Abstract:
A battery overheating protection circuit includes a thermal resistor samples the temperature of the battery and converts the temperature into a temperature voltage, a comparison circuit compares the temperature voltage with a reference voltage for judging whether the temperature of the battery is higher than the maximum reference temperatures temperature or not. If yes, the comparison circuit outputs a protection signal to drive a charging module to stop charging the battery in the charging process, and to cut off the conducting path to draw power from the battery in the discharging process. The present invention sets two different maximum reference temperatures during charging process and discharging process by a reference voltage module, which makes the maximum allowable discharging temperature is higher than the maximum allowable charging temperature.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to battery circuits, and particularly to a battery circuit with the function of overheating protection. 
     2. General Background 
     Nowadays, handheld devices (e.g., mobile phones, media players) are more and more popular. These handheld devices are typically powered with a battery pack, which includes one or more cells to form a battery. Generally, the battery would be damaged and becomes dangerous when the temperature of the battery is too high. The temperature of the battery should be controlled below a limited temperature when the battery is either charged or discharged. 
     A circuit in related art can protect the battery from overheating when the battery is either charged or discharged. When the temperature of the battery goes higher than a predetermined temperature, the circuit interrupts charging or discharging of the battery. The circuit has the same interruption temperature for both the battery charging process and the discharging process. However, generally, charging of batteries must be halted at a certain temperature and discharging of batteries (i.e., in normal uses) must be halted at a somewhat higher temperature. In addition, the circuit adopts an intelligent chip to achieve the function of protecting the batteries from overheating, which adds to the cost. 
     According to this, it is necessary to provide a device to overcomes the above-identified deficiencies. 
     SUMMARY 
     The present invention provides an battery overheating protection circuit which can protect the battery from overheating in battery charging process and discharging process with a low cost. 
     An battery overheating protection circuit is provided, the protection circuit includes a connection jack, a charging module, a temperature detection module, a reference voltage module, a comparison circuit, a control module and a path switch. The connection jack is configured for connecting with a power source. The charging module is connected with the connection jack and is configured for recharging a battery. The temperature detection module is configured for detecting a temperature of the battery and generating a temperature voltage proportional to the temperature. The reference voltage module is configured for providing a first reference voltage in a battery charging process and a second reference voltage in a drawing battery power process. The comparison circuit is configured for comparing the temperature voltage with the first reference voltage in the battery charging process and comparing the temperature voltage with the second reference voltage in the drawing battery power process, and outputting a protection signal when the comparison result indicates the temperature of the battery goes higher than a corresponding temperature limit. The control module is configured for receiving the protection signal and disabling the charging module to charge the battery. And the path switch is located along a conducting path to draw power from the battery and configured for cutting off the conducting path when receiving the protection signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present overheating protection circuit. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a block diagram of a battery overheating protection circuit in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a circuit diagram showing a first implementation of the circuit of  FIG. 1 . 
         FIG. 3  is a circuit diagram showing a second implementation of the circuit of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to  FIG. 1 . The battery overheating protection circuit  1  includes a charging module  10 , a control module  30 , a temperature detection module  40 , a comparison circuit  50 , a reference voltage module  60 , a connection jack  80 , and a path switch  90 . 
     The charging module  10  is capable of recharging a battery  20 , the battery  20  is a rechargeable battery, and the connection jack  80  is capable of connecting to a power source. The temperature detection module  40  is used to detect a temperature of the battery  20  and generate a voltage (hereinafter, temperature voltage) proportional to the temperature. The reference voltage module  60  provides a first reference voltage V ref1  when the charging module  10  is charging the rechargeable battery  20 , and a second reference voltage V ref2  when a consuming module  100  is drawing power from the rechargeable battery  20 . The consuming module  100  includes many function components which implement one or more functions. The first reference voltage V ref1  and the second reference voltage V ref2  are predetermined values that indicate the critical temperature voltages proportional to the maximum allowable temperatures, configured for a battery charging process and a drawing battery power process respectively. The maximum allowable temperature configured for the drawing battery power process is generally higher than that for the battery charging process. The path switch  90  is located along a conducting path to draw power from the battery  20  to the consuming module  100 . The comparison circuit  50  is used to compare a current temperature voltage against the first reference voltage during the battery charging process and to compare the temperature voltage with the second reference voltage during the drawing battery power process. 
     When the connection jack  80  is connected to a power source and starts charging the battery  20 , the comparison circuit  50  compares the temperature voltage with the first reference voltage V ref1 . When the temperature voltage of the battery  20  rises above the first reference voltage V ref1 , the comparison circuit  50  outputs a protection signal to the control module  30 . When the control module  30  receives the protection signal and controls the charging module  10  to stop charging the battery  20  accordingly. The comparison circuit  50  also outputs the protection signal to an alarm module  70 . The alarm module  70  outputs an alarm signal accordingly and the alarm signal can be an audible alarm, a visual alarm, etc. 
     When power is drawn from the battery  20 , the comparison circuit  50  compares the temperature voltage with the second reference voltage V ref2 . When the temperature voltage rises above the second reference voltage V ref2 , the comparison circuit  50  outputs the protection signal to disable the path switch  90 . As a result, the consuming module  100  is no longer able to draw power from the battery  20 . Meanwhile, the comparison circuit  50  outputs the protection signal to the alarm module  70 . The alarm module  70  accordingly outputs an alarm signal. 
     Referring also to  FIG. 2 , in a first implementation, the power source is an AC/DC adaptor which capable of converting an alternating current to a direct current, and in other implementations, the power source can be a universal series bus (USB) power source (e.g., a USB port of a computer). The charging module  10  includes a control pin  101 , an input pin  102 , and an output pin  103 . The input pin  102  is connected to an anode of the connection jack  80 , the output pin  103  is connected to an anode of the battery  20 , and the control pin  101  is connected to the control module  30 . The charging module  10  is disabled when the control pin  101  is at a low voltage level. 
     The temperature detection module  40  includes a thermal resistor R 9  and a resistor R 5  which are serially connected between a positive potential node H and ground. The thermal resistor R 9  is located inside the battery  20 . In the first implementation, the thermal resistor R 9  is a negative temperature coefficient (NTC) thermal resistor having resistance that decreases with increasing temperature. The comparison circuit  50  includes an inverting input port A, a non-inverting input port B, and an output port (not shown). A connection node of the resistors R 9  and R 5  is connected to the inverting input port A of the comparison circuit  50 . 
     The control module  30  is a high voltage activated switch, while the path switch  90  is a low voltage activated switch. The control module  30  and the path switch  90  both include a control terminal, a first path terminal, and a second path terminal. In the first implementation, an n-channel metal-oxide-semiconductor field-effect transistor (NMOSFET) Q 3  and a p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET) Q 4  are taken as an example to illustrate the control module  30  and the path switch  90  respectively. Gates, sources, drains of the MOSFETs Q 3 , Q 4  constitute the control terminals, the first path terminals, the second path terminals of the control module  30  and the path switch  90  respectively. In other implementations, the control module  30  can be a negative-positive-negative (NPN) bipolar junction transistor (BJT) and the path switch  90  can be a positive-negative-positive (PNP) BJT. 
     The gates of the NMOSEET Q 3  and the PMOSFET Q 4  are both connected to the output port of the comparison circuit  50 . The NMOSEFT Q 3  and a resistor R 10  are connected in parallel between the control pin  101  of the charging module  10  and the ground. The source and drain of the NMOSFET Q 3  are connected to the ground and the control pin  101  respectively. The source of the PMOSFET Q 4  is connected to the anode of the battery  20  and the drain of the PMOSFET Q 4  is connected to the consuming module  100 . 
     The reference voltage module  60  includes a first switch  601 , a second switch  602 , a voltage-dividing circuit  603 , and a plurality of resistors R 1 , R 2 , R 3 , R 4 . The first switch  601  and the second switch  602  both include a control terminal, a first path terminal and a second path terminal. In the first implementation, the first switch  601  is an NMOSFET Q 1  and the second switch  602  is a PMOSFET Q 2 . The voltage-dividing circuit  603  includes resistors R 6 , R 7 , R 8  which are serially connected between the positive potential point H and the ground. The second switch  602  is connected in parallel with the resistor R 6 . A connection node of the resistors R 7 , R 8  is connected to the non-inverting input port B of the comparison circuit  50 , and the connection node of the resistors R 7 , R 8  provides the reference voltages V ref1  or V ref2  to the non-inverting input port B of the comparison circuit  50 . 
     To more clearly describe the first implementation, a gate of the NMOSEET Q 1  is symbolically expressed as a node C and a drain of the NMOSFET Q 1  is symbolically expressed as a node D. The node C is connected to the anode of the connection jack  80  through the resistor R 1 . The node C is further connected to the ground through the resistor R 2 . The node D is connected to the positive potential point H through the resistor R 3 . The node D is further connected to the gate of the PMOSFET Q 2 . The source of the PMOSFET Q 2  is connected to the positive potential point H, and the drain of the PMOSFET Q 2  is connected to a connection node of the resistors R 6  and R 7 . The source of the NMOSFET Q 1  is grounded. The positive potential point H provides a voltage V 1 . The voltage V 1  is drawn from the battery  20  during the drawing battery power process and from the AC/DC adaptor during the battery charging process. 
     When the AC/DC adapter is plugged into the connection jack  80  and starts charging the battery  20 . The node C, i.e., the gate of the NMOSFET Q 1  obtains a high voltage level from the connection jack  80  and switches on the NMOSFET Q 1 . The gate of the PMOSFET Q 2  is grounded through the NMOSFET Q 1  and accordingly enables the PMOSFET Q 2 . The resistor R 6  is bypassed by the PMOSFET Q 2  and the reference voltage V ref1  provided to the non-inverting port B of the comparison circuit  50  is equals to V 1 *R 8 /(R 8 +R 7 ). 
