Patent Publication Number: US-2013241500-A1

Title: Charge control circuit

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to charge control circuits, and particularly, to a charge control circuit applied to charging a battery. 
     2. Description of Related Art 
     In order to prevent a battery from being damaged during charging, the charge temperature of the battery is limited to a temperature range, typically 0° C.-45° C. The battery should not be charged if the temperature of the battery is out of the temperature range. In order to detect the temperature of the battery, a thermistor whose resistance value varies with temperature of the battery is employed. The change of resistance of the thermistor causes the voltage of the thermistor to change accordingly. An integrated chip can detect the corresponding voltage of the thermistor to determine whether the temperature of the battery is out of the temperature range. However, the integrated chip is not dedicated to the function, and integrates so many functions that the temperature of the battery may not be detected accurately enough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure should be better understood with reference to the following drawings. The units in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding portions throughout the several views. 
         FIG. 1  is a block diagram of a charge control circuit in accordance with an exemplary embodiment. 
         FIG. 2  is a circuit diagram of the charge control circuit of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described with reference to the drawings. 
     Referring to  FIG. 1 , a charge control circuit  100  is used to stop charging a battery  200  if the temperature of the battery  200  is out of the charge temperature range of the battery  200 . In this embodiment, the charge temperature range is 0-45° C. The charge control circuit  100  includes a resistance module  10 , a voltage comparing module  20 , and a charge control module  30 . The charge control module  30  is electrically connected to the battery  200 . 
     The resistance module  10  includes a power supply Vcc, a first resistor R 1 , and a thermistor R 2  whose resistance varies with the temperature of the battery being charged. In this embodiment, the resistance value of the thermistor R 2  decreases with any increase of the temperature of the battery  200 . The first resistor R 1  and the thermistor R 2  are serially connected between the power supply Vcc and the ground. A connection node N 1  is formed between the first resistor R 1  and the thermistor R 2 . In this embodiment, the power supply Vcc is configured to provide an external voltage to the circuit  100 . 
     The voltage comparing module  20  includes a voltage comparing chip  21 , a third resistor R 3 , a forth resistor R 4 , a fifth resistor R 5 , a sixth resistor R 6 , a seventh resistor R 7 , a first transistor Q 1 , and a second transistor Q 2 . The voltage comparing chip  21  includes a first input pin IN 1 , a second input pin IN 2 , a third input pin IN 3 , a forth input pin IN 4 , a first output pin OUT 1 , and a second output pin OUT 2 . The second input pin IN  2  and the third input pin IN 3  are both connected to the first connection node N 1 . The input voltage of the second input pin IN 2  and the third input pin IN 3  are both equal to the voltage of the thermistor R 2 . The third resistor R 3  and the forth resistor R 4  are serially connected between the power supply Vcc and the ground, and a second connection node N 2  is formed between the third resistor R 3  and the forth resistor R 4 . The second connection node N 2  is connected to the first input pin IN 1 , and the input voltage of the first input pin IN 1  is equal to the voltage of the forth resistor R 4 . The fifth resistor R 5  and the sixth resistor R 6  are serially connected between the power supply Vcc and ground, and a third connection node N 3  is formed between the fifth resistor R 5  and the sixth resistor R 6 . The third connection node N 3  is connected to the forth input pin IN 4 , and the input voltage of the forth input pin IN 4  is equal to the voltage of the sixth resistor R 6 . The first output pin OUT 1  is connected to the base terminal of the first transistor Q 1 , and the second output pin OUT 2  is connected to the base terminal of the second transistor Q 2 . The emitter terminals of the first transistor Q 1  and the second transistor Q 2  are connected to the power supply Vcc via the seventh resistor R 7 . The collector terminals of the first transistor Q 1  and the second transistor Q 2  are connected to ground. The emitter terminal of the first transistor Q 1  and the second transistor Q 2  are also connected to an input pin THM of the charge control module  30 . 
     In this embodiment, if the temperature of the battery  200  changes, the resistance of the thermistor R 2  changes accordingly. The change of the resistance of the thermistor R 2  causes a corresponding change in the input voltage at the second input pin IN 2  and the third input pin IN 3 . 
