is completely discharged since, when the charger is connected and starts to charge the battery, the supply voltage appearing at the user device is too low for the user device to function until the battery has charged partially and remains too low for an inconveniently long time. This can be particularly troublesome in the case of a portable telephone, for example, if the delay is of the order of minutes when the user desires to make an emergency call.  
         [0004]     It is possible to provide control circuits which control the voltage and current supplied by the voltage generator and provide a parallel path for charging the battery. However these control circuits have involved a substantial additional cost.  
         [0005]     It is desirable to provide a power supply with control circuits enabling the voltage generator to power the user device even in the presence of a completely discharged battery with a smaller, or no additional cost compared to voltage supplies without such a ‘dead battery capability’.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a power supply apparatus and portable radio communication apparatus as described in the accompanying claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Error! Reference source not found. is a schematic diagram of a known power supply apparatus in a portable radio telephone,  
         [0008]     Error! Reference source not found. is a schematic diagram of a power supply apparatus in a portable radio telephone, in accordance with one embodiment of the invention, given by way of example,  
         [0009]     Error! Reference source not found. is a table showing graphic representations of control elements in the apparatus of Error! Reference source not found. in different functional states, and  
         [0010]     Error! Reference source not found. is a table showing the functional states of control elements in the apparatus of Error! Reference source not found. in different operational conditions of the apparatus, using the graphic representations of Error! Reference source not found. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]      FIG. 1  shows a portable radio communication apparatus, in this example a portable radio telephone  1 . The portable telephone  1  comprises a communication module including active signal processing, memory and audio circuits forming a load  2  energised by a power supply applying a voltage to a terminal  3  of the load. The power supply includes a rechargeable battery  4  connected to a terminal  5  for supplying power to the load  2  during normal usage of the telephone  1 .  
         [0012]     The power supply also comprises a charger  6  in the form of a voltage generator that may be connected to a terminal  7  of the telephone  1  to charge the battery  4  and, if necessary, to power the load  2 . Typically, the charger is an AC/DC converter but it may alternatively be a DC/DC transformer, for example. The charger  6  supplies power to the battery  4  along a charging path  8  to a connection point  9  connected with the battery terminal  5  through a current sensing resistor  10 . The connection point  9  is connected to the load terminal  3  through a blocking control element  11  whose function is described below. The control element and other control elements described below are operated under the control of microcontroller unit  12 .  
         [0013]     The charger terminal  7  is connected to the charging path  8  in series through a clamp control element  13  to a connection point  14 . The charging path  8  then includes in series a charge control element  15 , a reverse current blocking control element  16  and a current sense resistor  17 .  
         [0014]     The control elements are discrete field-effect transistors (‘FETs’) and, in this example are unidirectional FETs. As illustrated by the symbol of a diode, the FETs allow a parasitic current to flow even when subjected to a reverse voltage.  
         [0015]     In operation, with the charger  6  disconnected, the battery  4  supplies power through the current sensing resistor  10  and the blocking control element  11  to the terminal  3  and the load  2 , the blocking control element  11  being biased to a conducting state by the MCU  12 .  
         [0016]     When the charger  6  is connected, in normal charging conditions, the charger supplies power through the charging path  8  to the connection point  9 , the charging current being controlled by the MCU through the charge control element  15  in dependence on the voltages and currents sensed.  
         [0017]     If the charger  6  is connected to the terminal  7  before being energised and power is then applied, the voltage at the terminal  7  can be excessive. This condition is monitored by the MCU  12  and regulated through the clamp control element  13 .  
         [0018]     If the charger is unplugged (de-energised) while still connected to the terminal  7  with the battery  4  charged, the MCU  12  switches the reverse current blocking control element  16  to a non-conductive state to prevent the flow of reverse current into the charger  6 .  
