Abstract:
An energy-efficient power control device, which employs a snubber circuit only during the risk of voltage spikes during fast switching, includes a buck converter, a power supply unit (PSU), a peak detecting circuit, a snubber circuit, and a logic circuit. The power control device supplies power to an input terminal of an electronic device. The snubber circuit is connected to the buck converter. The logic circuit is connected between the peak detecting circuit and the snubber circuit and determines whether the buck converter is under the heavy load or a light load according to the voltage, and connects the snubber circuit when the buck converter is under the heavy load, and disconnects the snubber circuit when the buck converter is under the light load.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure generally relates to power control devices, and more particularly, to a power control device including a snubber circuit. 
         [0003]    2. Description of the Related Art 
         [0004]    A typical power control device of electronic devices includes a power supply unit (PSU) and a buck converter. The PSU supplies direct current (DC). The buck converter converts the DC voltage of the PSU down to one or more preset voltages which may be supplied to the electronic device. A typical buck converter includes a first switch and a second switch alternately closing and opening. When the buck converter is under a heavy load (for example, when the output voltage of the PSU is high (e.g., greater than 20 volts)), the first switch and the second switch turn on and turn off at a high frequency which would result in generation of a voltage spike that may damage the first switch and the second switch. 
         [0005]    A commonly used snubber circuit includes a resistor and a capacitor connected in series, and the snubber circuit is connected in parallel with the second switch to decrease the voltage spike. However, when the buck converter is under a light load (for example, when the output voltage of the PSU is low (e.g., less than 10 volts), the snubber circuit is idle and increases power loss of the power control device. 
         [0006]    Therefore, there is room for improvement within the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Many aspects of an exemplary power control device 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 exemplary power control device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment. 
           [0008]      FIG. 1  is a circuit diagram of a power control device, according to an exemplary embodiment. 
           [0009]      FIG. 2  is a circuit diagram of a peak detecting circuit of the power control device of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is a circuit of power control device  100  of one embodiment. The power control device  100  supplies power to an input terminal  200  of an electronic device (not shown). The power control device  100  includes a buck converter  10 , a power supply unit (PSU)  12 , a peak detecting circuit  30 , a snubber circuit  50 , and a logic circuit  70 . The PSU  12  provides a direct current voltage Vin to the buck converter  10 . The buck converter  10  includes a controller  11  which is utilized to output a stable working voltage for the input terminal  200 . The peak detecting circuit  30  is electronically connected between the buck converter  10  and the logic circuit  70 . The peak detecting circuit  30  detects a voltage Vx of the buck converter  10 . The buck converter  10  provides the voltage Vx to a load (not shown) of the input terminal  200 . The voltage Vx varies with the load presented by the input terminal  200 . For example, if the load of the input terminal  200  becomes greater, the voltage Vx must become greater to make sure that the input terminal  200  is in a normal working state. 
         [0011]    The snubber circuit  50  is electrically connected to the buck converter  10 . The logic circuit  70  is electrically connected to the snubber circuit  50  and defines a reference voltage value Vref. The logic circuit  70  compares the reference voltage value Vref with the voltage Vx detected by the peak detecting circuit  30  to generate a comparison and controls the snubber circuit  50  to work or to stop working based on the result of the comparison. 
         [0012]    When the peak detecting circuit  30  detects that the voltage Vx is high, the logic circuit  70  determines that the buck converter  10  is under a heavy load and controls the snubber circuit  50  to work so as to protect the buck converter  10 . When the peak detecting circuit  30  detects that the voltage Vx is low, the logic circuit  70  determines that the buck converter  10  is under a light load and controls the snubber circuit  50  to stop working so as to cancel the drain of power taken by the snubber circuit  50  itself. 
         [0013]    The buck converter  10  includes the controller  11 , a first switch Q 1 , a second switch Q 2 , an inductor L, and a filter capacitor C 1 . In this embodiment, the first switch Q 1  and the second switch Q 2  are field-effect transistors. Gate electrodes of the first switch Q 1  and the second switch Q 2  are electronically connected to the controller  11 . The controller  11  adjusts voltages of the gate electrodes to selectively close or open the first switch Q 1  and the second switch Q 2 . In this embodiment, the controller  11  is a pulse width modulation integrated circuit (PWM IC) chip. The controller  11  sends pulse width modulation signals to the first switch Q 1  and the second switch Q 2 , and adjusts duty ratio of the pulse width modulation signals to regulate turn-on times of the first switch Q 1  and the second switch Q 2 . 
         [0014]    The first switch Q 1  and the second switch Q 2  are connected in series between the PSU  12  and the ground to obtain a node  13  between the first switch Q 1  and the second switch Q 2 , and a voltage of the node  13  is equal to the voltage Vx. A drain electrode of the first switch Q 1  is electronically connected to the PSU  12 , and a source electrode of the first switch Q 1  is electronically connected to a drain of the second switch Q 2 . A source electrode of the second switch Q 2  is grounded. A first end of the inductor L is electronically connected to the drain electrode of the second switch Q 2 , and a second end of the inductor L is electronically connected to ground through the filter capacitor C 1 . The input terminal  200  is connected in parallel with the filter capacitor C 1 . 
         [0015]    When the controller  11  allows the first switch Q 1  to close (turn on), and allows the second switch Q 2  to open (turn off), the PSU  12  provides power to the input terminal  200  via the first switch Q 1  and the inductor L, and the inductor L stores electromagnetic energy. When the controller  11  allows the first switch Q 1  to open (turn off), and allows the second switch Q 2  to close (turn on), the inductor L acts like a voltage source and provides power to the input terminal  200 . Therefore, the first switch Q 1  alternately opens or closes and the voltage Vx is generated as PWM signals as shown in  FIG. 2 . 
