Patent Publication Number: US-8987934-B2

Title: Power supply with extended minimum voltage output

Description:
TECHNICAL FIELD 
     Various exemplary embodiments disclosed herein relate generally to regulated power supplies. 
     BACKGROUND 
     A voltage regulator is an electrical component designed to automatically output a constant voltage level to a load. Voltage regulators are able to output a constant voltage level when a voltage input to the regulator is above a minimum threshold. The minimum threshold is typically much larger than the constant voltage level the regulator is designed to output. In a low-dropout (LDO) regulator, the minimum threshold of the input voltage is closer to the voltage level of the output voltage, but remains some amount higher than the output voltage. When the input voltage falls below the minimum threshold of the regulator, the regulator may no longer function as designed. 
     SUMMARY 
     A brief summary of various exemplary embodiments is presented. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various exemplary embodiments, but not to limit the scope of the invention. Detailed descriptions of a preferred exemplary embodiment adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections. 
     Various exemplary embodiments relate to system for supplying power including: a power source outputting a source voltage; a first regulator connected to the power source, wherein the first regulator outputs a first voltage when the source voltage is above a minimum threshold; and an extension module connected to the power source, wherein the extension module outputs a second voltage when the source voltage falls below the minimum threshold. 
     Various exemplary embodiments further relate to a method for supplying power including: outputting a source voltage from a power source; connecting a first regulator to the power source, wherein the first regulator outputs a first voltage when the source voltage is above a minimum threshold; and connecting an extension module to the power source, wherein the extension module outputs a second voltage when the source voltage falls below the minimum threshold. 
     In some embodiments, the first regulator is a low-dropout regulator. In some embodiments, the extension module shares circuit components with the low-dropout regulator. In some embodiments, the shared circuited components are transistors forming a current mirror. In some embodiments, the system for supplying power further includes: a microcontroller having a memory and processor core, wherein the second voltage is below a minimum voltage requirement of the processor core and above a minimum voltage requirement of the memory. In some embodiments, the first regulator is disabled when the source voltage falls below the minimum threshold, and wherein the extension module is disabled when the source voltage is above the minimum threshold. In some embodiments, the system for supplying power further includes: a second regulator for supplying a signal to the first regulator and the extension module, wherein the signal disables the first regulator and enables the extension module when the source voltage falls below the minimum threshold. In some embodiments, the first regulator, second regulator, and extension module are integrated on a system chip. In some embodiments, the power source is vehicle battery. In some embodiments, the source voltage falls below the minimum threshold upon the starting of a vehicle engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand various exemplary embodiments, reference is made to the accompanying drawings, wherein: 
         FIG. 1  illustrates an embodiment of a conventional system for supplying power. 
         FIG. 2  illustrates an embodiment of a conventional low-dropout regulator. 
         FIG. 3  illustrates an embodiment of a system for supplying power. 
         FIG. 4  illustrates an embodiment of an extension module. 
         FIG. 5  illustrates an alternate embodiment of a low-dropout regulator. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like components or steps, there are disclosed broad aspects of various exemplary embodiments. 
     It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principals of the embodiments of the invention. 
     According to the foregoing, various exemplary embodiments provide for a system and method for a power supply with an extended minimum voltage output. 
       FIG. 1  illustrates an embodiment of a conventional system  100  for supplying power to a microcontroller  102 . A power source  104  may be connected to a system chip  106 . The system chip  106  may include an internal supply regulator  108  and a low-dropout (LDO) regulator  110  for regulating the power supplied to the microcontroller  102 . The microcontroller  102  may include a memory  112  and a processor core  114 . 
     The power source  104  may be a battery or other source for supplying a direct current voltage Vin. In some embodiments, the power source  104  may be, for example, a 12V car battery. A diode D 1  may be connected in series between the power source  104  and the system chip  106 . A capacitor Cin may be connected between ground and a node between the diode D 1  and the system chip  106 . A capacitor Cdd may be connected between ground and a node between the system chip  106  and the microcontroller  102 . 
     The voltage (Vin) supplied by the power source  104  may be routed to the internal supply regulator  108  and the LDO regulator  110  in the system chip  106 . The internal supply regulator  108  may be used to distribute regulated power and signals to other components of the system chip  106 . When Vin is above a minimum threshold, the internal supply regulator  108  may output a power-on-reset (POR) signal and an internal supply voltage (Vint) to the LDO regulator  110 . The POR signal may be used to enable or disable the LDO regulator  110 . When the LDO regulator  110  is enabled, it may output a voltage Vdd to the microcontroller  102 . The voltage Vdd may be routed to the memory  112  and the processor core  114  of the microcontroller  102 . 
