Abstract:
A voltage adapter characterized by an advantage of reducing unnecessary power loss induced in standby mode operation and conserving the overall power consumption accordingly. The voltage adapter according to the present invention receives an input voltage and converts the input voltage into an output voltage having a voltage level different from the input voltage, and comprises an EMI filter for suppressing a differential mode noise in the input voltage, a bridge rectifier for performing a full-wave rectification to the input voltage, a transistor switch, a driver for controlling on/off operations of the transistor switch according to a feedback amount derived from the output voltage, and a circuit box for providing a discharge path for the EMI filter, while sampling the input voltage to detect a variation of the input voltage.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a voltage adapter, and more particularly to a voltage adapter which is able to conserve power consumption under standby mode.  
       BACKGROUND OF THE INVENTION  
       [0002]     Generally speaking, a voltage adapter, more particularly an AC/DC adapter, is used to receive a commercially available alternating-current (AC) power and convert the AC power into a direct-current (DC) power in order to enable a DC/DC converter to transform a high-level DC voltage into various low-level DC voltages, and thereby operating an electronic device. The electronic device which is adapted to cooperate with a DC power source can be, for example, a desktop computer.  
         [0003]     The circuit configuration of a conventional AC/DC adapter is illustrated in  FIG. 1 . The AC/DC adapter as shown in  FIG. 1  includes an input AC power source Vin, an EMI (electromagnetic interference) filter  11 , a bridge rectifier  12 , an input power detecting circuit  13 , an energy storage device  14 , a transistor switch Q 1 , a driver  15 , and an output filter  16 . The EMI filter  11  is constituted by an input power filtering capacitor X-cap, which is used to suppress the differential mode noise in the input AC voltage Vin. The input power filtering capacitor X-cap is connected with three serially-connected discharge resistors Rx in parallel, and the discharge resistors Rx are used to provide a discharge path for the input power filtering capacitor X-cap of the EMI filter  11  to release the energy stored therein. The bridge rectifier  12  comprises a plurality of diodes, and is used to perform a full-wave rectification to the input AC voltage Vin. The AC voltage generated by the bridge rectifier  12  is converted to a DC voltage by a DC/AC converter (not shown). The energy storage device  14  is used to store energy while the transistor switch Q 1  is ON, and release the energy stored therein to the output filter  16  while the transistor switch Q 1  is OFF. The output filter  16  comprises a diode D 1  and a capacitor C 1 , and is used to perform a filtering and smoothing operation to the received DC voltage so as to provide an output DC voltage. The driver  15  is used to control on/off operations of the transistor switch Q 1  according to a feedback amount derived from the output DC voltage, and thereby stabilize the output DC voltage. In addition, the AC/DC adapter further includes an input power detecting circuit  13  for sampling the input AC voltage and detecting the variation of the input AC voltage accordingly. The variation of the input AC voltage detected by the input power detecting circuit  13  is provided to the driver  15 . Generally, the input power detecting circuit  13  comprises a voltage divider including a resistor R and a resistor r, whereas the resistance of the resistor r is far smaller than that of the resistor R.  
         [0004]     Most of the portable electronic devices today are provided with power management facilities, and are able to adjust the allocation of the available power in response to user&#39;s demands and build the parameters used in standby mode operation. Thus, the portable electronic devices today are more power-saving than ever before and are able to work for a prolonged period. When the whole system is working under a standby mode, most of the internal circuit elements of the voltage adapter, including the transistor switch Q 1  and the driver  15 , are all shut down and stop operating. However, some passive circuit elements of the voltage adapter, for example, the discharge resistors Rx and the resistors R and r located within the input power detecting circuit  13 , continue to receive the input AC voltage Vin and cause power consumption under standby mode. The senseless power consumption dissipated as a result of the passive circuit elements of the voltage adapter in standby mode operation will increase the overall power consumption of an electronic device.  
         [0005]     Therefore, a major target to be pursued by the present invention is focused on the reduction of the power consumption resulted from the passive circuit elements, especially the resistors of the voltage adapter in standby mode operation.  
       SUMMARY OF THE INVENTION  
       [0006]     A major object of the present invention is to provide a voltage adapter capable of conserving power consumption under standby mode.  
         [0007]     In a preferred embodiment of the present invention, there is provided a voltage adapter for attaining the object of the present invention. The voltage adapter is used to receive an input voltage and convert the input voltage into an output voltage having a voltage level different from the input voltage, and includes an electromagnetic interference filter for suppressing a differential mode noise of the input voltage, a bridge rectifier connected to the electromagnetic interference filter for performing a full-wave rectification to the input voltage, a transistor switch connected to the bridge rectifier, a driver connected to the transistor switch for controlling on/off operations of the transistor switch according to a feedback amount derived from the output voltage, and a circuit box connected to the electromagnetic interference filter, the bridge rectifier, and the driver for providing a discharge path to the electromagnetic interference filter while sampling the input voltage to detect a variation of the input voltage.  
         [0008]     Now the foregoing and other features and advantages of the present invention will be best understood through the following descriptions with reference to the accompanying drawings, wherein: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  shows the circuit diagram of a conventional AC/DC adapter;  
         [0010]     FIGS.  2 (A)- 2 (C) show the voltage waveform diagrams associated with the conventional AC/DC adapter of  FIG. 1 ;  
         [0011]      FIGS. 3, 4 ,  5  and  6  show the equivalent circuit diagrams of the conventional AC/DC adapter of  FIG. 1 ; and  
         [0012]      FIG. 7  shows the circuit diagram of the voltage adapter according to the preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     The predominant feature of the present invention is practiced by combining the resistors of the input power detecting circuit being used to detect the variation of the input voltage with the resistors forming the discharge path for the electromagnetic interference filter together, in such manner that the power consumption caused by the passive resistor elements of the voltage adapter is reduced under standby mode. Detailed descriptions of a preferred embodiment according to the present invention will be given as follows.  
         [0014]     FIGS.  2 (A)- 2 (C) show voltage waveform diagrams associated with the conventional AC/DC adapter of  FIG. 1 . In these diagrams,  FIG. 2 (A) shows the voltage waveform of the input AC voltage Vin,  FIG. 2 (B) shows the voltage waveform of the AC voltage derived from the input AC voltage Vin being full-wave rectified by a bridge rectifier  12 , and  FIG. 2 (C) shows the voltage waveform of the sampled input voltage detected by the input power detecting circuit  13  of  FIG. 1 . It can be clearly seen from  FIG. 2 (B) that the resulted AC voltage of the input AC voltage Vin being full-wave rectified has a similar phase with the input AC voltage Vin, but has an amplitude of a positive value, regardless of whether the input AC voltage Vin is going through its positive half cycle or its negative half cycle. In  FIG. 2 (C), the input power detecting circuit of  FIG. 1  uses a voltage divider comprising resistors R and r to sample the input AC voltage and detects the variation of the input AC voltage. Thus the amplitude of the sampled input voltage will be equal to  
         r     r   +   R       ⁢     Vin   .         
 