     The thermal resistor R 9  provides the temperature voltage to the inverting port A of the comparison circuit  50 . Initially, the temperature voltage is higher than the reference voltage V ref1 . The temperature voltage declines as the temperature of the thermal resistor R 9  increases gradually. When the temperature voltage drops below the reference voltage V ref1 , the comparison circuit  50  outputs the protection signal both to the NMOSFET Q 3  and the alarm module  70 . The protection signal is a high voltage level signal which enables the NMOSFET Q 3 . The control pin  101  of the charging module  10  becomes grounded through the NMOSFET Q 3 , and as a result the charging module  10  stops charging the battery  20 . In the first implementation, the alarm module  70  is activated by a high voltage level and accordingly output an alarm signal. 
     When the AC/DC adaptor is not plugged in the connection jack  80  and the consuming module  100  is drawing power from the battery  20 , i.e., the battery  20  supplies power to the consuming module  100 , the node C is maintained at a low voltage level that disables the NMOSFET Q 1 . The gate of the PMOSFET Q 2  is connected to the positive potential point H through the resistors R 3 , R 4  and obtains a high voltage level that disables the PMOSFET Q 2 . The reference voltage V ref2  is supplied to the non-inverting port B of the comparison circuit  50 . The reference voltage V ref2  is equal to V 1 *R 8 /(R 8 +R 7 +R 6 ) and lower than the reference voltage V ref1  corresponding the battery charging process. Initially, the temperature voltage is higher than the reference voltage V ref2 . The temperature voltage drops gradually while the temperature of the thermal resistor R 9  increases gradually. When the temperature voltage drops below the reference voltage V ref2 , the comparison circuit  50  outputs the high voltage level protection signal to the alarm module  70  and the PMOSFET Q 4 . As a result, the PMOSFET Q 4  is disabled and cut off the conducting path to draw power from the battery  20 . Meanwhile, the alarm module  70  receives the high voltage level protection signal and outputs an alarm signal. 
     In the first implementation, by providing the relatively higher reference voltage V ref1  during the battery charging process and the relatively lower reference voltage V ref2  during the drawing battery power process, the discharging process of the battery is halted at a somewhat higher temperature than in the charging process. 
     Referring to  FIG. 3 , in a second implementation, the second switch  602  is a high voltage activated switch such as an NMOSFET Q 5 . The thermal resistor R 9 ′ is a positive temperature coefficient (PTC) thermal resistor having resistance that increases with increasing temperature. The path switch  90  is a high voltage activated switch, an NMOSFET Q 7  which is taken as an example to illustrate the path switch  90 . The control module  30  is a low voltage activated switch and an NMOSFET Q 6 , taken as an example to illustrate the control module  30 . In the initial state, the temperature voltage is lower than the reference voltage V ref1  during the battery charging process and the reference voltage V ref2  during the drawing battery power process. 
     When the AC/DC adapter is plugged into the connection jack  80  and starts charging the battery  20 , the first switch  601  is enabled and connects the gate of the NMOSFET Q 5  to the ground. The NMOSFET Q 5  is accordingly disabled. As a result, the reference voltage V ref1  is equal to V 1 *R 8 /(R 8 +R 7 +R 6 ). The temperature voltage increases gradually as the temperature of the thermal resistor R 9 ′ increases gradually. When the temperature voltage goes above the reference voltage V ref1 , the comparison circuit  50  outputs a protection signal both to the PMOSFET Q 6  and the alarm module  70 . The protection signal is a low voltage level signal which enables the PMOSFET Q 6 . The control pin  101  of the charging module  10  is grounded through the PMOSFET Q 6 , and as a result, the charging module  10  stops charging the battery  20 . The alarm module  70  in the second implementation is activated by a low voltage level and accordingly outputs an alarm signal. 
     When the AC/DC adaptor is not plugged in the connection jack  80  and the consuming module  100  is drawing power from the battery  20 , i.e., the battery  20  supplies power to the consuming module  100 . The first switch  601  is disabled. The gate of the NMOSFET Q 5  is connected to the positive potential point H through the resistor R 3 , R 4  and obtains a high voltage level that enables the NMOSFET Q 5 , the resistor R 6  is bypassed by the NMOSFET Q 5 . The reference voltage V ref2  is equal to V 1 *R 8 /(R 8 +R 7 ) and higher than the reference voltage V ref1  configured for the battery charging process. The temperature voltage increases gradually as the temperature of the thermal resistor R 9  increases gradually. When the temperature voltage goes above the reference voltage V ref2 , the comparison circuit  50  outputs the low voltage level protection signal and transmits the protection signal to the NMOSFET Q 7  and the alarm module  70 , so that the NMOSFET Q 7  is disabled and the alarm module  70  is activated. The conducting path to draw power from the battery  20  is accordingly cut off and the alarm module  70  outputs an alarm signal. 
     In the second implementation, by providing the relatively lower reference voltage V ref1  in the charging process and the relatively higher reference voltage V ref2  in the drawing battery power process, the drawing battery power process of the battery is halted at a somewhat higher temperature than in the charging battery power process. 
     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 invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.