     In some embodiments, the system  100  may include components of a vehicle. The power source  104  may be, for example, a 12V car battery. The system chip  106  may be used to regulate the voltage from the 12V car battery to a lower voltage level that is safe for other components in the vehicle, such as, for example, the microcontroller  102 . The voltage supplied by the 12V car battery may vary as the battery is used with other parts of the vehicle. For example, during the starting of a vehicle engine, the voltage supplied by 12V car battery may drop below 3V. 
     The memory  112  in the microcontroller  102  may operate at a lower voltage than the processor core  114  (for example, 2V for the memory and 3V for the core). The lower voltage requirement for the memory  112  may allow the memory to keep stored content valid during power reductions, such as, for example, during the starting of a vehicle engine. However, in the conventional system  100 , the LDO regulator  110  may be unable to output the voltage Vdd when the voltage supplied by the power source  104  (Vin) is reduced below a minimum threshold. For example, the internal supply regulator  108  may have a minimum Vin voltage requirement of 3V. If a lower Vin voltage of 2V is supplied by the power source  104 , the internal voltage regulator  108  may stop outputting the POR signal. When the POR signal is low, the LDO regulator may be disabled, and no voltage Vdd may be supplied to the microcontroller  102 . Alternatively, the LDO regulator  110  may have a minimum Vin voltage requirement itself and may no longer output the voltage Vdd upon Vin dropping below the minimum requirement. When the voltage Vdd is no longer supplied to the microcontroller, the memory  112  may be reset. 
       FIG. 2  illustrates an embodiment of the conventional LDO regulator  110 . The LDO regulator  110  may include a high-voltage current mirror (T 1 , T 2 ), a driver transistor (T 3 ), and a transconductance amplifier (A 1 ) in a negative feedback configuration. Two resistors (R 1 , R 2 ) may be used to bias the amplifier (A 1 ). The LDO regulator  110  may be powered down by the POR signal, which may control a switch (SW 1 ) connecting the low-voltage Vint signal to the amplifier (A 1 ). 
       FIG. 3  illustrates a system  300  for supplying power to a microcontroller  302  according to an embodiment of the present invention. A power source  304  may be connected to a system chip  306 . The system chip  306  may include an internal supply regulator  308 , a low-dropout (LDO) regulator  310 , and an extension module  311  for regulating the power supplied to the microcontroller  302 . The extension module  311  may be a separate component or integrated in the LDO regulator  310 . 
     The microcontroller  302  may include a memory  312  and a processor core  314 . The power source  304  may be a battery or other source for supplying a direct current voltage Vin. In some embodiments, the power source  304  may be, for example, a 12V car battery. A diode D 1  may be connected in series between the power source  304  and the system chip  306 . A capacitor Cin may be connected between ground and a node between the diode D 1  and the system chip  306 . A capacitor Cdd may be connected between ground and a node between the system chip  306  and the microcontroller  302 . 
     The voltage (Vin) supplied by the power source  304  may be routed to the internal supply regulator  308 , the LDO regulator  310 , and the extension module  311  in the system chip  306 . The internal supply regulator  308  may be used to distribute regulated power and signals to other components of the system chip  306 . When Vin is above a minimum threshold, the internal supply regulator  308  may output a power-on-reset (POR) signal to the LDO regulator  310  and the extension module  311 . The internal supply regulator may also output an internal supply voltage (Vint) to the LDO regulator  310 . The POR signal may be used to enable or disable the LDO regulator  310  and the extension module  311 . The LDO regulator  310  and extension module  311  may output a voltage Vdd to the microcontroller  302 . The voltage Vdd may be routed to the memory  312  and the processor core  314  of the microcontroller  302 . 
     Similar to the conventional system  100 , in some embodiments the system  300  illustrated in  FIG. 3  may include components of a vehicle. The power source  304  may be, for example, a 12V car battery. The system chip  306  may be used to regulate the voltage from the 12V car battery to a lower voltage level that is safe for other components in the vehicle, such as, for example, the microcontroller  302 . The voltage supplied by the 12V car battery may vary as the battery is used with other parts of the vehicle. For example, during the starting of a vehicle engine, the voltage supplied by 12V car battery may drop below 3V. 
