Abstract:
A thermal protection circuit for high output power supplies. A power supply circuit includes a switching control circuit coupled to a switching regulator circuit. The switching control circuit is configured to generate a plurality of switching control signals for controlling the switching regulator circuit. The power supply circuit also includes a temperature sensitive circuit which includes a thermistor. The temperature sensitive circuit is configured to provide a variable voltage level output to the phase control circuit. The switching control circuit is also configured to suspend operation of the switching regulator circuit upon detecting a predetermined voltage level at the output.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to power supplies and, more particularly, to the protection of microprocessor power supplies. 
     2. Description of the Related Art 
     Power supplies are used in various types of devices. There are many specialized types of power supply circuits with various advantages and disadvantages. Microprocessors in computers may require a power supply circuit that regulates a high level of current while maintaining a high level of efficiency. 
     One such type of specialized power supply circuit is a switching regulator. Switching regulator circuits typically provide a lower voltage output than the unregulated input while at the same time providing a higher current than the current drawn from the unregulated supply. This is accomplished using a transistor that is constantly switching between a saturation mode and a non-conducting mode. Typically a transistor that is optimized for power applications, such as a power field effect transistor, is used. Because the transistor is either in saturation or not conducting, there is very low power dissipation. A switching regulator therefore can regulate a high amount of current at a high efficiency rate. 
     Since these power supply circuits regulate a high level of current during normal operation, they may also generate a significant amount of heat while operating. Under normal operating conditions the heat may not cause problems. However, under less than ideal conditions such as, for example, short circuits, improper power supply operation and unacceptable environmental conditions, the heat may become excessive. Excessive heat may cause damage to various computer system components including the motherboard, the microprocessor, or the power supply itself. 
     The heat generated by the switching regulator may be controlled by methods such as directed airflow and the use of heat sinks. These methods may be effective in some cases, but in order to accommodate the worst case operating conditions, those methods may be expensive. Additionally, it may be impossible to anticipate the worst possible conditions. 
     SUMMARY OF THE INVENTION 
     Various embodiments of a power supply circuit including a thermal protection circuit are disclosed. In one embodiment, the power supply circuit includes a switching control circuit coupled to a switching regulator circuit. The switching control circuit is configured to generate a plurality of switching control signals for controlling the switching regulator circuit. The power supply circuit also includes a temperature sensitive circuit including a thermistor. The temperature sensitive circuit is configured to provide a variable voltage level output to the phase control circuit. The switching control circuit is also configured to suspend operation of the switching regulator circuit upon detecting a predetermined voltage level at the output. 
     In another embodiment, the power supply circuit includes a phase control circuit coupled to a first switching regulator circuit and to a second switching regulator circuit. The phase control circuit is configured to generate a plurality of switching control signals for controlling switching of the first and second switching regulator circuits. The phase control circuit is also configured to selectively suspend operation of the second switching regulator circuit in response to receiving a signal indicative of a low power mode of operation. The power supply circuit also includes a temperature sensitive circuit which includes a thermistor. The temperature sensitive circuit is configured to provide a variable voltage level output to the phase control circuit. The phase control circuit is further configured to suspend operation of the first and second switching regulator circuits upon detecting a predetermined voltage level at the output. 
     In various other embodiments, the thermistor is configured to detect an elevation in temperature of the first switching regulator circuit or the second switching regulator circuit and to change a resistance value internal to the thermistor. Furthermore, the thermistor is configured to decrease the internal resistance value in response to detecting the elevation in temperature. The temperature sensitive circuit develops the predetermined voltage level in response to the thermistor decreasing the internal resistance value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block of one embodiment of a switching power supply circuit. 
     FIG. 2 is a block diagram of one embodiment of a multiphase switching power supply circuit. 
     FIG. 3 is a diagram of one embodiment of a motherboard of a computer system including a power supply circuit. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1, a block diagram of one embodiment of a switching power supply circuit is shown. The switching power supply circuit of FIG. 1 includes a switching control circuit  60  coupled to a switching regulator circuit  70 . The output of switching regulator circuit  70  is Vout  80  and it may used to power a microprocessor (not shown). Switching control circuit  60  is also coupled to a temperature sensitive circuit  10 . 
     In this embodiment, switching regulator circuit  70  may include one or more power transistors and various other components (not shown), which are used to regulate a supply voltage for use by a microprocessor or other device. It is noted that in other embodiments there may be more switching regulator circuits. Switching control circuit  60  is configured to generate control signals for switching regulator circuit  70 . The control signals switch the transistors on and off. 
     In one embodiment, switching control circuit  60  includes an enable input, which when activated by an active enable signal  50  allows normal operation of switching control circuit  60 . However, when enable signal  50  is deactivated, switching control circuit  60  suspends operation of switching regulator circuit  70 . In this embodiment, an active signal means a logic value of one, while a deactivated signal refers to a logic value of zero. 
     A node  40  of temperature sensitive circuit  10  is connected to the enable input of switching control circuit  60 . In one embodiment, temperature sensitive circuit  10  is a voltage divider circuit, which includes a thermistor  20  and a resistor  30 . One lead of resistor  30  is connected to VCC, while the other lead of resistor  30  is connected to one lead of thermistor  20 . The second lead of thermistor  20  is connected to circuit ground. The voltage divider circuit develops a voltage across resistor  30  and thermistor  20  proportional to the resistance of each component. Therefore, to calculate the voltage at node  40  of FIG. 1, the equation is as follows: V node =VCC (R thermistor )/(R thermistor +R resistor ). However, since the resistance value of thermistor  20  varies with changes in temperature, the voltage developed at node  40  also varies with changes in temperature. In this particular embodiment, the resistance value of thermistor  20  decreases with increases in temperature. This type of thermistor is said to have a negative temperature coefficient. It is contemplated that other types of thermistors may be used, such as those having a positive temperature coefficient. In other embodiments, it is contemplated that other temperature sensitive circuits may be used such as, for example, active components such as transistors. Additionally, if the enable input of switching control circuit  60  were an active low input, the voltage divider may be reconfigured such that thermistor  20  is connected to VCC and resistor  30  is connected to ground. 
     As described above, the voltage developed at node  40  is dependent upon the selected resistance value of resistor  30  and the ambient resistance value of thermistor  20 . If the ambient temperature of thermistor  20  increases, the resulting decrease in the resistance value of thermistor  20  will cause a proportional decrease in the voltage at node  40 . Conversely, a decrease in the ambient temperature of thermistor  20  will cause an increase in the voltage at node  218 . The voltage at node  40  may vary between zero volts and the maximum voltage level capable of developing across thermistor  20  depending on the selected resistance value of resistor  30  and the range of resistance values that thermistor  20  can achieve. Therefore, to achieve a particular ambient temperature voltage level at node  40 , proper resistance values must be calculated and chosen for resistor  30  and thermistor  20 . 
     As will be described in more detail below, thermistor  20  is located such that it may detect a rise in a temperature corresponding to the ambient operating temperature of switching regulator circuit  70 . If the ambient temperature begins to increase, the resistance value of thermistor  20  will begin to decrease causing a proportional decrease of the voltage at node  40 . If the voltage decreases below the threshold of the enable input circuitry of switching control circuit  60 , then switching control circuit  60  will detect the enable signal  50  as inactive and switching control circuit  60  will disable operation of switching regulator circuit  70 . This action will power down any devices that are powered by switching regulator circuit  70 . 
     If the ambient temperature begins to decrease, the resistance value of thermistor  20  will begin to increase causing a proportional increase of the voltage at node  40 . If the voltage increases above the threshold of the enable input circuitry of switching control circuit  60 , then switching control circuit  60  will detect the enable signal  50  as active and switching control circuit  60  will enable operation of switching regulator circuit  70 . This action will power up any devices that are powered by switching regulator circuit  70 . 
     Referring to FIG. 2, a block diagram of one embodiment of a multiphase switching power supply circuit is illustrated. Components that are identical to those shown in FIG. 1 are numbered identically for simplicity and clarity. The multiphase switching power supply circuit of FIG. 2 includes four switching regulator circuits  110 A-D coupled to a phase control circuit  150 . The output of each of switching regulator circuits  110 A-D is coupled together at node Vout  170 . Phase control circuit  150  is also coupled to a temperature sensitive circuit  10 . 
     In this particular embodiment, power supply circuit  100  comprises synchronous switching regulator circuits designated as  110 A,  110 B,  110 C and  110 D. Synchronous switching regulator circuits  110 A-D may, individually or collectively be referred to as switching regulator circuit  110  or switching regulator circuits  110 , respectively. Switching regulator circuits  110  are coupled to provide power to microprocessor  160  at Vout  170 . It is important to note that different embodiments may comprise more or less than four switching regulator circuits. 
     In the illustrated embodiment, each switching regulator  110  includes a pair of transistors (e.g., transistors  101  and  102 , transistors  111  and  112 , etc.) coupled between a power supply terminal VCC and ground. Each switching regulator  110  further includes a diode (e.g., diodes  103 ,  113 , etc.), an inductor (e.g. inductors  104 ,  114 , etc.) and a capacitor (e.g., capacitors  105 ,  115 , etc.). It is noted that other specific circuit arrangements may be employed to implement each switching regulator  110 . 
     Phase control circuit  150  is configured to generate a plurality of control signals for controlling the states of the transistors in switching regulators  110  such that the switching regulators  110  operate out of phase with respect to one another. In a particular embodiment, phase control circuit  150  may include a Semtech SC 1144  integrated circuit. As will be described in further detail below, phase control circuit  150  also includes circuitry to selectively suspend operation of a subset of switching regulators  110  during a low power mode of operation to thereby allow for improved efficiency. Phase control circuit  150  also includes further circuitry to suspend operation of all of switching regulator circuits  110 . 
     Phase control circuit  150  activates (i.e. turns on) transistors  101 , 111 , 121  and  131 , respectively, during different phases of operation. During a first phase of operation (“phase 1”), transistor  101  is turned on while transistors  111 ,  121  and  131  are turned off. Since each switching regulator  110  is embodied as a synchronous regulator, when transistor  101  is turned on, transistor  102  is turned off (in response to a corresponding control signal from phase control circuit  150 ). Thus, during phase  1 , current flows from VCC through transistor  101  and inductor  104  to charge capacitor  105 . Also during phase  1 , transistors  111 ,  121  and  131  are turned off, and transistors  112 ,  122  and  132  are turned on. 
     During the next phase of operation (“phase 2”), phase control circuit  150  turns off transistor  101  and turns on transistor  102 . When transistor  102  is turned on and transistor  101  is turned off, current may continue to temporarily flow through inductor  104  to charge capacitor  105  since current flow through inductor  104  cannot change instantaneously. Transistor  102  provides a return path for this current. 
     Also during phase  2 , transistor  111  of switching regulator  110 B is turned on and transistor  112  is turned off. Consequently, similar to the previous discussion, capacitor  115  is charged by current flow from VCC through transistor  111 . Subsequent operations of switching regulators  510 C and  510 D during phases  3  and  4  are similar. 
     Phase control circuit  150  may be further configured to monitor the output voltage, Vout, at node  170  via a feedback control signal and adjust accordingly the duty cycle of transistors  101 ,  111 ,  121  and  131  to maintain a constant voltage level. 
     As stated previously, microprocessor  160  is configured to operate in a low power mode of operation. During such operation, microprocessor  160  requires less current. The low power mode of operation may be controlled by, for example, a power management unit (not shown), which detects certain system inactivity, as desired. Phase control circuit  150  is configured to selectively suspend operation of a subset of switching regulators  110  (e.g. switching regulators  110 B,  110 C and  110 D) upon assertion of a low power mode control signal which indicates that microprocessor  160  is currently operating in a low power mode. The low power mode control signal may be received from the power management unit. In this embodiment, phase control circuit  150  suspends operation of switching regulator circuits  110 B,  110 C and  110 D during the low power mode by removing (or otherwise driving or disabling) the control signals provided to the associated switching transistors  111 ,  112 ,  121 ,  122 ,  131  and  132  such that the transistors are held in an off state. During this mode, switching regulator  110 A operates in its normal manner as described previously. 
     In one embodiment, phase control circuit  150  includes an enable input, which when activated by an active enable signal  50  allows normal operation of phase control circuit  150 . However, when enable signal  50  is deactivated, phase control circuit  150  suspends operation of all switching regulator circuits  110 . In this particular embodiment, an active signal means a logic value of one, which corresponds to a voltage level of two volts or greater. A deactivated signal refers to a logic value of zero, which corresponds to a voltage level of less than 0.8 volts. It is noted that depending on the integrated circuit used, these voltage levels may be different. It is contemplated and intended that a variety of integrated circuits may be used and therefore a range of voltage levels may be used to satisfy the input voltage specifications on a particular integrated circuit. 
     The output of temperature sensitive circuit  10  is connected to the enable input of phase control circuit  150 . As described above in the description of FIG. 1, temperature sensitive circuit  10  may be a voltage divider circuit, which includes a thermistor  20  and a resistor  30 . The voltage developed at node  40  is dependent upon the selected resistance value of resistor  30  and the ambient resistance value of thermistor  20 . If the ambient temperature of thermistor  20  increases, the resulting decrease in the resistance value of thermistor  20  will cause a proportional decrease in the voltage at node  40 . Conversely, a decrease in the ambient temperature of thermistor  20  will cause an increase in the voltage at node  40 . Therefore, depending on the selected resistance value of resistor  30  and the range of resistance values that thermistor  20  can achieve, the voltage at node  40  may vary between zero volts and the maximum voltage level capable of developing across thermistor  20 . To achieve a particular ambient temperature voltage level at node  40 , proper resistance values must be calculated and chosen for resistor  30  and thermistor  20 . 
     As described in detail above, the voltage developed at node  40  of FIG. 2 is dependent on the resistance values chosen for resistor  30  and thermistor  20 . Hence, in this embodiment, resistance values are chosen such that at ambient operating temperature, the voltage at node  40  is above two volts, thus enabling phase control circuit  150  to provide switching control signals to switching regulator circuits  110 . 
     As will be described in more detail below, thermistor  20  is located such that it may detect a rise in a temperature corresponding to the ambient operating temperature of switching regulator circuits  110 . If the ambient operating temperature begins to increase, the resistance value of thermistor  20  will begin to decrease causing a proportional decrease of the voltage at node  140 . If the voltage decreases below the threshold of the enable input circuitry of phase control circuit  150 , then phase control circuit  150  will detect the enable signal as inactive and phase control circuit  150  will disable operation of switching regulator circuits  220 . This action will power down microprocessor  160 . Disabling the switching regulator circuits  110  and microprocessor  160  may advantageously reduce heat related damage to some computer system components. 
     If the ambient temperature begins to decrease, the resistance value of thermistor  20  will begin to increase causing a proportional increase of the voltage at node  40 . If the voltage increases above the threshold of the enable input circuitry of phase control circuit  150 , then phase control circuit  150  will detect the enable signal as active and phase control circuit  150  will enable operation of switching regulator circuits  110 . This action will power up microprocessor  160 . 
     Referring to FIG. 3, a diagram of one embodiment of a motherboard of a computer system including a power supply circuit is shown. Components that are identical to those shown in FIG.  1  and FIG. 2 are numbered identically for simplicity and clarity. A motherboard  300  includes a power supply circuit  100  and a microprocessor  160 . Power supply circuit  200  includes phase control circuit  150 , switching regulator circuits  110 A,  110 B,  110 C and  110 D and a thermistor  20 . 
     In this embodiment, thermistor  20  is located in close proximity to switching regulator circuits  110 A-D. The close proximity allows thermistor  20  to detect a temperature corresponding to the operating temperature of switching regulator circuits  110 A-D. It is noted that the location of thermistor  20  shown in FIG. 3 is an example only. It is contemplated that thermistor  20  may be located in other locations which may still allow detection of a temperature corresponding to the operating temperature of switching regulator circuits  220 A-D. 
     Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.