 The driver  15  shown in  FIG. 1  utilizes the sampled input voltage to adjust the power factor of the input voltage and thereby determine the operation voltage range of the input voltage. 
 
         [0015]      FIG. 7  depicts the circuit configuration of the voltage adapter according to a preferred embodiment of the present invention. Next, it is intended to elaborate on the transforming steps of deducing the circuit configuration of  FIG. 7  from the circuit configuration of  FIG. 1  with reference to the circuit configurations as shown in FIGS.  3  to  6 , such that those skilled in the art would be able to realize the spirits and principles contained in the present invention, and further concretize the circuit design norm carried out by the present invention based on the teachings suggested herein.  
         [0016]     Referring to  FIG. 3 , which is a first equivalent circuit configuration of the voltage adapter of  FIG. 1 . With reference to the circuit configuration of  FIG. 3 , the input current will flow through a first diode  22 , a resistor R connected between the EMI filter  11  and the first diode  22 , and a resistor r connected between the first diode  11 , a second diode  24  and the ground terminal during the positive half-cycle of the input AC voltage. During the positive half-cycle of the input AC voltage, the amplitude of the detected sampled input voltage will thus be  
           r     r   +   R       ⁢   Vin     ,       
 
 which is a positive value. Similarly, the input current will flow through the second diode  24 , a resistor R connected between the discharge resistor Rx and the second diode  24 , and the resistor r connected between the first diode  11 , the second diode  24  and the ground terminal during the negative half-cycle of the input AC voltage. During the negative half-cycle of the input AC voltage, the amplitude of the detected sampled input voltage will thus be  
           r     r   +   R       ⁢   Vin     ,       
 
 which is also a positive value. Therefore, according to the circuit configuration of  FIG. 3 , the voltage waveform of the sampled input voltage to be inputted to the driver  15  has the same profile with the voltage waveform of the sampled input voltage as shown in  FIG. 2 (C), and the circuit configuration of the voltage adapter as shown in  FIG. 3  can be considered an equivalent circuit of the voltage adapter of  FIG. 1 . 
 
