Patent Publication Number: US-2013241517-A1

Title: Power circuit having three-terminal regulator

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to power circuits and, particularly, to a power circuit having a three-terminal regulator capable of increasing power output efficiency. 
     2. Description of the Related Art 
     A power circuit employed in an electronic device may include a three-terminal regulator for converting a higher voltage to a lower voltage, which results in a low efficiency and a high heat loss or consumption. Referring to  FIG. 1 , a power circuit  10  of related art includes an integrated three-terminal regulator  11 . The integrated three-terminal regulator  11  includes an input port  110 , a first output port  111 , and a second output port  112 . The input port  110  is connected to a power supply (not shown). The first output port  111  and the second output port  112  are connected to a power output port  12  of the power circuit  10 . The integrated three-terminal regulator  11  converts the voltage provided by the power supply into a predetermined voltage and outputs the converted voltage. For example, if the voltage provided by the power supply is 12V, and the predetermined voltage is 3.3V, a power supply transition efficiency of the circuit  10  is P=Vout/Vin=3.3V/12V=27.5%, and power lost as heat in the circuit  10  is Pd=(Vin−Vout)*Iout=(12V−3.3V)*I. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a circuit diagram of a power circuit of related art having a three-terminal regulator. 
         FIG. 2  is a block diagram of a power circuit having a three-terminal regulator in accordance with an exemplary embodiment. 
         FIG. 3  is a circuit diagram of the power circuit of  FIG. 2  in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 2-3 , a power circuit  20  employed in a power supply device powers an electronic device connected to the power circuit  20 . The power circuit  20  includes a power input port  21 , a power output port  22 , a three-terminal regulator  23 , a voltage regulating circuit  24 , and a charge/discharge circuit  25 . The three-terminal regulator  23  includes an input port  230 , a first output port  231 , and a second output port  232 . The first output port  231  is connected to the second output port  232  to form a regulator output port  233  of the three-terminal regulator  23 . The voltage regulating circuit  24  includes a first terminal  240 , a second terminal  241 , a third terminal  242 , and a fourth terminal  243 . The first terminal  240  is connected to the power input port  21 . The second terminal  241  is connected to the input port  230  of the three-terminal regulator  23 . The third terminal  242  is connected to the power output port  22 . The fourth terminal  243  is grounded. The charge/discharge circuit  25  and the regulator output port  233  of the three-terminal regulator  23  are both connected to the power output port  22 . 
     In the embodiment, the three-terminal regulator  23  is capable of detecting a voltage value at the regulator output port  233  and enabling or disabling the input port  230  depending on the detected voltage value. If the three-terminal regulator  23  determines the detected voltage value is less than a predetermined voltage value, the three-terminal regulator  23  enables the input port  230  to receive voltage signals output by the voltage regulating circuit  24 . If the three-terminal regulator  23  determines the detected voltage value is equal to or greater than the predetermined value, the three-terminal regulator  23  disables the input port  230 . In the embodiment, the predetermined voltage value is 3.3V. 
     In the embodiment, the voltage regulating circuit  24  includes a transformer T and a diode D. The transformer T includes a primary coil T 1  and a secondary coil T 2 . The primary coil T 1  is connected between the power input port  21  and the input port  230  of the three-terminal regulator  23 . A first terminal of the secondary coil T 2  is connected to the power output port  22 , a second terminal of the secondary coil T 2  is grounded via the diode D which is connected in reverse. The charge/discharge circuit  25  includes a capacitor C. A first terminal of the capacitor C is connected to the power output port  22  and a second terminal is grounded. 
     When a power supply (not shown) is connected to the power input port  21  for powering an electronic device (not shown) connected to the power output port  22 , the voltage value of the power input port  21  is equal to the voltage value of the power supply, and the voltage value of the power output port  22  is zero. Thereby, the voltage value of the regulator output port  233  of the three-terminal regulator  23  is equal to that of the power output port  22 , namely zero, and the three-terminal regulator  23  determines that the voltage value of the regulator output port  233  is lower than the predetermined value and so enables the input port  230 . The electric current provided by the power supply flows into the voltage regulating circuit  24  to drive the primary coil T 1  to generate induction. The secondary coil T 2  generates voltage according to the generated induction. Then the current flowing through the primary coil T 1  is also provided to the three-terminal regulator  23  to charge the capacitor C of the charge/discharge circuit  25 . Therefore, a portion of the power provided by the power supply is conducted to secondary coil T 2 , and another portion of the power provided by the power supply is conducted to the three-terminal regulator C to charge the charge/discharge circuit  25 . 
     The voltage value of the power output port  22  increases following the increase of the voltage across the capacitor C of the charge/discharge circuit  25 . When the voltage value of power output port  22  is equal to or greater than the predetermined voltage value, the three-terminal regulator  23  disables the input port  230 , thereby the current provided by the power supply flows only to the primary coil T 1  and the secondary coil T 2  generates a voltage accordingly. Then the voltage generated by the secondary coil T 2  and the voltage provided by the capacitor C are used for powering the electronic device connected to the power output port  22 . 
     The power supply transition efficiency is computed by a formula: P′=(Vout 1 +Vout 2 )Vin=(Vout 1 ++Vout 2 )/U, wherein Vout 1  is the voltage value of the secondary coil T 2 , Vout 2  is the voltage value of the capacitor C of the charge/discharge circuit  25 , namely 3.3V, and U is the voltage value of the power supply  20 . If the voltage value provided by the power supply is 12V, the power supply transition efficiency can be easily determined. 
     The power converted to heat and thus lost is computed by a formula: Pd′=(Vin*P′−Vout 2 )*I=(U*P′−Vout 2 )*I, wherein, the I is the current output by the secondary coil T 2  and the capacitor C of the voltage regulating circuit  24 . If the current output by the secondary coil T 2  and the capacitor C of the voltage regulating circuit  24  is 0.5 A, the heat consumption efficiency can be easily determined. 
     Therefore, the power supply transition efficiency P′ of the power circuit  20  of the present embodiment is greater than the power supply transition efficiency P of the power circuit  20  of related art, and the consumption or loss Pd′ of the power circuit  20  of the present embodiment is less than the consumption Pd of the power circuit  10  of the related art. 
     The voltage value of the capacitor C of the voltage regulating circuit  25  reduces when power to the electronic device is continued, and the voltage value of the power output port  22  is reduced accordingly. When the voltage value of the power output port  22  is less than the predetermined voltage, the three-terminal regulator  23  enables the input port  230 . The current provided by the power supply once again charges the capacitor C of the charge/discharge circuit  25 . 
     It is understood that the present disclosure may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein.