Abstract:
A device or a method for supplying a current to a load. A peripheral temperature of the load is detected. Based on the detected peripheral temperature and a predetermined time period, the unit amount of the current being supplied is switched between a first current and a second current.

Description:
FIELD OF THE INVENTION 
     The following disclosure relates generally to a device and a method for controlling a current, which is used to charge a load. 
     DESCRIPTION OF THE RELATED ART 
     When charging a load, such as a battery or a cell, with a charging device, the temperature around the load or the charging device, i.e., the peripheral temperature, usually increases. To control the peripheral temperature, various devices or methods for controlling a current supply have been applied, for example, as described in Japanese Patent Application Publication No. H07-222370 or H11-103405. 
     In one example, a temperature detector, which monitors the peripheral temperature, may be provided with the charging device. When the peripheral temperature reaches above a first reference peripheral temperature, the charging device reduces the unit amount of current being supplied to the battery. While this may decrease the peripheral temperature, the charging time may become longer. 
     To reduce the charging time, the charging device may increase the unit amount of current when the peripheral temperature decreases and reaches below a second reference peripheral temperature, which is set lower than the first reference peripheral temperature. While this may reduce the charging time, the unit amount of current supply may frequently change, thus increasing the level of noise, such as the high frequency harmonic noise. 
     BRIEF SUMMARY OF THE INVENTION 
     Example embodiments of the present invention provide a device or a method for supplying a current to a load. In one example, a peripheral temperature of the load is detected. Based on the detected peripheral temperature and a predetermined time period, the unit amount of the current being supplied is switched between a first current and a second current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating an example circuit configuration of a charging device according to an example embodiment of the present invention; 
         FIG. 2  is a timing chart illustrating an example operation performed by the charging device shown in  FIG. 1 ; 
         FIG. 3  is a schematic diagram illustrating an example circuit configuration of a temperature detector circuit shown in  FIG. 1 ; 
         FIG. 4  is a graph illustrating the relationship between a detected peripheral temperature and a base-to-emitter voltage, obtainable from the temperature detector circuit shown in  FIG. 1 ; and 
         FIG. 5  is a graph illustrating the relationship among a detected peripheral temperature, a base-to-emitter voltage, a detection signal value, and a detection signal voltage, obtainable from the temperature detector circuit shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In describing the example embodiments illustrated in the drawings, specific terminology is employed for clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views,  FIG. 1  illustrates a charging device  1  according to an example embodiment of the present invention. 
     Referring to  FIG. 1 , the charging device  1  supplies a current to a battery  7 , which is connected to the charging device  1 . In this example, the battery  7  is implemented by a secondary battery. The charging device  1  includes a temperature detector circuit  2 , a controller circuit  3 , and a current supply circuit  4 . 
     The temperature detector circuit  2  detects a temperature of the charging device  1 , and compares the detected temperature T with a first reference temperature T 1  or a second reference temperature T 2 . In this example, the first reference temperature T 1  is set higher than the second reference temperature T 2 . The difference between the first reference temperature T 1  and the second reference temperature T 2  may be set to be less than 5 degrees C., for example. When the detected temperature T is equal to or higher than the first reference temperature T 1 , the temperature detector circuit  2  outputs a detection signal To having the high value. When the detected temperature T is less than the second reference temperature T 2 , the temperature detector circuit  2  outputs a detection signal To having the low value. 
     The controller circuit  3  includes a pulse generator circuit  11 , a NAND circuit NA 1 , and a charge controller circuit  12 . 
     When the detection signal To having the high value is output from the temperature detector circuit  2 , the pulse generator circuit  11  generates and outputs a pulse signal Do having the high value for a predetermined time period td. Thus, the pulse signal Do has the pulse width determined by the predetermined time period td. After the predetermined time period td passes, the pulse generator circuit  11  changes the value of the pulse signal Do from the high value to the low value. 
     The NAND circuit NA 1  outputs a switch signal Co having the value determined by the values of the pulse signal Do and the detection signal To. When the values of the detection signal To and the pulse signal Do are both low, the NAND circuit NA 1  outputs the switch signal Co having the high value. When the value of at least one of the detection signal To and the pulse signal Do is high, the NAND circuit NA 1  outputs the switch signal Co having the low value. 
     The charge controller circuit  12  detects a voltage applied to the battery  7 , and compares the detected voltage with a reference voltage to output a control signal Sc. When the detected voltage is lower than the reference voltage, the charge controller circuit  12  outputs the control signal Sc having a first value, which causes the current supply circuit  4  to charge the battery  7  with a controlled current. When the detected voltage exceeds the reference voltage, the charge controller circuit  12  outputs the control signal Sc having a second value, which causes the current supply circuit  4  to charge the battery  7  with a controlled voltage. 
     The current supply circuit  4  supplies a current ic to the battery  7 . In this example, when the control signal Sc having the first value is output, the current supply circuit  4  outputs the current ic having a value determined by the value of the switch signal Co. When the switch signal Co having the high value is output, the current supply circuit  4  outputs a first current ic 1 . When the switch signal Co having the low level is output, the current supply circuit  4  outputs a second current ic 2 , which has the value smaller than the value of the first current ic 1 . For example, the value of the second current c 2  may be set to about 10% of the value of the first current ic 1 . Further, in this example, when the control signal Sc having the second value is output, the value of the current is not changed. 
     Still referring to  FIG. 1 , the current supply circuit  4  includes a soft starter circuit  15 , which causes the current supply circuit  4  to gradually switch the current between the first current ic 1  and the second current ic 2 . 
     Referring to  FIG. 2 , an example operation of the charging device  1  is explained. In this example, the charging device  1  is integrated in a single intergraded circuit chip together with the battery  7  and a transistor device. The temperature of the chip is used as the detected temperature T. 
     As the charging device  1  supplies a current to the battery  7 , the temperature of the chip, i.e., the detected temperature T, increases. When the detected temperature T reaches the first reference temperature T 1  at a timing A, the detection signal To output from the temperature detector circuit  2  is switched from the low value to the high value. At the timing A, the pulse generator circuit  11  outputs the high-value pulse signal Do, which has the pulse width of td. Since the values of the pulse signal Do and the detection signal To become high at the timing A, the switch signal Co output from the NAND circuit NA 1  is switched from the high value to the low value. 
     When the switch signal Co having the low value is output, the current supply circuit  4  supplies the second current ic 2  to the battery  7 . Since the second current ic 2  is smaller than the first current ic 1 , the detected temperature T of the chip gradually decreases after the timing A. When the detected temperature T of the chip reaches below the second reference temperature T 2  at a timing B, the temperature detector circuit  2  changes the detection signal To from the high value to the low value. In this example, a time period between the timing A and the timing B is greater than the time period td. 
     When the values of the pulse signal Do and the detection signal To become low at the timing B, the switch signal Co output from the NAND circuit NA 1  is switched from the low value to the high value. The current supply circuit  4  supplies the first current ic 1  to the battery  7 . In this example, the soft starter circuit  15  starts operating when the current is switched from the second current ic 2  to the first current ic 1 . As shown in  FIG. 2 , with the soft starter circuit  15 , the current value gradually increases such that it takes a time period ts to completely switch from the second current ic 2  to the first current ic 1 . In this manner, generation of high harmonic noise may be suppressed. 
     As the first current ic 1  is supplied, the detected temperature T of the chip starts increasing again. When the detected temperature T reaches the first reference temperature T 1  at a timing C, the detection signal To is switched from the high value to the low value. The pulse signal Do is switched from the high value to the low value. The switch signal Co is switched from the high value to the low value. 
     When the detected temperature T of the chip further decreases and reaches below the second reference temperature T 2  at a timing D, the detection signal To is switched from the high value to the low value. At the timing D, the pulse signal Do is not switched from the high value to the low value, since the time period td is not passed. As shown in  FIG. 2 , the time period between the timing C and the timing D is less than the time period td. Since the switch signal Co retains the low value, the current supply circuit  4  continues to supply the second current c 2  to the battery  7 . When the timing period td passes at a timing E, the pulse signal Do is switched from the high value to the low value as the values of the detection signal To and the pulse signal Do become low at the timing E. Accordingly, the current is gradually switched from the second current ic 2  to the first current ic 1 . As described above referring to  FIG. 1  or  2 , the control circuit  3  prevents the current supply circuit  4  from switching the current for the predetermined time period td after the current has been changed. In this manner, generation of high frequency noise may be suppressed. 