         [0017]     Referring to  FIG. 4 , which is a second equivalent circuit configuration of the voltage adapter of  FIG. 1 . With reference to  FIG. 4 , the input current will flow through the first diode  22 , a resistor  1 / 2 R connected between the EMI filter  11  and the first diode  22 , a resistor  1 / 2 R connected between the first diode  22 , the second diode  24  and the driver  15 , and a resistor r connected between the driver  15  and the ground terminal during the positive half-cycle of the input AC voltage. Because the two resistors of  1 / 2 R,  1 / 2 R mentioned above are connected in series and thus their equivalent resistance is R, they can be considered an equivalence of the resistor R connected between the EMI filter  11  and the first diode  22  as shown in  FIG. 3 . Therefore, during the positive half-cycle of the input AC voltage, the amplitude of the detected sampled input voltage will still be  
           r     r   +   R       ⁢   Vin     ,       
 
 which is a positive value. Similarly, the input current will flow through the second diode  24 , a resistor  1 / 2 R connected between the discharge resistor Rx and the second diode  24 , the resistor  1 / 2 R connected between the second diode  24  and the driver  15 , and the resistor r connected between the driver  15  and the ground terminal during the negative half-cycle of the input AC voltage. Because the two resistors of  1 / 2 R,  1 / 2 R mentioned above are connected in series and thus their equivalent resistance is R, they can be considered an equivalence of the resistor R connected between the EMI filter  11  and the second diode  24  as shown in  FIG. 3 . Therefore, during the negative half-cycle of the input AC voltage, the amplitude of the detected sampled input voltage will thus be  
           r     r   +   R       ⁢   Vin     ,       
 
 which is also a positive value. In this way, according to the circuit configuration of  FIG. 4 , the voltage waveform of the sampled input voltage to be inputted to the driver  15  has the same profile with the voltage waveform of the sampled input voltage as shown in  FIG. 2 (C), and the circuit configuration of the voltage adapter as shown in  FIG. 4  can be considered an equivalent circuit of the voltage adapters of  FIGS. 1 and 3 . 
 
