Patent Document

BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a power supply circuit. 
         [0003]    2. Description of Related Art 
         [0004]    A central processing unit (CPU) is an expensive and important part of an electronic device, such as a computer. When the CPU is damaged, the electronic device will no longer operate. A high input voltage can damage the CPU. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Many aspects of the present disclosure can be better understood with reference to the following 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 embodiments. 
           [0006]      FIG. 1  is a block diagram of an embodiment of a power supply circuit. 
           [0007]      FIG. 2  is a circuit diagram of the power supply circuit of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    The disclosure, including the accompanying drawings, is illustrated by way of examples and not by way of limitation. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one”. 
         [0009]      FIGS. 1 and 2  show an embodiment of a power supply circuit  10  to supply power to an electronic element  20 . The power supply circuit  10  includes a voltage conversion unit  12  and a voltage clamping unit  16 . The voltage conversion unit  12  is connected to the voltage clamping unit  16  and the electronic element  20 . The voltage conversion unit  12  is used to convert a voltage of a power supply into an operation voltage of the electronic element  20 , and output the converted voltage through an output terminal of the voltage conversion unit  12 . The voltage clamping unit  16  is used to clamp a voltage output from the output terminal of the voltage conversion unit  12  to the operation voltage of the electronic element  20 , when the voltage output from the output terminal of the voltage conversion unit  12  is more than the operation voltage of the electronic element  20 . In one embodiment, the power supply circuit  10  is assembled on a motherboard of a computer, and the electronic element  20  is a central processing unit. 
         [0010]    The voltage conversion unit  12  includes a driver chip  14 , two electronic switches Q 1  and Q 2 , two capacitors C 1  and C 2 , and an inductor L 1 . The driver chip  14  includes a first pin Hgate, a second pin Lgate, and a third pin Phase. Each of the electronic switches Q 1  and Q 2  includes a first terminal, a second terminal, and a third terminal. The first terminal of the electronic switch Q 1  is connected to the first pin Hgate of the driver chip  14 . The second terminal of the electronic switch Q 1  is connected to a power supply VIN, and grounded through the capacitor C 1 . The third terminal of the electronic switch Q 1  is grounded through the inductor L 1  and the capacitor C 2  in that order. The first terminal of the electronic switch Q 2  is connected to the second pin Lgate of the driver chip  14 . The second terminal of the electronic switch Q 2  is connected to the third terminal of the electronic switch Q 1 , and connected to the third pin Phase of the driver chip  14 . The third terminal of the electronic switch Q 2  is grounded. A node A between the inductor L 1  and the capacitor C 2  functions as an output terminal of the voltage conversion unit  12 , and is connected to the voltage clamping unit  16  and the electronic element  20 . 
         [0011]    The voltage clamping unit  16  includes a comparator U, an electronic switch Q 3 , an inductor L 2 , a diode D 1 , a capacitor C 3 , and four resistors R 1 -R 4 . The comparator U includes a non-inverting terminal, an inverting terminal, a power terminal, a ground terminal, and an output terminal. The non-inverting terminal of the comparator U is connected to a reference voltage Vref. The inverting terminal of the comparator U is connected to the output terminal of the voltage conversion unit  12  through the resistor R 1 , and grounded through the resistor R 2 . The power terminal of the comparator U is connected to a power supply VCC, and grounded through the capacitor C 3 . The ground terminal of the comparator U is grounded. The output terminal of the comparator U is connected to the power terminal of the comparator U through the resistor R 4 . The first terminal of the electronic switch Q 3  is connected to the output terminal of the comparator U through the resistor R 3 . The second terminal of the electronic switch Q 3  is grounded. The third terminal of the electronic switch Q 3  is connected to the output terminal of the voltage conversion unit  12  through the inductor L 2 . An anode of the diode D 1  is connected to the third terminal of the electronic switch Q 3 . A cathode of the diode D 1  is connected to the output terminal of the voltage conversion unit  12 . 
         [0012]    In one embodiment, each of the electronic switches Q 1  and Q 2  is an n-channel metal-oxide semiconductor field-effect transistor (NMOSFET), and the first terminal, the second terminal, and the third terminal of each of the electronic switches Q 1  and Q 2  respectively correspond to a gate, a drain, and a source of the NMOSFET. The electronic switch Q 3  is a pnp bipolar junction transistor (BJT), and the first terminal, the second terminal, and the third terminal of each of the electronic switches Q 3  respectively correspond to a base, a collector, and an emitter of the pnp BJT. A voltage of the inverting terminal of the comparator U complies with the following formula: V 1 =Vout×r 2 /(r 1 +r 2 ), where V 1  stands for the voltage of the inverting terminal of the comparator U, Vout stands for a voltage of the output terminal of the voltage conversion unit  12 , r 1  stands for a resistance of the resistor R 1 , and r 2  stands for a resistance of the resistor R 2 . The reference voltage Vref is a double data rate voltage termination (DDR_VTT) mode of operation supplied by the motherboard of the computer. The DDR_VTT is a half-operating voltage of the double data rate memory. In other embodiments, each of the electronic switches Q 1  and Q 2  may be an npn BJT, or another electronic switch having similar functions. The electronic switch Q 3  may be a p-channel metal-oxide semiconductor field-effect transistor, or another electronic switch having similar functions. 
         [0013]    In use, the first pin Hgate and the second pin Lgate of the driver chip  14  alternately output high level signals to turn on the electronic switches Q 1  and Q 2 . When the first pin Hgate outputs a high level signal, such as logic 1, and the second pin Lgate outputs a low level signal, such as logic 0, the electronic switch Q 1  is turned on, and the electronic switch Q 2  is turned off. The power supply VIN is filtered by the capacitor C 1 , then supplies power to charge the inductor L 1  and the capacitor C 2  through the electronic switch Q 1 . When the first pin Hgate outputs a low level signal, and the second pin Lgate outputs a high level signal, the electronic switch Q 1  is turned off, and the electronic switch Q 2  is turned on. The inductor L 1  and the capacitor C 2  are discharged through the electronic switch Q 2 . The output terminal of the voltage conversion unit  12  can then output the voltage Vout. 
         [0014]    When the voltage Vout of the output terminal of the voltage conversion unit  12  is equal to the operation voltage of the electronic element  20 , the voltage V 1  of the inverting terminal of the comparator U is less than the reference voltage Vref. The output terminal of the comparator U outputs a high level signal, and the electronic switch Q 3  is turned off. 
         [0015]    When the voltage Vout of the output terminal of the voltage conversion unit  12  is too high, because some elements of the motherboard are in abnormal conditions, such as a short circuit, the voltage V 1  of the inverting terminal of the comparator U is more than the reference voltage Vref. The output terminal of the comparator U outputs a low level signal, and thus the electronic switch Q 3  is turned on. The inductor L 2  is grounded through the electronic switch Q 3  to pull down the voltage Vout of the output terminal of the voltage conversion unit  12 , and the inductor L 2  is charged by the voltage Vout of the output terminal of the voltage conversion unit  12  at the same time. When the voltage Vout of the output terminal of the voltage conversion unit  12  is pulled down to the operation voltage of the electronic element  20 , the voltage V 1  of the inverting terminal of the comparator U is less than the reference voltage Vref. The output terminal of the comparator U outputs a high level signal, and the electronic switch Q 3  is turned off. The inductor L 2  is discharged through the diode D 1 . Therefore, the voltage Vout of the output terminal of the voltage conversion unit  12  is clamped and held to the operation voltage of the electronic element  20  by the voltage clamping unit  16 , to prevent damage to the electronic element  20  from a high input voltage. 
         [0016]    Even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

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