Abstract:
A measurement circuit for overload protection is applied in a buck circuit. The buck circuit includes a pulse width modulation (PWM) controller and a voltage output terminal. The measurement circuit includes a resistance setting circuit to connect different resistances to the PWM controller of the buck circuit. A switch circuit turns the measurement circuit on or off. A current collection circuit receives a voltage from the voltage output terminal of the buck circuit and transforms the received voltage to a current, and amplifies the transformed current and outputs the amplified current to the resistance setting circuit. The resistance setting circuit chooses a resistance through comparison of the amplified current with a preset current. A display unit displays the chosen resistance.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present disclosure relates to buck circuits, and particularly to a measurement circuit providing overload protection to a buck circuit. 
         [0003]    2. Description of Related Art 
         [0004]    Overload protection in a buck circuit is provided by connecting different resistors to the buck circuit manually, to generate optimal resistance for overload protection. However, the resistors must be individually soldered to corresponding locations, which is inconvenient and need extra man-hours. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Many aspects of the embodiments can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the several views. 
           [0006]      FIG. 1  is a circuit diagram for a buck circuit. 
           [0007]      FIGS. 2 and 3  are a circuit diagram of a measurement circuit providing overload protection for a buck circuit in accordance with an exemplary embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    The disclosure, including the drawings, is illustrated by way of example and not by 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 mean at least one. 
         [0009]    Referring to  FIG. 1  to  FIG. 3 , a measurement circuit  100  is configured to provide overload protection for a buck circuit  200 . The buck circuit  200  is mounted on a printed circuit board (not shown), and includes a pulse width modulation (PWM) controller  20 , a PWM driving unit  21 , two field effect transistors (FETs) Q 1  and Q 2 , a voltage input terminal Vin, and a voltage output terminal Vout. The PWM controller  20  is connected to the measurement circuit  100 . The PWM driving unit  21  is connected to the PWM controller  20  receiving a control signal from the PWM controller  20  and also connected to gates of the FETs Q 1  and Q 2  for outputting signals to turn the FETs Q 1  and Q 2  on or off. A drain of the FET Q 2  is connected to the voltage input terminal Vin. A source of the FET Q 1  is grounded. A drain of the FET Q 1  is connected to a source of the FET Q 2 . The drain of the FET Q 1  is also connected to one terminal of an inductor L and the other terminal of the inductor L is connected to one terminal of a capacitor C 0 . The other terminal of the capacitor C 0  is grounded. The voltage output terminal Vout is connected to a node between the inductance L and the capacitor C 0  for outputting a drive voltage to other elements (for example, central processor unit) and also connected to the measurement circuit  100 . 
         [0010]    The measurement circuit  100  in accordance with an exemplary embodiment includes a resistance setting circuit  110 , a switch circuit  120 , a current collection circuit  130 , and a display unit  140 . The resistance setting circuit  110  is configured to connect different resistors to the PWM controller  20  of the buck circuit  200 . The switch circuit  120  is configured to turn the measurement circuit  100  on or off. The current collection circuit  130  is configured to receive voltage from the voltage output terminal Vout of the buck circuit  200  and convert the received voltage to current, and amplify the converted current and provide the amplified current to the resistance setting circuit  110 . The resistance setting circuit  110  directs the display unit  140  to display the selected resistance. 
         [0011]    The resistor setting circuit  110  includes a microcontroller U 11 , a digital regulation resistance U 22 , a resistor R 1 , five capacitors C 1 -C 5 , and a crystal oscillator X 1 . Input terminals A 0 -A 3  of the digital regulation resistance U 22  are connected to output terminals RB 7 -RB 4  of the microcontroller U 11 . A clock terminal SCL of the digital regulation resistance U 22  is connected to an output terminal RB 3  of the microcontroller U 11 . A data terminal SDA of the digital regulation resistance U 22  is connected to an output terminal RB 2  of the microcontroller U 11 . A voltage terminal VCC of the digital regulation resistance U 22  is connected to a power source V 1  and connected to one terminal of the capacitor C 1 . The other terminal of the capacitor C 1  is grounded. Output terminals VH 0  and VW 0  of the digital regulation resistance U 22  are connected to the PWM controller  20 . Ground terminals VSS and VL 0  of the digital regulation resistance U 22  are grounded. A voltage terminal VDD of the microcontroller U 11  is connected to a power source VC, and connected to one terminal of the resistor R 1 . The other terminal of the resistor R 1  is connected to one terminal of the capacitor C 2 . The other terminal of the capacitor C 2  is grounded. One terminal of the capacitor C 3  is connected to the voltage terminal VDD of the microcontroller U 11  and the other terminal of the capacitor C 3  is grounded. A voltage terminal MP of the microcontroller U 11  is connected to a node between the resistor R 1  and the capacitor C 2 . A clock terminal OCS 1  of the microcontroller U 11  is grounded through the capacitor C 4 . A clock terminal OCS 2  of the microcontroller U 11  is grounded through the capacitor C 5 . The crystal oscillator X 1  is connected between the clock terminals OCS 1  and OCS 2  of the microcontroller U 11 . In one embodiment, microcontroller U 11  is a PIC16F73 and digital regulation resistance U 22  is X9241. The power source V 1  is a 5 volt (V) power source. 
         [0012]    The switch circuit  120  includes a resistor R 2  and a switch K 1 . An input terminal RA 1  of the microcontroller U 11  is connected to the power source VC through the resistor R 2  and also can be grounded through the switch K 1 . 
         [0013]    The current collection circuit  130  includes a transformer T 1 , a load  131 , amplifiers U 1 -U 3 , resistors R 3 -R 12 , and capacitors C 6 -C 9 . The load  131  is connected to the voltage output terminal Vout of the buck circuit  200  through the primary coil of the transformer T 1 . The resistor R 3  is connected between a first end and a second end of a secondary coil of the transformer T 1 . The first end of the secondary coil of the transformer T 1  is connected to a non-inverting input terminal of the amplifier U 1  through the resistor R 4 . The capacitor C 6  is connected between the non-inverting input terminal of the amplifier U 1  and ground. The capacitor C 7  is connected between the non-inverting input terminal and an inverting input terminal of the amplifier U 1 . The resistor R 5  is connected between the inverting input terminal and an output terminal of the amplifier U 1 . The output terminal of the amplifier U 1  is connected to an inverting input terminal of the amplifier U 3  through the resistor R 6 . The resistor R 7  is connected between the inverting input terminal and an output terminal of the amplifier U 3 . The resistor R 8  is connected between the inverting input terminal of the amplifier U 1  and an inverting input terminal of the amplifier U 2 . The resistor R 9  is connected between the inverting input terminal and an output terminal of the amplifier U 2 . The second end of the secondary coil of the transformer T 1  is connected to a non-inverting input terminal of the amplifier U 2  through the resistor R 10 . The capacitor C 9  is connected between the non-inverting terminal of the amplifier U 2  and ground. The capacitor C 8  is connected between the inverting input terminal and the non-inverting input terminal of the amplifier U 2 . The output terminal of the amplifier U 2  is connected to the non-inverting input terminal of the amplifier U 3  through the resistor R 11 . The resistor R 12  is connected between the non-inverting input terminal of the amplifier U 3  and ground. The output terminal of the amplifier U 3  is connected to an input terminal RA 0  of the microcontroller U 11 . Ground terminals of the amplifiers U 1 -U 3  are grounded. Voltage terminals of the amplifier U 1 -U 3  are connected to a power source V 2 . In one embodiment, the power source V 2  is a 12V power source, and the transformer T 1  is a current collecting transformer. 
         [0014]    The display unit  140  is connected to input/output (I/O) terminals RA 2 -RA 5  and RC 0 -RC 7  of the microcontroller U 11 . 
         [0015]    In one embodiment, the output terminals RB 4 -RB 7  of the microcontroller U 11  have sixteen kinds of output. Each output can control a corresponding resistance of the digital regulation resistance U 22  to be connected to the buck circuit  200 . For example, the output terminals RB 4 -RB 7  of the microcontroller U 11  output signals “0000”, to direct the digital regulation resistance U 22  to provide a 0.5Ω resistance to the buck circuit  200 , wherein “0” indicates a low level signal. When the output terminals RB 4 -RB 7  of the microcontroller U 11  output signals “0001”, to direct the digital regulation resistance U 22  to provide a 1Ω resistance to the buck circuit  200 , wherein “1” indicates a high level signal. 
         [0016]    In use, when the switch K 1  is pressed to close, the microcontroller U 11  is turned on. The output terminals RB 4 -RB 7  of the microcontroller U 11  output signals “0000” to the digital regulation resistance U 22 , to direct the digital regulation resistance U 22  to provide a 0.5Ω resistance to the buck circuit  200 . The PWM controller  20  outputs a PWM signal to the PWM driving unit  21 , to turn the FETs Q 1  and Q 2  on or off. The voltage output terminal Vout outputs a voltage to other elements. At the same time, the voltage from the voltage output terminal Vout is provided to the primary coil of the transformer T 1 , and is also provided to the load  131 . The voltage across the primary coil of the transformer T 1  induces a current in the secondary coil of the transformer T 1  and a voltage is maintained across the resistor R 3 , the induced current is amplified through the amplifiers U 1 -U 3  and the output current of the amplifiers U 1 -U 3  is provided to the microcontroller U 11  through the input terminal RA 0 . The microcontroller U 11  compares the amplified current with a preset current and directs the display unit  140  to display the 0.5Ω resistance. If the amplified current is less than the preset current, the output terminals RB 4 -RB 7  of the microcontroller U 11  output signals, such as “0001” to the digital regulation resistance U 22 , to direct the digital regulation resistance U 22  to provide increased resistance, such as 1Ω resistance to the buck circuit  200 , and the work theory is same as described. If the amplified current exceeds the preset current, the microcontroller U 11  outputs no control signals to the digital regulation resistance U 22 . The PWM controller  20  will not output a PWM signal. The voltage output terminal Vout outputs no voltage. Thus, the last resistance displayed on the display unit  140  is an optimal overload protection for the buck circuit  200 . 
         [0017]    The measurement circuit  100  can obtain an overload protection optimal resistance of the buck circuit  200  by automatically connecting different resistances to the buck circuit  200 . The measurement circuit  100  is simple and can save costs. 
         [0018]    It is to be understood, however, that 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 invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.