     Unlike the conventional system  100 , the system  300  illustrated in  FIG. 3  may continue to supply a voltage Vdd to the microcontroller  302  when the Vin voltage supplied by the power source  304  is below the minimum voltage requirement of the internal supply regulator  308  and the LDO regulator  310 . For example, the internal supply regulator  308  may have a minimum Vin voltage requirement of 3V, as described above. If a lower Vin voltage of 2V is supplied by the power source  304 , the internal voltage regulator  308  may stop outputting the POR signal. When the POR signal is low, the LDO regulator may be disabled, and the extension module  311  may be enabled. The extension module  311  may then continue supplying a Vdd voltage to the microcontroller  302 . The extension module  311  may supply a voltage Vdd to the microcontroller  302  that is lower than the Vdd voltage normally output by the LDO regulator  310 . The Vdd voltage supplied by the extension module  311 , while lower than normally output by the LDO regulator  310 , may be capable of preventing the memory  312  from being reset. For example, the LDO regulator  310  may be disabled when Vin drops to 2.5V, but the extension module  311  may continue to supply a Vdd voltage of greater than 2V to the microcontroller  302 . If the memory has a minimum voltage requirement of 2V, then the data stored in the memory may be preserved. 
       FIG. 4  illustrates an embodiment of the extension module  311 . When the power source voltage Vin is above the minimum supply voltage of the internal supply regulator  308  and LDO regulator  310  (for example, Vin&gt;3V), the internal supply regulator  308  may output a high POR signal. The high POR signal may enable the LDO regulator  310  and may disable the extension module  311  by activating transistor T 3 , as illustrated in  FIG. 4 . When the power source voltage Vin drops below the minimum supply voltage of the internal supply regulator  308  and LDO regulator  310  (for example, Vin&lt;3V), the LDO regulator  310  may be disabled by a low POR signal and the extension module  311  may be enabled by deactivating transistor T 3 . Resistor R 1  may activate a current reference circuit built around transistors T 4  and T 5  and resistor R 2 . The drain current of transistor T 4  may be amplified by a current mirror formed by transistors T 1  and T 2  such that the minimum output current may be higher than the current required by the memory  312  in the microcontroller  302 . With this topology a normal-on current source may be created. The current reference transistor T 4  may be active only with a certain minimum voltage at the Vdd output of the system chip  306 , because the drain current of transistor T 5  may be supplied out of the Vdd output pin via resistor R 1 . This may result in the extension module  311  not being active when the voltage Vin supplied by the power source  304  is increasing from 0V. However, the extension module  311  may be active when the voltage Vin supplied by the power source  304  is decreasing below the minimum voltage requirement of the internal supply regulator  308  and LDO regulator  310 . By activating the extension module  311  when Vin is falling, the data stored in the memory  312  may be preserved as long as the voltage Vdd is greater than the minimum voltage requirement of the memory  312 . 
       FIG. 5  illustrates an alternate embodiment of an LDO regulator  500  with an integrated extension module  502 . Some components of the conventional LDO regulator  110 , as shown in  FIG. 2 , may be reused as components of the extension module  502 , namely the output current mirror (T 1 ,T 2 ) and the feedback resistors (R 1 ,R 2 ). The transistors T 1  and T 2  may form a current source when used by the extension module  502 . The extension module  502  may further include a current reference formed by transistors T 4  and T 5  and resistor R 3 , and a switch formed by transistor T 6 . 
     The circuit may operate similar to the standalone extension module  311  described above. When the power source voltage Vin is above the minimum supply voltage of the internal supply regulator  308  and LDO regulator  310  (for example, Vin&gt;3V), the internal supply regulator  308  may output a high POR signal. The high POR signal may enable the LDO regulator  310  and may disable the extension module  502  by activating transistor T 6 , as illustrated in  FIG. 5 . When the power source voltage Vin drops below the minimum supply voltage of the internal supply regulator  308  (for example, Vin&lt;3V), the LDO regulator  500  may be disabled by a low POR signal and the extension module  502  may be enabled by deactivating transistor T 6 . Resistors R 1  and R 2  may activate the current reference circuit built around transistors T 4  and T 5  and resistor R 3 . The drain current of transistor T 4  may be amplified by a current mirror formed by transistors T 1  and T 2  such that the minimum output current is higher than the current required by the memory  312  in the microcontroller  302 . With this topology a normal-on current source may be created. The current reference transistor T 4  may be active only with a certain minimum voltage at the Vdd output of the system chip  306 , because the drain current of transistor T 5  may be supplied out of the Vdd output pin via resistors R 1  and R 2 . This may result in the extension module  502  not being active when the voltage Vin supplied by the power source  304  is increasing from 0V. However, the extension module  502  may be active when the voltage Vin supplied by the power source  304  is decreasing below the minimum voltage requirement of the internal supply regulator  308 . By activating the extension module  502  when Vin is falling, the data stored in the memory  312  may be preserved as long as the voltage Vdd is greater than the minimum voltage requirement of the memory  312 . 
     Although the various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be affected while remaining within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the invention, which is defined only by the claims.