Patent Publication Number: US-2013241521-A1

Title: Voltage stabilizing circuit and electronic device

Description:
BACKGROUND 
     1. Technical Field 
     The disclosed embodiments relate to a voltage stabilizing circuit and an electronic device. 
     2. Description of Related Art 
     A three terminal voltage regulator includes an input pin and an output pin. The input pin receives an external input voltage. The three terminal voltage regulator regulates the external input voltage to a stabilized supply voltage, and outputs the stabilized supply voltage through the output pin. However, sometimes, the external input voltage may be larger than a rated voltage of the three terminal voltage regulator, causing the three terminal voltage regulator to malfunction or be damaged. 
     One solution to the above problems, is to provide a three terminal voltage regulator having a higher rated voltage. However, the maximum rated power of the three terminal voltage regulator is limited, because the rated voltage of the three terminal voltage regulator is high, the output current of the updated three terminal voltage regulator may be too small to power the load. 
     Therefore, there is room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments 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. Moreover, in the drawings, like reference numerals designate corresponding parts throughout one views. 
       The FIGURE is a block diagram of an electronic device in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an electronic device  900  includes a power source  100 , a load  300 , and a voltage stabilizing circuit  200  connected between the power source  100  and the load  300 . The power source  100  outputs an external input voltage. 
     The voltage stabilizing circuit  200  includes an input terminal  202 , a voltage reduction unit  10 , and a three terminal voltage regulator  20 . The input terminal  202  receives the external input voltage from the power source  100 . The three terminal voltage regulator  20  includes an input pin  22 , a ground pin  24  and an output pin  26 , the ground pin  24  is grounded. The voltage reduction unit  10  receives the external input voltage from the input terminal  202 , reduces the external input voltage, and outputs the reduced external input voltage to the input pin  22 . In this embodiment, the reduced external input voltage is a stabilized value. 
     The three terminal voltage regulator  20  regulates the reduced external input voltage to a stabilized supply voltage, and outputs the stabilized supply voltage through the output pin  26  for powering the load  300 . In this embodiment, the external input voltage is larger than a rated voltage of the three terminal voltage regulator  20 . 
     In detail, the voltage reduction unit  10  includes a switch element  12 , a voltage stabilizing element  14 , and a current limiting element  16 . The switch element  12  includes a control terminal  120 , a first conducting terminal  122  connected to the input terminal  202 , and a second conducting terminal  124  connected to the input pin  22 . One end of the voltage stabilizing element  14  is connected to the control terminal  120 , the other end of the voltage stabilizing element  14  is grounded. One end of the current limiting element  16  is connected to the first conducting terminal  122 , the other end of the current limiting element  16  is connected to the control terminal  120 . 
     When the external input voltage is larger than a predetermined voltage, a first stabilizing voltage is generated across the voltage stabilizing element  14  and the switch element  12  is turned on to generate a second stabilizing voltage between the control terminal  120  and the second conducting terminal  124 . Therefore, the reduced external input voltage is equal to a subtraction of the second stabilizing voltage from the first stabilizing voltage and stability is maintained. 
     In this embodiment, the voltage stabilizing element  14  is a zener diode D 1 , an anode of the zener diode D 1  is grounded, a cathode of the zener diode D 1  is connected to the control terminal  120 ; the predetermined voltage is equal to a zener voltage of the zener diode D 1 , and the first stabilizing voltage is equal to the zener voltage. For example, when the external input voltage is larger than 15 volts, 15 volts is generated across the zener diode D 1 . 
     In this embodiment, the switch element  12  is a transistor Q 1 , a base of the transistor Q 1  is the control terminal  120 , a collector of the transistor Q 1  is the first conducting terminal  122 ; an emitter of the transistor Q 1  is the second conducting terminal  124 . The transistor Q 1  is a NPN type bipolar junction transistor. 
     In this embodiment, the current limiting element  16  is a resistor R 1 . 
     The voltage stabilizing circuit  200  further includes a first capacitor C 1  and a second capacitor C 2 . One end of the first capacitor C 1  is connected to the input pin  22 , the other end of the first capacitor C 1  is grounded. One end of the second capacitor C 2  is connected to the output pin  26 , the other end of the second capacitor C 2  is grounded. 
     In the voltage stabilizing circuit  200 , because the external input voltage is reduced by the voltage reduction unit  10  and the reduced external input voltage is supplied to the input pin of the three terminal voltage regulator  20 , the rated voltage of the three terminal voltage regulator  20  can be small; even if the maximum rated power of the three terminal voltage regulator  20  is limited, the output current of the three terminal voltage regulator  20  is still enough to power the load  300 . 
     Alternative embodiments will become apparent to those skilled in the art without departing from the spirit and scope of what is claimed. Accordingly, the present disclosure should not be deemed to be limited to the above detailed description, but rather only by the claims that follow and the equivalents thereof.