Patent Publication Number: US-2010124078-A1

Title: Electronic device and power supply thereof

Description:
BACKGROUND 
     1. Technical Field 
     Embodiments of the present disclosure relate to power supplies, and particularly to a power supply of an electronic device. 
     2. Description of Related Art 
     Power supplies, having multiple outputs, usually adopts a tapped transformer and a convertor to convert a voltage from the mains/wall power to two or more lower direct current (DC) voltages. The two or more DC voltages are used to power different operation modules of an electronic device, such as a television, a desktop computer, a notebook computer, a projector, etc. Most current transformers need five taps (as used here, a tap refers to any connection to the secondary coil of the transformer) for two outputs. This tap to output ratio complicates the design of the power supply, has poor utilization of the transformer winding, and produces an excessive amount of electro-magnetic interferences (EMI). 
     Therefore, an improved power supply for an electronic device is needed to address the aforementioned deficiency and inadequacies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with references 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 embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a block diagram showing an electronic device including a power supply in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a circuit diagram showing the power supply of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an electronic device  800  in accordance with an exemplary embodiment includes a power supply  100  and a plurality of operation modules  300 . The electronic device  800  may be a desktop computer, a television, a projector, a media player, etc. The plurality of operation modules  300  may include a display, an input device, an audio output module, a data processing unit, etc. The power supply  100  is configured for supplying the appropriate direct current (DC) voltages to the plurality of operation modules  300 . In the embodiment, the power supply  100  is a switched mode power supply (SMPS). 
     The power supply  100  includes a first convertor  10 , a second convertor  30 , and a transformer  20  electrically connected between the first and second convertors  10 ,  30 . The power supply  100  is capable of utilizing three taps of the transformer winding to supply two outputs, thus producing less electro-magnetic interferences (EMI). 
     Referring to  FIG. 2 , the first convertor  10  is configured for supplying an alternating current (AC) voltage. The transformer  20  generates an inducted voltage based on the AC voltage. The transformer  20  includes a primary winding and a secondary winding. The primary winding is connected to the first convertor  10  via two terminals T 1 , T 2 , and receives the AC voltage. The secondary winding includes a first tap T 3 , a second tap T 4 , and a third tap T 5  disposed between the first tap T 3  and the second tap T 4 . The third tap T 5  is the center tap of the secondary winding. 
     In the embodiment, the first convertor  10  includes an AC/DC convertor  101 , a controller  103 , a first switch component Q 1 , a second switch component Q 2 , and a third capacitor C 3 . The AC/DC convertor receives an AC voltage from the wall power via a plug (not shown), and converts the AC voltage into a third DC voltage and a fourth DC voltage. The third DC voltage is supplied to the first switch component Q 1 , and the fourth DC voltage is supplied to and powers the controller  103 . 
     The controller  103  is configured to alternately turn on and turn off the first switch component Q 1  and second switch component Q 2 . When the first switch component Q 1  is turned on, the second switch component Q 2  is turned off. 
     The first switch component Q 1  receives the third DC voltage and transmits it to the primary winding of the transformer  20  to charge the third capacitor C 3  when the first switch component Q 1  is turned on. The second switch component Q 2  grounds the primary winding of the transformer  20  when the second switch component Q 2  is turned on, and the third capacitor C 3  discharges via the primary winding and the second switch component Q 2 . In the embodiment, the first switch component Q 1  and the second switch component Q 2  are both metal-oxide semiconductor field-effect transistors (MOSFET). The drain of the first switch component Q 1  receives the third DC voltage, the gate of the first switch component Q 1  is connected to the controller  103 , and the source of the first switch component Q 1  is connected to the terminal T 1  of the primary winding and the drain of the second switch component Q 2 . The gate of the second switch component Q 2  is connected to the controller  103 , and the source of the second switch component Q 2  is grounded. In other embodiments, the first switch component Q 1  and the second switch component Q 2  may be bipolar junction transistors (BJT). 
     The second convertor  30  includes a first rectifier circuit  30   a  and a second rectifier circuit  30   b . The first rectifier circuit  30   a  is connected to the first tap T 3  and the second tap T 4 , converts the induced voltage into a first DC voltage, and outputs the first DC voltage via a first output terminal Vo 1 . The second rectifier circuit  30   b  is connected to the third tap T 5 , converts a half of the induced voltage into a second DC voltage, and outputs the second DC voltage via a second output terminal Vo 2 . Understandably, because of the center tap, the first DC voltage is double the second DC voltage. 
     In the embodiment, the first rectifier circuit  30   a  includes a diode bridge D, a first capacitor C 1 , and a first inductor L 1 . The diode bridge D includes two input terminals connected to the first and second taps T 3 , T 4  of the secondary winding of the transformer  20 , a ground terminal, and an output terminal connected to a terminal of the first capacitor C 1  and a first terminal of the first inductor L 1 . The other terminal of the first capacitor C 2  is grounded. A second terminal of the first inductor L 1  is connected to the first output terminal Vo 1 . The second rectifier circuit  30   b  includes a second capacitor C 2  and a second inductor L 2 . The second capacitor C 2  includes a first terminal connected to the third tap T 5  of the transformer  20 , and a second terminal connected to ground. The second inductor L 2  includes a first terminal connected to the third tap T 5 , and a second terminal connected to the second output terminal Vo 2 . 
     To summarize, the power supply  100  utilizes three taps of the transformer  20  to generate two different DC voltages. The structure of the circuit of the power supply  100  is simpler, and produces less EMI. Furthermore, the transformer can use a wide secondary winding, thus reducing power loss. 
     In other embodiments, when two more DC voltage is needed, another secondary winding similar to the above-described secondary winding and another convertor similar to the second convertor  30  can be utilized. When only one more DC voltage is needed, another secondary winding including two outer taps and a rectifier circuit similar to the first rectifier circuit  30   a  can be utilized. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, 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 disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.