         [0016]    The peak detecting circuit  30  defines a detecting terminal  301  and an output terminal  302 . The detecting terminal  301  is electrically connected to the node  13  of the buck converter  10  and is utilized to detect the voltage Vx. The output terminal  302  is electrically connected to the logic circuit  70 . As shown in  FIG. 2 , the peak detecting circuit  30  converts the voltage Vx having an irregular waveform into an output voltage Vout having a sawtooth and more regular waveform and the output terminal  302  outputs the output voltage Vout. 
         [0017]    In the embodiment, a time difference between peaks of the sawtooth waveform is very small and the output voltage Vout is similar to a smooth and constant voltage. In other words, the peak detecting circuit  30  converts the voltage Vx into a DC voltage Vout, the DC voltage Vout is proportional to the peak value of the voltage Vx, therefore, as the peak value of the voltage Vx becomes greater, the output voltage Vout also becomes greater. The logic circuit  70  compares the output voltage Vout with the reference voltage value Vref to determine whether the buck converter  10  is under a heavy load or the light load. 
         [0018]    Referring to  FIG. 2 , the peak detecting circuit  30  includes a follower  31 , an amplifier  32 , and an RC circuit  33 . The RC circuit  33  is an integral circuit. The RC circuit  33  is composed of a resistor Ra and a capacitor Ca connected in parallel. The follower  31  tracks the voltage Vx to be integrated within the RC circuit  33  and outputs the sawtooth waveform voltage Vout to the logic circuit  70 . 
         [0019]    The snubber circuit  50  includes a resistor R and a snubber capacitor C 2  connected in series. The drain electrode of the second switch Q 2  is connected to the resistor R. The snubber capacitor C 2  is connected to ground via the logic circuit  70 . 
         [0020]    The logic circuit  70  includes a comparator  71  and a control switch  73 . The comparator  71  includes a first input terminal  701 , a second input terminal  702 , and an output terminal  703 . The control switch  73  includes a control terminal  731 , a first open terminal  732 , and a second open terminal  733 . The first input terminal  701  is electrically connected to the output terminal  302  of the peak detecting circuit  30 . The second input terminal  702  is electrically connected to the reference voltage Vref. The output terminal  703  is electrically connected to the control terminal  731 . The first open terminal  732  is electrically connected to the snubber capacitor C 2  and the second open terminal  733  is grounded. 
         [0021]    The comparator  71  compares the output voltage Vout of the peak detecting circuit  30  with the reference voltage Vref. When the output voltage Vout of the peak detecting circuit  30  is greater than the reference voltage Vref, the comparator  71  controls the control switch  73  to close, and the snubber circuit  50  is activated and works to protect the buck converter  10 . When the output voltage Vout of the peak detecting circuit  30  is less than the reference voltage Vref, the comparator  71  controls the control switch  73  to open, and the snubber circuit  50  is cut off and stops working to avoid power being consumed by the snubber circuit  50 . 
         [0022]    In the embodiment, the first input terminal  701  is a normal phase one and the second input terminal  702  is an abnormal phase one. The control switch  73  is a NMOS transistor. When the output voltage Vout of the peak detecting circuit  30  is greater than the reference voltage Vref, the buck converter  10  is under the heavy load, and the comparator  71  outputs a high level signal and controls the control switch  73  to close. When the output voltage Vout of the peak detecting circuit  30  is less than the reference voltage Vref, the buck converter  10  is under the light load, and the comparator  71  outputs a low level signal and controls the control switch  73  to open. 
         [0023]    The working process of the power control device  100  is described as below. The PSU  12  provides the input voltage Vin to the buck converter  10 , and then the controller  11  sends PWM signals to the first switch Q 1  and the second switch Q 2  to selectively close or open the first switch Q 1  and the second switch Q 2 . The peak detecting circuit  30  detects the voltage Vx, and the logic circuit  70  compares the voltage Vx with the reference voltage Vref. If the voltage Vx is greater than the reference voltage Vref, the buck converter  10  is deemed to be under the heavy load. The peak detecting circuit  30  triggers the comparator  71  to close the control switch  73 . Thus, the snubber circuit  50  is connected in parallel with the second switch Q 2  to decrease and protect against any voltage spike of the voltage Vx. If the voltage Vx is less than the reference voltage Vref, the buck converter  10  is deemed to be under the light load. The peak detecting circuit  30  triggers the comparator  71  to open the control switch  73  and thus disconnect the snubber circuit  50 . Thus, the snubber circuit  50  is disconnected from the second switch Q 2  and power loss is avoided. 
         [0024]    The peak detecting circuit  30  determines whether the buck converter  10  is under the heavy load or the light load. If the buck converter  10  is under the heavy load, the peak detecting circuit  30  triggers the comparator  71  to allow the snubber circuit  50  to connect in parallel with the second switch Q 2 , to decrease any voltage spike. If buck converter  10  is under the light load, the peak detecting circuit  30  triggers the comparator  71  to allow the snubber circuit  50  to be disconnected from the second switch Q 2  and the power drain represented by the snubber circuit  50  is avoided. 
         [0025]    It is to be understood, however, that even though numerous characteristics and advantages of the exemplary disclosure have been set forth in the foregoing description, together with details of the structure and function of the exemplary 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 exemplary disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.