Abstract:
A switchable voltage regulation circuit includes a power supply chip and a voltage regulation module. The voltage regulation module includes first and second resistors and first and second switch units. A first terminal of the first resistor is electrically coupled to a power supply and a first output pin of the power supply chip. A first terminal of the second resistor is electrically coupled to the second terminal of the first resistor. The first switch unit is electrically coupled between the first terminal of the first resistor and the second terminal of the first resistor. The second switch unit is electrically coupled between the first terminal of the second resistor and the voltage output. By manual switching, or by transistors under control of a baseboard management unit, the resistances can be switched in or switched out to regulate the voltage.

Description:
FIELD 
     The subject matter herein generally relates to voltage regulation. 
     BACKGROUND 
     When a server is tested, an output voltage of a motherboard will be adjusted to a maximal voltage, and the motherboard is installed in the server to test the server. After the server is tested at maximal voltage, the motherboard is removed from the server, and the output voltage of the motherboard will be adjusted to a minimum voltage through changing resistances. Then the motherboard is installed in the server to test the server again at minimal voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
         FIG. 1  is a circuit diagram of a first embodiment of a voltage regulation circuit. 
         FIG. 2  is a circuit diagram of a second embodiment of a voltage regulation circuit. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the like. 
     The present disclosure relates to a voltage regulation circuit. 
       FIG. 1  illustrates an exemplary embodiment of a voltage regulation circuit. The voltage regulation circuit is configured to test an output voltage of a motherboard. The voltage regulation circuit comprises a power supply chip  40 , a resistor R 1 , and a voltage regulation module  10 . 
     The power supply chip  40  comprises an output pin VFB to provide a reference voltage Vf. 
     The voltage regulation module  10  comprises three resistors, R 2 -R 4 , and two switch units,  11  and  13 . The voltage regulation module  10  is electrically coupled to ground, and is electrically coupled to a voltage output V OUT . The switch unit  11  can comprise a single-pole single-throw switch SW 1 , and the switch unit  13  can comprise a single-pole single-throw switch SW 2 . 
     A first terminal of the resistor R 1  is electrically coupled to a power supply P 5 V, and a second terminal of the resistor R 1  is electrically coupled to the output pin VFB of the power supply chip  40 , to a second terminal of the resistor R 2 , and to a first terminal of the switch SW 1 . A second terminal of the resistor R 2  is electrically coupled to a first terminal of the resistor R 4 , and to a node between a second terminal of the resistor R 3  and a first terminal of the switch SW 2 . A first terminal of the resistor R 3  is electrically coupled to a second terminal of the switch SW 1 . The second terminals of the resistors R 3  and R 2  are electrically coupled to the first terminal of the resistor R 4 . A second terminal of the resistor R 4  and a second terminal of the switch SW 2  are electrically coupled to ground through a capacitor C, and are electrically coupled to the voltage output V OUT . 
     When the switch SW 1  is turned off and the switch SW 2  is turned on, the resistor R 4  is short circuited, and the resistor R 1  and the resistor R 2  work in series. The power supply P 5 V and the reference voltage Vf are output from the voltage output V OUT  through the resistors R 1  and R 2 , and the voltage output from the voltage output V OUT  is a normal working voltage of the motherboard. 
     When the switch SW 1  is turned on and the switch SW 2  is turned off, the resistor R 2  and the resistor R 3  work in parallel, and the resistor R 1 , the resistor R 2 , and the resistor R 4  are in series. The power supply P 5 V and the reference voltage Vf are output from the voltage output V OUT  through the resistors R 1 -R 4 , and the voltage output from the voltage output V OUT  is a maximal working voltage of the motherboard. 
     When the switches SW 1  and SW 2  are both turned off, the resistor R 1 , the resistor R 2 , and the resistor R 4  work in series. The power supply P 5 V and the reference voltage Vf are output from the voltage output V OUT  through the resistors R 1 , R 2 , and R 4 , and the voltage output from the voltage output V OUT  is a minimum working voltage of the motherboard. 
     In at least one embodiment, a voltage value of the power supply P 5 V can be 5V, and a voltage value of the reference voltage Vf can be 0.6V. A resistance of the resistor R 1  can be 14.2KΩ, a resistance of the resistor R 2  can be 2 KΩ, a resistance of the resistor R 3  can be 22K Ω, and a resistance of the resistor R 4  can be 53.6 KΩ. The maximal working voltage value output from the voltage output V OUT  can be 5.25V, and the minimum working voltage value from the voltage output V OUT  can be 4.75V. In other embodiments, the resistance of the resistors R 3  and R 4  can be changed according to need, to adjust the maximal working voltage and the minimum working voltage output from the voltage output V OUT . 
       FIG. 2  illustrates a second exemplary embodiment of a voltage regulation circuit. The voltage regulation circuit comprises a power supply chip  40 , a resistor R 1 , a voltage regulation module  20 , and a BMC (Baseboard Management Controller)  30 . 