         [0019]     If the battery  4  is at a low state of charge, the charger  6  is able to supply sufficient power to operate the active circuits of the load  2 . However, if the state of charge of the battery  4  is too low, the charger cannot raise the voltage at the terminal  3  to a sufficient level to operate the active circuits of the load  2  until the battery  4  has charged at least partially; this can take several minutes, during which time the telephone is unusable. Accordingly, a supply path  18  is provided in parallel with the charging path  8  to enable the charger  6  to supply power directly to the terminal  3  and the load  2 . A blocking control element  19  is connected in series in the parallel path  18  and the MCU  12  normally maintains the blocking control element  19  non-conducting and the blocking control element  11  conducting so that the power supply and charging currents from the charger  6  pass along the path  8  and are controlled by the control elements  15  to  17 . However, when the MCU  12  senses that the battery voltage is too low, it makes the blocking control element  19  conducting and the blocking control element  11  non-conducting, so that the charger  6  supplies power to the terminal  3  and the load  2  along the path  18  and the battery  4  is disconnected from the terminal  3  so as not to drag down the voltage at the terminal while the battery is still discharged.  
         [0020]     The voltage supply apparatus shown in  FIG. 1  fulfils the basic function of enabling the charger  6  to power the load  2  with a dead battery  4  or with the battery  4  removed but it requires  5  discrete control components, which adds cost to the telephone, and in addition, these components occupy space on the circuit board, which further increases the cost of ensuring dead battery operation.  
         [0021]     The voltage supply apparatus of the embodiment of the present invention is able to provide dead or missing battery operation with fewer components, comparable with the number of components in a telephone incapable of dead battery operation, so that the dead or missing battery operation feature involves substantially no on-cost.  
         [0022]     In  FIG. 2 , elements that are similar to those of  FIG. 1  bear similar reference numbers. The charger terminal  7  is connected to the connection point  9  through a charging path  8 . The load terminal  3  is connected directly to the connection point  9 . The MCU  12  controls the charging current in, and the voltage applied to the path  8  through a clamp and charge control element  20  in series in the path  8 , reverse current being controlled by the blocking element  16 . A blocking and charge control element  21  is connected in series with the current sense resistor  10  between the battery terminal  5  and the connection point  9 .  
         [0023]     The charging clamp and charge control element  20  and the battery clamp and charge control element  21  are controlled by the MCU  12  to present a high impedance, non-conductive state or a low impedance, conductive state or a controlled impedance state in which their impedance is controlled as a function of the sensed current and/or voltage variables so as to control the magnitude of the currents they supply.  
         [0024]     In operation, with the charger  6  disconnected, the battery  4  supplies power through the blocking control element  21  and the current sensing resistor  10  to the terminal  3  and the load  2 , the blocking control element  21  being biased to a conducting state by the MCU  12 .  
         [0025]     When the charger  6  is connected, in normal charging conditions, the charger supplies power through the charging path  8  to the connection point  9 , the charging current being controlled by the MCU through the charge control elements  20  and  21  in dependence on the voltages and currents sensed. The proportion of current supplied to the battery  4  instead of the load  2  is controlled by the charge control element  21 .  
         [0026]     If the charger  6  is connected to the terminal  7  before being energised and power is then applied, the voltage at the terminal  7  is regulated by the MCU  12  through the clamp control element  20 .  
         [0027]     If the charger is unplugged (de-energised) while still connected to the terminal  7  with the battery  4  charged, the MCU  12  switches the reverse current blocking control element  16  to a non-conductive state to prevent the flow of reverse current into the charger  6 .  
         [0028]     If the battery  4  is at a low state of charge, the charger  6  is able to supply sufficient power to operate the active circuits of the load  2 . However, if the state of charge of the battery  4  is too low, the blocking and charge control element  21  connected in series between the battery terminal  5  and the connection point  9  is rendered non-conducting by the MCU  12 , so that the charger  6  supplies power to the terminal  3  and the load  2  with the battery  4  disconnected from the connection point  9  so as not to drag down the voltage at the terminal if the battery is totally discharged; the battery can charge over the path  8  even while the charger  6  supplies power to the load  2  if the charger power supply is sufficient, the MCU  12  putting the blocking and charge control element  21  in an intermediate impedance state such that the voltage at the connection point  9  and the load terminal  3  is higher than the voltage at the battery terminal  5 .  
         [0029]     When the battery  4  is partially charged to a battery voltage less than full charge, the telephone can be used with power supplied from the charger  6  over the path  8  while the battery is charging. The MCU  12  puts the clamp and charge control element  20  and the blocking and charge control element  21  in the intermediate, controlled impedance state or a fully conductive state, according to the power supply conditions so that the charger  6  supplies appropriate current both to the battery and to the load.  