         [0018]     Referring to  FIG. 5 , which is a third equivalent circuit configuration of the voltage adapter of  FIG. 1 . With reference to the circuit configuration of  FIG. 5 , the two parallel-connected resistors R, R and the two parallel-connected resistors  2   r ,  2   r  will be combined in parallel to form an equivalent circuit comprising a resistor  1 / 2 R and a resistor r being connected in series. Therefore, the circuit configuration of  FIG. 5  can be considered an equivalent circuit of the circuit configuration of  FIG. 4 , and also an equivalent circuit of the circuit configurations of  FIGS. 1 and 3 .  
         [0019]     Referring to  FIG. 6 , which is a fourth equivalent circuit configuration of the voltage adapter of  FIG. 1 . With reference to the circuit configuration of  FIG. 6 , the input current will flow through the first diode  22  and the resistor  1 / 2 R connected between the upper terminal of the EMI filter  11  and the first diode  22 , and will divert to the resistors (R+ 2   r ) connected between the first diode  22 , the second diode  24  and the ground terminal, and the resistors ( 1 / 2 R+ 2   r + 1 / 2 R) connected between the first diode  22  and the lower terminal of the EMI filter  11  during the positive half-cycle of the input AC voltage. It is obvious that the resistance of the series combination comprising the resistors ( 1 / 2 R+ 2   r + 1 / 2 R) connected between the first diode  22  and the lower terminal of the EMI filter  11  is equivalent to the resistance of (R+ 2   r ), and thus the series combination comprising the resistors ( 1 / 2 R+ 2   r + 1 / 2 R) connected between the first diode  22  and the lower terminal of the EMI filter  11  can be considered one of the branch circuits of the parallel combination connected between the first diode  22 , the second diode  24  and the ground terminal as shown in  FIG. 5 . Hence, the circuit operation in the positive half-cycle of the input AC voltage according to the circuit configuration of  FIG. 6  undergoes the same situation with  FIG. 5 . During the negative half-cycle of the input AC voltage, the input current will flow through the second diode  24  and the resistor  1 / 2 R connected between the lower terminal of the EMI filter  11  and the second diode  24 , and will divert to the resistors (R+ 2   r ) connected between the first diode  22 , the second diode  24  and the ground terminal, and the resistors ( 1 / 2 R+ 2   r + 1 / 2 R) connected between the upper terminal of the EMI filter  11  and the second diode  24 . It is obvious that the resistance of the series combination comprising the resistors ( 1 / 2 R+ 2   r + 1 / 2 R) connected between the upper terminal of the EMI filter  11  and the second diode  24  is equivalent to the resistance of (R+ 2   r ), and thus the series combination comprising the resistors ( 1 / 2 R+ 2   r + 1 / 2 R) connected between the upper terminal of the EMI filter  11  and the second diode  24  can be considered one of the branch circuits of the parallel combination connected between the first diode  22 , the second diode  24  and the ground terminal as shown in  FIG. 5 . Hence, the circuit operation in the negative half-cycle of the input AC voltage according to the circuit configuration of  FIG. 6  undergoes the same situation with  FIG. 5 . In this manner, the circuit configuration of  FIG. 6  can be considered an equivalence to the voltage configurations of  FIG. 1 ,  FIG. 3 ,  FIG. 4 , and  FIG. 5 .  
         [0020]     Here we designate the resistor  1 / 2 R connected between the anode of the first diode  22  and the EMI filter  11  (input power filtering capacitor X-cap) as a first resistor, the resistor ( 1 / 2 R+ 2   r ) connected between the anode of the first diode  22  and the anode of the second diode  24  as a second resistor, the resistor  1 / 2 R connected between the anode of the second diode  24  and the EMI filter  11  (input power filtering capacitor X-cap) as a third resistor, the resistor R connected between the cathode of the first diode  22 , the cathode of the second diode  24 , and the driver  15  as a fourth resistor, and the resistor  2   r  connected between the driver  15  and the ground terminal as a fifth resistor.  
         [0021]     Next, because the function of the three serially-connected discharge resistors Rx as shown in the circuit configuration of  FIG. 6  is to provide a discharge path for the input power filtering capacitor X-cap only, the discharge capacitors Rx can be merged with the first resistor, the second resistor and the third resistor. That is, the discharge resistors Rx can be eliminated, and the circuit box comprising the first resistor, the second resistor and the third resistor can be used to replace the discharge resistors as the unit that provides a discharge path for the input power filtering capacitor X-cap. Moreover, because the component  1 / 2 R of the second resistor is far larger than the other component  2   r  of the second resistor, the resistance of the second resistor can be approximated to  1 / 2 R. Through the aforementioned steps to simplify the complexity of the circuit configuration of the voltage adapter, the circuit configuration of the voltage adapter according to a preferred embodiment of the present invention can be concluded in the circuit diagram of  FIG. 7 .  
         [0022]     The above description has fully illustrated the procedural steps of how to attain the circuit configuration of the voltage adapter according to the present invention through the evolvement with a series of equivalent circuits obtained by modifying the circuit configuration of the conventional voltage adapter with the replacement and integration of its circuit elements. It can be understood from the circuit diagram of  FIG. 7  that the voltage adapter of the present invention provides an advantage that reduces the power consumption under standby mode resulted from the power loss caused by the passive resistor elements. This is done by placing a circuit box in the voltage adapter of the present invention that provides a discharge path for the EMI filter while detecting the variation of the input voltage by processing the input voltage with a sampling operation. In a detailed aspect of the present invention, the constitution of the circuit box includes a first resistor  1 / 2 R having a first terminal connected to the EMI filter  11  and a second terminal; a second resistor  1 / 2 R having a first terminal connected to the second terminal of the first resistor and a second terminal; a third resistor  1 / 2 R having a first terminal connected to the second terminal of the second resistor and a second terminal connected to the EMI filter  11 ; a first diode  22  having a first terminal connected commonly to the first terminal of second resistor and the second terminal of the first resistor, and a second terminal; a second diode  24  having a first terminal connected commonly to the first terminal of third resistor and the second terminal of the second resistor, and a second terminal; a fourth resistor R having a first terminal connected commonly to the second terminal of the first diode  22  and the second terminal of the second diode  24 , and a second terminal connected to the driver  15 ; and a fifth resistor  2   r  having a first terminal connected to the second terminal of the fourth resistor, and a second terminal connected to the ground terminal. Compared to the conventional voltage adapter of  FIG. 1 , the power loss induced in standby mode operation within the voltage adapter of the present invention is equal to  
           Vin   2           1   2     ⁢   R     +       1   2     ⁢   R     +   r       ,       
 
 while the power loss induced in standby mode operation within the conventional voltage adapter of  FIG. 1  is equal to  
           Vin   2       3   ⁢   Rx       +         Vin   2       R   +   r       .         
 
 According to the present invention, the resistance of the resistors ( 1 / 2 R+ 1 / 2 R+r) should be equivalent to  3 Rx, and thereby the voltage adapter of the present invention can reduce the standby mode power consumption by an amount up to  
           Vin   2       R   +   r       .       
 
 Therefore, the present invention is competent to substantially reduce the power loss induced in the standby mode operation from the passive resistor elements, and further conserve the overall power consumption. 
 
         [0023]     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.