     The power supply chip  40  comprises an output pin VFB to provide a reference voltage Vf. 
     The voltage regulation module  20  comprises three resistors R 2 -R 4  and two switch units  21  and  23 . The voltage regulation module  20  is electrically coupled to ground, and is electrically coupled to a voltage output V OUT . The switch unit  21  can comprise an electronic switch Q 1 , and the switch unit  23  can comprise an electronic switch Q 2 . 
     The BMC  30  comprises two output pins OUT 1  and OUT 2 . The output pins OUT 1  and OUT 2  are respectively electrically coupled to a first terminal of the electronic switch Q 1  and to a first terminal of the electronic switch Q 2 , to output a control signal to the electronic switch Q 1  and to the electronic switch Q 2  respectively. 
     A first terminal of the resistor R 1  is electrically coupled to a power supply P 5 V, and a second terminal of the resistor R 1  is electrically coupled to the output pin VFB of the power supply chip  40 , to a second terminal of the resistor R 2 , and to a second terminal of the electronic switch Q 1 . A second terminal of the resistor R 2  is electrically coupled to a first terminal of the resistor R 4  and to a second terminal of the electronic switch Q 2 . A first terminal of the resistor R 3  is electrically coupled to a third terminal of the electronic switch Q 1 . A second terminal of the resistor R 3  is electrically coupled to the second terminal of the electronic switch Q 2 , to the second terminal of the resistor R 2 , and to the first terminal of the resistor R 4 . A second terminal of the resistor R 4  and a third terminal of the electronic switch Q 2  are electrically coupled to ground through a capacitor C, and are electrically coupled to the voltage output V OUT . 
     In at least one embodiment, each of the electronic switches Q 1  and Q 2  can be n-channel metal-oxide semiconductor field-effect transistors (NMOSFET), and the first terminal, the second terminal, and the third terminal of the electronic switches Q 1  and Q 2  correspond to a gate, a drain, and a source of the NMOSFET. 
     The BMC  30  can start a first control program, a second control program, or a third control program according to a default program in the BMC  30 . The BMC  30  controls the output pins OUT 1  and OUT 2  to output a high level signal or a low level signal to the electronic switches Q 1  and Q 2 . When the BMC  30  starts the first control program, the BMC  30  controls the output pin OUT 1  to output a low level signal to the first terminal of the electronic switch Q 1 , and the BMC  30  controls the output pin OUT 2  to output a high level signal to the first terminal of the electronic switch Q 2 . The electronic switch Q 1  is turned off and the electronic switch Q 2  is turned on. The resistor R 4  is short circuited, and the resistor R 1  and the resistor R 2  are in series. The power supply P 5 V and the reference voltage Vf are output from the voltage output V OUT  through the resistors R 1  and R 2 , and the voltage output from the voltage output V OUT  is a normal working voltage of the motherboard. 
     When the BMC  30  starts the second control program, the BMC  30  controls the output pin OUT 1  to output the high level signal to the first terminal of the electronic switch Q 1 , and the output pin OUT 2  to output the low level signal to the first terminal of the electronic switch Q 2 . The electronic switch Q 1  is turned on, and the electronic switch Q 2  is turned off. The resistor R 2  and the resistor R 3  are in parallel, and the resistor R 1 , the resistor R 2 , and the resistor R 4  are in series. The power supply P 5 V and the reference voltage Vf are output from the voltage output V OUT  through the resistors R 1 -R 4 , and the voltage output from the voltage output V OUT  is a maximal working voltage of the motherboard. 
     When the BMC  30  starts the third control program, the BMC  30  controls the output pin OUT 1  to output the low level signal to the first terminal of the electronic switch Q 1 , and the output pin OUT 2  to output the low level signal to the first terminal of the electronic switch Q 2 . The electronic switch Q 1  is turned off, and the electronic switch Q 2  is turned off. The resistor R 1 , the resistor R 2 , and the resistor R 4  are in series. The power supply P 5 V and the reference voltage Vf are output from the voltage output V OUT  through the resistors R 1 , R 2 , and R 4 , and the voltage output from the voltage output V OUT  is a minimum working voltage of the motherboard. 
     In the illustrated embodiment, a voltage value of the power supply P 5 V can be 5V, and a voltage value of the reference voltage Vf can be 0.6V. A resistance of the resistor R 1  can be 14.2 KΩ, a resistance of the resistor R 2  can be 2 KΩ, a resistance of the resistor R 3  can be 22 KΩ, and a resistance of the resistor R 4  can be 53.6 KΩ. The maximal working voltage value output from the voltage output V OUT  can be 5.25V, and the minimal working voltage value from the voltage output V OUT  can be 4.75V. In other embodiments, the resistances of the resistors R 3  and R 4  can be changed according to need, to adjust the maximal working voltage and the minimal working voltages output from the voltage output V OUT . 
     The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the details, including matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims.