Power supply apparatus for efficient power conservation of a battery
BACKGROUND OF THE INVENTION 
     The present invention relates to a power supply apparatus applicable to portable equipment. 
     Of the many types of portable equipment, a portable bar code reader (handy terminal) has attracted interest. The portable equipment such as the portable bar code reader encases devices such as a CPU the and a memory. This portable bar code reader, as illustrated in FIG. 7, comprises an evenly flat type casing 91 whose tip portion is used as a reading opening 92. Light emitted from a light-emitting diode 93 advances through a condensing lens, formed in a portion of a dust protective plate 94 at the vicinity of the aforementioned opening 92, to a bar code C. The light reflected on the bar code C is incident on an image sensor 96 through a lens 95 within the casing 91 so as to be processed by a CPU (not shown) provided on a printed circuit board 97. After processing by the CPU, necessary information is displayed on a display 98. A plurality of push-buttons are provided on the casing 91, and one of the plurality of push-buttons is used as a power switch 7. The operations of the respective circuits provided in the handy terminal are ensured by a power of a battery 1 disposed within a casing 91. Generally, a Ni--Cd cell is used as the battery 1. This is because an alkaline cell, which is the most commonly used cell, has a problem in that its output voltage gradually decreases from its rated voltage (1.5 V) with use so as to make it difficult to surely keep the voltage constant. 
     However, although keeping its rated voltage (1.2 V) relatively constant, the Ni--Cd cell has a disadvantage in that the output voltage rapidly decreases when reaching the end of its lifetime, which is generally shorter than that of the alkaline cell. In addition, a special charging device is required for quickly charging the Ni--Cd cell, thus making it difficult to easily use it. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a power supply apparatus which is capable of using an alkaline cell, manganese cell or the like and adequately supplying a power concurrently with use of a handy terminal for a longer time than is usually associated with such cells. 
     This invention is based on the fact that, when not using the handy terminal, most of the current consumption occurs in a back-up of a RAM. However, the voltage necessary for the RAM back-up is as small as about 2 V (whereas the operating voltage of the the handy terminal is somewhat larger, such as about 4.8 V). 
     According to this invention, a power supply apparatus comprises boosting means for boosting a voltage from a battery to supply the boosted voltage to a memory and a back-up power source provided in parallel to the memory. A voltage to be supplied from the back-up power source to the memory is compared with a reference voltage in comparison means. Switching means provided between the battery and the boosting means is closed when a power supply switch is in a turned-on state, and closed for a predetermined time when the voltage from the back-up power source is lower than the reference voltage and the power supply switch is in a turned-off state. 
     Thus, when the power supply switch is turned on, the switching means couples the battery to the boosting means to cause the boosted voltage to be applied to the memory so that a hand-held terminal or the like effects normal operations such as a reading and writing operation. On the other hand, when the power supply switch is in the turned-off state, the switching means is intermittently turned on when the voltage from the back-up power source to the memory is lower than the reference voltage, whereby the back-up power source is charged up to the boosted voltage so as to ensure the back-up of the memory. The switching means is again turned-off after charging the back-up power source. 
     This arrangement allows the use of the hand-held terminal or the like for a relatively long time concurrently with a normal operation of the hand-held terminal or the like irrespective of the use of an easy cell such as alkaline or manganese as the battery. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The object and features of the present invention will become more readily apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a block diagram showing a basic arrangement of a power supply apparatus according to this invention; 
     FIG. 2 is a circuit diagram showing an arrangement of a power supply apparatus according to a first embodiment of this invention; 
     FIG. 3 is a circuit diagram showing an arrangement of a boosting circuit which can be used in the apparatus shown in FIG. 2; 
     FIG. 4 is a flow chart showing an operation of a CPU to be effected in the apparatus shown in FIG. 2; 
     FIG. 5 is a graphic illustration for describing the variation of a memory voltage in the apparatus shown in FIG. 1; 
     FIG. 6 is a circuit diagram showing an arrangement of a power supply apparatus according to a second embodiment of this invention; and 
     FIG. 7 is a cross-sectional view showing a conventional hand-held terminal. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram showing a basic arrangement of a power supply apparatus according to this invention. In FIG. 1, designated at numeral 3 is a boosting means 3 coupled through a switching means 2 to a battery 1 to boost the voltage of the battery 1 and then apply it to a memory 6. The switching means 2 is operated by a switching control means 8. When turning ON a power switch 7, the switching control means 8 operates the switching means 2 to cause the boosting means 3 to be coupled to the battery 1. Further, the switching control means 8 is coupled to a comparison means 5 which is in turn coupled to the boosting means 3 and a capacitor 4 disposed in parallel to the memory 6. The comparison means 5 detects the supply voltage to the memory to generate an output signal when the supply voltage thereto is lower than a reference voltage. The switching control means 8 operates the switching means 2 in accordance with the output signal of the comparison means 5 to cause the battery 1 to be coupled to the boosting means 3 for a predetermined time period when the power switch 7 is in the OFF state. 
     FIG. 2 is a circuit diagram showing a detailed arrangement of a power supply apparatus according to a first embodiment of this invention. The apparatus, together with a CPU, being provided on a printed circuit board of a hand-held terminal (see FIG. 7). In FIG. 2, a switching circuit (switching means) 2 couples the battery 1 to a boosting circuit (boosting means) 3 and comprises a main transistor 21 connected to an electric wire 11 advancing toward a RAM 6. The energization (activation) of the main transistor 21 is controlled by an auxiliary transistor 22 which is connected to the base side of the main transistor 21. The auxiliary transistor 22 is coupled through a diode 23 to another auxiliary transistor 24 which is in turn connected to the battery 1. To the base side of the auxiliary transistor 24 there is coupled a momentary type power supply switch 7 (see also FIG. 7). Here, the battery 1 comprises two alkaline cells (rated voltage of each being 1.5 V) connected in series to each other thereby forming a 3 volt rated power source. 
     The boosting circuit 3 comprises a reactor 31, a boost circuit 39, and a rectifier diode 32 which are connected to the above-mentioned electric wire 11. As shown in FIG. 3, the secondary side voltage of the rectifier diode 32 smoothed by an auxiliary capacitor 33 is fed back to a comparator 34, after being resistively potential-divided, so as to be compared with a constant voltage from a constant-voltage generator. When the divided voltage is lower than the constant voltage, the comparator 34 generates an output whereby an oscillator 35 operates so as to ON-OFF-drive a power transistor 37 through a driver 36. When the transistor 37 is in the OFF state, a high voltage is output from the secondary side of the reactor 31 and then smoothed by the auxiliary capacitor 33 to produce a predetermined high direct-current voltage (4.8 V). If the input voltage at wire 11 is in a range of 1.8 to 3.6 V, this boosting circuit 3 accurately outputs the boosted voltage of 4.8 V. 
     Returning to FIG. 2, the boosted voltage is input to a power supply terminal Vcc of a CPU 8 which also acts as the switching control means. To a PSW terminal of the CPU 8 there is input a secondary side voltage of the power supply switch 7. The operating state of the power supply switch 7 is detectable by this input voltage. The output of a PHLD terminal of the CPU 8 is coupled to the base of the auxiliary transistor 22 of the switching circuit 2. Further, the boosted voltage is supplied through a diode 82 to a main capacitor 4 connected in parallel to a memory 6. The terminal voltage (i.e., the supply voltage to the memory 6) of the capacitor 4 is detected by a comparator (comparison means) 5. The comparator 5 includes a compare circuit 59 and compares the aforementioned terminal voltage with a reference voltage (for example, 2.2 V). When the boosted voltage is lower than the reference voltage, the comparator 5 generates an output signal with a high or &#34;H&#34; level from a gate 52. This output signal is input through a diode 51 to the base of the auxiliary transistor 22 of the switching circuit 2. 
     The operation of the power supply apparatus thus arranged will be described hereinbelow with reference to FIGS. 4 and 5. The hand-held terminal is started in response to a press of the power supply switch 7. The auxiliary transistors 24 and 22 then energize whereby the main transistor 21 is energized to cause the battery voltage to be applied to the boosting circuit 3. The boosted voltage is supplied to the CPU 8 and the memory 6 in addition to charging the main capacitor 4. Thus, the CPU 8 starts by detecting the signal level of the power supply switch 7 when pressed at the PSW terminal (step 101 in FIG. 4) and, because of the high &#34;H&#34; level, performs a step 102 to set the PHLD terminal output to the high &#34;H&#34; level. At this time, even after the power supply switch 7 is released, the auxiliary transistor 22 is maintained in an energized state. In this energized state, the CPU 8 performs normal processing operations using the memory 6 in response to a reading of the bar code (step 103). To turn off the hand-held terminal, the power supply switch 7 is again pressed. Because the PSW terminal is again signaled at a high &#34;H&#34; level (step 104), the CPU 8 sets the PHLD terminal output to the &#34;L&#34; level (step 105). In response to releasing the power supply switch 7, the auxiliary transistor 22 and the main transistor 21 assume non-energizing states and the operation of the CPU 8 stops. This timing is indicated by A in FIG. 5. Since the supply of the battery voltage stops, the memory voltage (the boosted voltage of the main capacitor 4) gradually decreases from 4.8 V. When the memory voltage becomes lower than 2.2 V which is slightly higher than the back-up guarantee voltage 2 V of such memory devices (B in FIG. 5), the comparator 5 generates the output signal with the &#34;H&#34; level whereby the auxiliary transistor 22 and the main transistor 21 take the energizing states so that the supply of the boosted voltage again causes to cause the CPU 8 to operate. 
     Since the signal level of the PSW terminal is at a low &#34;L&#34; level, the operation advances from the step 101 to a step 106 in FIG. 4 so as to set the PHLD terminal output to the high &#34;H&#34; level to supply the battery voltage for 5 seconds (steps 107 and 108). Accordingly, the memory voltage again increases up to 4.8 V. Thereafter, whenever the memory voltage becomes lower than 2.2 V, the battery voltage is supplied to start the CPU 8 and raise the memory supply voltage. 
     Thus, even while the voltage of the battery 1 using alkaline cells gradually decreases over time and use from 3 V to 1.8 V, an adequate operating voltage is still supplied from the boosting circuit 3 to the CPU 8 and the memory 6, and the discharge of the battery 1 is only intermittently effected at the time of the back-up and therefore minimizes the consumption thereof. This allows for a long-time use of the hand-held terminal irrespective of the use of easy cells such as alkaline or manganese. 
     A description will be made hereinbelow in terms of a second embodiment of this invention. According to the above-described first embodiment, if the cells of the battery 1 are taken out for exchange at the time that the memory voltage decreases to within the vicinity of around 2.2 V, the output signal of the comparator 5 maintains a high &#34;H&#34; level as it is, whereby there is the possibility that the discharge will occur rapidly in the main capacitor 4 and hence the voltage will become lower than the back-up guarantee voltage (2 V). The second embodiment eliminates this problem and is arranged such that a one-shot circuit 53 is provided in the passage from the comparator 5 to the auxiliary transistor 22 and at the output side of the gate 52 as shown in FIG. 6. The output signal with a relatively large current value to operate the auxiliary transistor 22 is generated only for a predetermined time (for example 1 second) and hence the discharge of the capacitor 4 is prevented so as to maintain the back-up guarantee voltage. 
     It should be understood that the foregoing relates to only preferred embodiments of the present invention, and that it is intended to cover all changes and modifications of the embodiments of the invention herein used for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention. For example, although in the above-described embodiment the momentary type switch is used as the power supply switch 7, it is also appropriate to use an alternate type switch therefor.