     Referring to  FIG. 3 , an example circuit configuration of the temperature detector circuit  2  is explained. The temperature detector circuit  2  includes an operational amplifier AMP 1 , a comparator CMP 2 , a supply voltage generator circuit  21 , a reference voltage generator circuit  22 , a PNP transistor Q 1 , and a resistor R 1 . 
     The operational amplifier AMP 1  has a non-inverse input terminal connected to the supply voltage generator circuit  21 , and an inverse input terminal connected to its output terminal. The output terminal of the operational amplifier AMP 1  receives a supply voltage Vs, which is generated by the supply voltage generator  21 . The output terminal of the operational amplifier AMP 1  is further connected to an emitter of the PNP transistor Q 1  via the resistor R 1 . The PNP transistor Q has a base and a collector, each of which is connected to the ground. The operational amplifier AMP 1  supplies a current to the PNP transistor Q 1  via the resistor R 1 . The base-to-emitter voltage of the PNP transistor Q 1 , i.e., the base-to-emitter voltage Vbe, increases or decreases proportionally relative to the detected temperature T of the chip. For example, as shown in  FIG. 4 , as the detected temperature T increases, the base-to-emitter voltage Vbe decreases. 
     The comparator CMP 2  has a non-inverse input terminal connected to the reference voltage generator Vr, and an inverse input terminal connected to the emitter of the PNP transistor Q 1 . The comparator CMP 2  compares the base-to-emitter voltage Vbe with a reference voltage Vr generated by the reference voltage generator Vr, and outputs the detection signal To. 
     In this example, the comparator CMP 2  may be implemented so as to have hysteresis characteristics, which may be observed when using a Schmitt trigger. In this example, as shown in  FIG. 4  or  5 , the hysteresis width of the comparator CMP 2  is set to be substantially equal to the difference between a first reference voltage Vbe 1  and a second reference voltage Vbe 2 . The first reference voltage Vbe 1  is the voltage Vbe obtained when the detected temperature T reaches the first reference temperature T 1 . The second reference voltage Vbe 2  is the voltage Vbe obtained when the detected temperature T reaches the second reference temperature T 2 . 
     For example, when the detected voltage Vbe is below the first reference voltage Vbe 1 , the comparator CMP 2  outputs the detection signal To having the low value. When the detected voltage Vbe is above the second reference voltage Vbe 2 , the comparator CMP 2  outputs the detection signal To having the high value. When the detected voltage Vbe is between the first reference voltage Vbe 1  and the second reference voltage Vbe 2 , the value of the detection signal To is not changed. In this manner, the function of the temperature detector circuit  2  may be performed with the relatively simple structure. 
     Referring to  FIG. 5 , when the temperature T of the chip increases and reaches the second reference temperature T 2 , the detection signal To or the voltage Vto of the detection signal To retains the low value. When the temperature T continues to increase and reaches the first reference temperature T 1 , the detection signal To or the voltage Vto of the detection signal To is switched from the low value to the high value. 
     When the temperature T of the chip decreases and reaches the first reference temperature T 1 , the detection signal To or the voltage Vto of the detection signal To retains the high value. When the temperature T continues to decrease and reaches the second reference temperature T 2 , the detection signal To or the voltage Vto of the detection signal is switched from the high value to the low value. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specifications may be practiced in ways other than those specifically described herein. 
     For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     In another example, the charging device  1  may be implemented in various other ways. For example, the NAND circuit NA 1  may be substituted by an AND circuit and an inverter circuit, or any other kind of switching circuit. The pulse generator  11  may be substituted by any other kind of timing circuit capable of counting the time period td. The soft starter circuit  15  may not be provided in the charging device  1 . The soft starter circuit  15  may cause the current supply circuit  4  to gradually decrease the current from the first current ic 1  to the second current ic 2 . 
     Further, a charging device, such as the charging device of  FIG. 1 , may be integrated into a single integrated circuit chip together with a battery and/or any kind of circuit, including, for example, a drive circuit. The chip may be incorporated into any kind of apparatus, such as an image forming apparatus, a communication apparatus, automobile, information processing apparatus, image processing apparatus, etc. 
     This patent application is based on and claims priority to Japanese patent application No. 2005-196330 filed on Jul. 5, 2005, in the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.