     In this embodiment, the second connection node N 2  provides an upper limit voltage to the first input pin IN 1 , and the upper limit voltage can be adjusted by adjusting the resistance value of the resistors R 3  and R 4 . In this embodiment, the upper limit voltage corresponds to a minimum temperature within the charge temperature range 0-45° C. The charge control circuit  100  stops charging the battery  200  if the temperature of the battery  200  is less than the minimum temperature of the allowed range. The third connection node N 3  provides a lower limit voltage to the forth input pin IN 4 , and the lower limit voltage can be adjusted by adjusting the resistance value of the resistors R 5  and R 6 . The lower limit voltage corresponds to the maximum of the allowed charge temperature range. The charge control circuit  100  stops charging the battery  200  if the temperature of the battery  200  is equal to or more than the maximum temperature of the allowed range. 
     The voltage comparing chip  21  compares the input voltage of the second input pin IN 2 , which is equal to the voltage of the thermistor R 2 , with the upper limit voltage of the first input pin IN 1 , and compares the input voltage of the third input pin IN 3  with the lower limit voltage of the forth input pin IN 4 , and can determine whether or not the voltage of the thermistor R 2  is between the upper and lower voltage limits, and thus to determine whether the temperature of the battery  200  is within the charge temperature range. 
     If the voltage comparing chip  21  determines that the voltage of the thermistor R 2  is equal to or greater than the upper limit, that is to say, the temperature of the battery  200  is lower than the allowed limit, the voltage comparing chip  21  controls the first output pin OUT 1  to output a low-level voltage to the first transistor Q 1 , and the first transistor Q 1  is thus conductive. In this embodiment, the actual voltage value of the low-level voltage may be 0V. Simultaneously, the comparing chip  21  controls the second output pin OUT 2  to output a high-level voltage to the second transistor Q 2 , and the second transistor Q 2  is cut off. In this embodiment, the actual voltage value of the high-level voltage may be 1V. The input pin THM of the charge control module  30  receives a first voltage as a control signal from ground via the conductive transistor Q 1 . In this embodiment, the voltage value of the first voltage received from the ground is 0V. The charge control module  30  stops charging the battery according to the control signal. In this embodiment, the charge control module  30  takes the first voltage as the control signal to stop charging the battery  20 . 
     If the voltage of the thermistor R 2  is determined to be lower than the allowed lower limit, the voltage comparing chip  21  controls the first output pin OUT 1  to output a high-level voltage to the first transistor Q 1 , and the first transistor Q 1  is cut off. Simultaneously, the comparing chip  21  controls the second out put pin OUT 2  to output a low-level voltage to the second transistor Q 2  to conduct the second transistor Q 2 . The input pin THM of the charge control module  30  receives the first voltage as a control signal from ground via the conductive transistor Q 2 . The charge control module  30  stops charging the battery according to the control signal. 
     If the voltage at the thermistor R 2  is between the upper and lower limits of the allowed voltage range, that is to say, the temperature of the battery  200  is within the charge temperature range, the voltage comparing chip  21  controls the first output pin OUT 1  and the second output pin OUT 2  to both output a high-level voltage, and the two transistors Q 1  and Q 2  are both cut off. The input pin THM of the charge control module  30  receives a second voltage from the power supply Vcc via the seventh resistor R 7 . The charge control module  30  continues to charge the battery  200 . In this embodiment, the voltage comparing chip  21  is an LM358 chip. 
     In an alternative embodiment, the voltage comparing module  20  is an intelligent chip which stores the upper and lower voltage limits. The intelligent chip includes an input/output interface (not shown) to obtain the voltage of the thermistor R 2 . The intelligent chip compares the voltage of the thermistor R 2  with the upper and lower voltage limits to determine whether the temperature of the battery  200  is in the charge temperature range. If the intelligent chip determines that the voltage of the thermistor R 2  is outside of the charge temperature range, the intelligent chip outputs a control signal from the input/output interface to the charge control module  30 . The charge control module  30  stops charging the battery  20  according to the control signal. In this embodiment, the control signal may be a pulse signal. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being exemplary embodiments of the present disclosure.