Patent Document

CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application is a continuation of U.S. patent application Ser. No. 12/574,209, filed Oct. 6, 2009 now U.S. Pat. No. 7,777,454 and entitled BATTERY CHARGER WITH TEMPERATURE CONTROL, which is a continuation of U.S. patent application Ser. No. 11/636,337, filed Dec. 8, 2006 now U.S. Pat. No. 7,598,710 and entitled BATTERY CHARGER WITH TEMPERATURE CONTROL, both of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to the field of electronic circuits. More particularly, the present invention relates to battery charger integrated circuit. 
     BACKGROUND 
     It is a common experience that when charging a battery, the battery charger integrated circuit (IC) that generates the charging current tends to overheat. The rise in temperature is caused by the IC power consumption in form of heat dissipation of the charging current. Naturally, when the charging current is reduced, the heat is also reduced. Over the years, there have been many attempts to achieve an optimal charging current value that effectively charges the battery and does not overheat battery charger IC at the same time. Some of these attempts seem to be either too complicated or too expensive. Because most of the rechargeable batteries are used in consumer electronic products, the cost and the size of the battery charger IC are important factors for the electronics manufacturers. 
     The present invention provides an effective, small-sized, and inexpensive circuit and a method to achieve both effective charging and overheating prevention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  illustrates a block diagram of a battery charger with temperature control that has a temperature sensing circuit and a charging current generator circuit in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates a detailed schematic diagram of the battery charger with temperature control in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a flow chart illustrating a method of temperature control in a batter charger circuit in accordance with an embodiment of the present invention 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to different embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these different embodiments, it will be understood that they are not intend to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of the ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention. 
     Now referring to  FIG. 1 , a block diagram of a battery charger integrated circuit (IC) with temperature control  100  in accordance with an embodiment of the present invention is illustrated. Battery charger integrated circuit with temperature control  100  includes a temperature sensing circuit  100  electrically coupled to a charging current generator circuit  120 . Temperature sensing circuit  110  receives a first reference voltage (VREF 1 )  101  and reading temperature voltage (VDT) obtained from a direct temperature measurement of battery charger integrated circuit  100 . In one embodiment, a die temperature indicator (DTI)  102  is used to measure the temperature of battery charger integrated circuit  100 . The current generated by the die temperature indicator (DTI)  102  is proportional to the temperature of battery charger integrated circuit  100 . This current is converted into temperature reading voltage (VDT) by a sensing resistor (RT)  103 . Temperature sensing circuit  110  compares the temperature reading voltage (VDT) with the first reference voltage (VREF 1 ) and generates a second reference voltage (VREF). The second reference voltage (VREF) is, in turn, fed to charging current generator circuit  120 . Charging current generator circuit  120  uses the second reference voltage (VREF) to generate a reference current (I 1 ) and a charging current (IOUT) for a battery  160  that is plugged into battery charger integrated circuit  100 . In one embodiment, charging current (IOUT) mirrors the reference current (I 1 ) and is linearly proportional to second reference voltage (VREF), e.g., IOUT is proportional to VREF. 
     In operation, temperature sensing circuit  110  compares the temperature reading voltage (VDT) with first reference voltage (VREF 1 ). Whenever temperature reading voltage (VDT) surpasses first reference voltage (VREF 1 ), temperature sensing circuit  110  adjusts second reference voltage (VREF). As such, charging current generator circuit  120  senses the adjustment in second reference voltage (VREF) and changes the reference current (I 1 ) that, in turn, changes the charging current (IOUT). In one embodiment, temperature sensing circuit  110  is constructed so that second reference voltage (VREF) is linearly proportional to first reference voltage (VREF 1 ) and temperature reading voltage (VDT). In one embodiment, temperature sensing circuit  110  is constructed in such a manner that second reference voltage is a function of the first reference voltage (VREF 1 ) and the temperature reading voltage (VDT). It is noted that any relationship between first reference voltage (VREF 1 ) and second reference voltage (VREF) so that the change in the temperature reading voltage (VDT) causes a change in second reference voltage (VREF) that causes a change in the charging current (IOUT) is within the scope of the present invention 
     Now referring to  FIG. 2 , the detailed schematic diagram of a battery charger integrated circuit with temperature control  200  in accordance with an embodiment of the present invention is illustrated. More particularly, temperature sensing circuit  110  includes a first error amplifier  201  that is electrically coupled to a first n-channel Metal Oxide Semiconductor (nMOS)  202  and a resistive divider circuit configured by a first resistor (R 1 )  203  and a second resistor (R 2 )  204 . More particularly, first reference voltage (VREF 1 ) is electrically connected to an inverting terminal of first error amplifier  201 . Die temperature indicator (DTI)  102  is connected between the inverting terminal and non-inverting terminal of first error amplifier  201 . Sensing resistor (RT) is connected to the non-inverting terminal of first error amplifier  201  and an electrical ground  111 . The output terminal of first error amplifier  201  is electrically coupled to the gate of first nMOS transistor  202 . First resistor (R 1 )  203  is electrically connected to the inverting terminal of first error amplifier  201  and the drain of first nMOS transistor  202 . Second resistor (R 2 )  204  is electrically coupled between the drain and the source of first nMOS transistor  202 . 
     Continuing with  FIG. 2 , charging current generator circuit  120  includes a second error amplifier  211  connected in series to a second nMOS transistor  212 , and current mirror circuit configured by a first pnp bipolar junction transistor  214  and a second pnp bipolar junction transistor  215 . More particularly, first pnp bipolar junction transistor  215  and second pnp bipolar junction transistor  215  form a current mirror with first pnp bipolar junction transistor  214 . First pnp bipolar junction transistor  214  is connected as a diode and its collector connected to the drain of second nMOS transistor  212 . The collector of second pnp bipolar junction transistor  215  is connected to battery  162 . The bases of first pnp bipolar junction transistor  214  and second bipolar junction transistor are connected together and to an input voltage (VIN)  150 . The non-inverting terminal of second error amplifier  211  is connected to the source of second nMOS transistor  212  and to a resistor (RC)  213 . The other terminal of resistor (RC)  213  is connected to electrical ground  111 . 
     Referring again to  FIG. 2 , in operation, when reading temperature voltage (VDT) is less than first reference voltage (VREF 1 ), the output of first error amplifier  201  is LOW, causing first nMOS transistor  202  to be in cutoff mode. As a result, second reference voltage (VREF) equals to first reference voltage (VREF 1 ) divided by the sum of first resistor (R 1 )  203  and second resistor (R 2 )  204  and multiplied by second resistor (R 2 )  204 . However, as the temperature of battery charger integrated circuit  200  increases, temperature reading voltage (VDT) also increases. If temperature reading voltage (VDT) exceeds first reference voltage (VREF 1 ), the ratio between first reference voltage (VREF 1 ) and second voltage reference (VREF) will start to change. Second reference voltage (VREF) is fed to charging current generator circuit  120 . There, second reference voltage (VREF) is compared with voltage (VX) at the non-inverting terminal of second error amplifier  211 . Second error amplifier  211  is configured such that it sets voltage (VX) equals to second reference voltage (VREF). Thus, the reference current (I 1 ) equals second reference voltage (VREF) divided by resistor (RC)  213 . In one embodiment, first npn bipolar transistor (Q 1 ) and second npn bipolar transistor (Q 2 )  215  have different sizes so that the charging current (IOUT) is proportional to the reference current (I 1 ) by a factor of K. When the temperature reading voltage (VDT) exceeds first reference voltage (VREF 1 ), reflecting the limit in the temperature of the die temperature indicator (DTI)  102  is reached, first error amplifier  201  adjusts its output voltage that turns on first nMOS transistor  202 . The turning on of first nMOS transistor  202  changes the value of resistive divider ratio by bypassing currents to electrical ground  111  from second reference voltage (VREF) node, thus changing second reference voltage (VREF). This change in second reference voltage (VREF) is introduced to charging current generator circuit  120  at the non-inverting terminal of second error amplifier  211 . The lowering of second reference voltage (VREF) reduces the gate voltage of second nMOS transistor  212 . Thus, the reference current (I 1 ) is also reduced. As a consequence, the charging current (IOUT) will also be reduced. 
     Now referring to  FIG. 3 , a flow chart  300  representing a method of providing temperature control for a battery charger circuit is illustrated. Method  300  includes the steps of providing a temperature reading voltage, providing reference voltages that are related to the temperature reading voltage, comparing the first reference voltage (VREF 1 ) with the temperature reading voltage (VDT), and adjusting the second reference voltage (VREF) in order to reduce the temperature whenever the temperature reading voltage (VDT) surpasses the first reference voltage (VREF 1 ). 
     Now referring to step  301 , a temperature reading voltage (VDT) is provided that is proportional to the die temperature indicator of the batter charger circuit. In reality, step  301  is implemented by connecting a die temperature indicator (DTI) to a sensing resistor (RT) across the two input terminals of an error amplifier such as first error amplifier  201  as shown in  FIG. 2  of the present invention. 
     Referring now to step  302 , a first reference voltage (VREF 1 ) is provided. Also in step  302 , a second reference voltage (VREF) is derived from first reference voltage (VREF 1 ). Then, a reference current (I 1 ) and charging current (IOUT) are generated using the second reference voltage (VREF). Step  302  is implemented by connecting first reference voltage (VREF 1 ) source to the inverting terminal of first error amplifier  201  as shown in  FIG. 1  and  FIG. 2 . 
     Referring to step  302 , temperature reading voltage (VDT) is compared with first reference voltage (VREF 1 ). Step  302  is implemented by first error amplifier  201  connected to die temperature indicator (DTI)  102  and sensing resistor (RT)  103  as shown in  FIG. 2  of the present invention. 
     Referring now to step  304 , whenever the temperature reading voltage (VDT) surpasses the first reference voltage (VREF 1 ), adjusting the second reference voltage (VREF) so that the charging current (IOUT) is adjusted. Step  304  is implemented by temperature sensing circuit  110  connected to charging current generator circuit  120  as shown in  FIG. 2 . If the temperature reading voltage (VDT) is less than the first reference voltage, continue step  303  and the normal operation of battery charger circuit  200 . 
     Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. It should be understood, of course, the foregoing disclosure relates only to a preferred embodiment (or embodiments) of the invention and that numerous modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims. Various modifications are contemplated and they obviously will be resorted to by those skilled in the art without departing from the spirit and the scope of the invention as hereinafter defined by the appended claims as only a preferred embodiment(s) thereof has been disclosed.

Technology Category: 4