         [0030]     In one embodiment of the invention, when the battery  4  reaches full charge, the MCU  12  puts the clamp and charge control element  20  into its non-conductive state, so as to disconnect the charger  6  from the load  2  and the battery  4 .  
         [0031]     In another embodiment of the invention, when the battery  4  is at full charge with the charger connected, the MCU  12  puts the blocking and charge control element  21  into its non-conductive state, so as to disconnect the battery  4  from the load  2  and the charger  6 , so as to leave the battery  4  in its fully charged condition during use of the telephone.  
         [0032]     The control elements  16  and  20  are preferably FETs and preferably unidirectional FETs. However, the control element  20  may be a bidirectional FET. It is also possible for the blocking control element  16  to be a diode. The control element  21  is preferably a unidirectional FET.  
         [0033]     The operation of this embodiment of the invention will now be described in more detail with reference to  FIGS. 3 and 4  of the drawings.  FIG. 3  shows the simplified symbols used in  FIG. 4  to represent the different operational states of the control elements  16 ,  20  and  21 , as shown by their equivalent circuit diagrams in  FIG. 3 . Thus, a control element  22  in a non-conductive state is represented as a single open switch in the case of a single FET  23  or a dual open switch in the case of a dual FET  24 . A control element  25  in a fully conductive state is represented as a single closed switch in the case of a single FET  26  or a dual closed switch in the case of a dual FET  27 . A control element  28  in a voltage regulating state is represented by a voltage limiting symbol in the case of a single FET  29  or a voltage limiting symbol in series with a closed switch in the case of a dual FET  30 . A control element  31  in a current regulating state is represented by an arrow in the case of a single FET  32  or an arrow in series with a closed switch in the case of a dual FET  33 .  
         [0034]      FIG. 4  shows the operating states of the control elements  20 ,  16  and  21  for the cases of no charger connected, of a low power charger connected, capable of supplying the load while charging the battery when the load is operating in conditions of low current consumption, and of a high power charger connected, capable of supplying the load while charging the battery even when the load is operating in conditions of high current consumption. The operating states are shown for the conditions of no battery connected, of a depleted (‘dead’) battery, of a battery in low but normal uncharged condition, of a battery close to full charge, where the charger is to supply in ‘top-off conditions, and of a full battery.  
         [0035]     When no charger  6  is connected, the MCU  12  puts both the control elements  16  and  20  non-conductive and the control element  21  either non-conductive (A) if the load  2  is not being used or conductive (B) if it is.  
         [0036]     When a low- or high-power charger  6  is connected, the MCU  12  puts the charging clamp and charge control element  20  in the voltage clamp state and the blocking element  16  conductive. If there is no battery  4  connected (C), the MCU  12  puts the control element  21  non-conductive. If the battery  4  is connected (D), the MCU  12  puts the control element  21  in current-regulated state to conduct ‘trickle’ current, enabling the load  2  to operate at full voltage while still charging the battery  4 , albeit slowly.  
         [0037]     When a low-power charger  6  is connected with an at least partially charged battery  4  connected, the MCU  12  puts the control element  20  in current-regulated state, with the blocking element  16  conductive, for a normally low battery (E), the current being reduced by the control element  20  during ‘top-off’ when the battery  4  is close to full charge (G); in each case, the control element  21  is conductive so that the battery  4  can charge while the load  2  is operating under power supplied from the charger. When battery  4  is fully charged (I), the MCU  12  puts the control element  20  and the blocking element  16  non-conductive, the control element  21  being conductive so that the battery  4  supplies the load  2 .  
         [0038]     When a high-power charger  6  is connected with an at least partially charged battery  4  connected, the MCU  12  puts the control element  20  in current-regulated state, with the blocking element  16  conductive, for a normally low battery (F), the current being reduced by the control element  21  during ‘top-off’ when the battery  4  is close to full charge (H), in which case, the control element  20  is in voltage-regulation state. When battery  4  is fully charged (J), the MCU  12  puts the control element  21  non-conductive, the control element  21  being in voltage-regulation state and the blocking element  16  being conductive so that the charger  6  supplies the load  2  and preserves the charge of the battery  4 .