Abstract:
A power supply apparatus is provided. When an electronic apparatus coupled to the power supply is in standby mode, a microprocessor delivers a standby control pulse. A feedback circuit receiving the standby control pulse directs a pulse width modulation (PWM) controller to deliver a periodic intermittent signal. A switching device of the power supply apparatus reduces its switching action to reduce switching power lost upon receipt of activated periodic intermittent signal.

Description:
BACKGROUND  
       [0001]     The invention relates to a power supply apparatus, and more particularly, to a switching power supply apparatus able to reduce standby switching power loss when an electronic device is in standby mode.  
         [0002]     For improved transfer efficiency, a switching power supply transferring input power to power an electronic device according to a high frequency pulse-width-modulation (PWM) switching signal is often used. However, when the electronic device is in standby mode, power provided by the power supply apparatus is reduced and only power sufficient to keep the standby power saving control circuit working is provided to reduce power consumption.  
         [0003]      FIG. 1  is a block diagram of a conventional switching power supply apparatus. A power supply apparatus  1  comprises a rectifier  120 , PWM controller  121 , power transformer  122 , switching device  123 , and a feedback circuit  124 .  
         [0004]     When the power supply apparatus  1  detects the electronic device  130  is in standby mode, a standby control circuit in the PWM control circuit  121  controls a switching pulse which then reduces the frequency of a switching signal directly. Another method uses a burst, the frequency of the switching signal is not changed, but the PWM control circuit  121  stops the output of the switching pulse when in power saving, and re-starts the output of the switching pulse to provide power to the electronic device  130  when the power provided is lower than a predetermined limit.  
         [0005]     Therefore, when the electronic device  130  is in standby mode, the conventional power supply apparatus  1  provides not only supply power to the microprocessor of the electronic device  130  required for recovery from standby mode, but also powers the standby control circuit in PWM control circuit  121  to enable PWM control circuit  121  the output of switching signal in standby mode.  
         [0006]     However, the power provided to an electronic device is sometimes limited. For example, a portable computer receives power from attached batteries. To extend the battery time of the portable computer, the power consumption of components in the portable computer should be as low as possible. Power used by the standby control circuit when the electronic device is in standby mode creates power losses.  
       SUMMARY  
       [0007]     The invention provides a power supply apparatus for an electronic device comprising a microprocessor receiving a standby signal and outputting a standby controlling pulse. The power supply apparatus comprises a feedback circuit, a pulse width modulation (PWM) controller, a switching device, and a power transformer. The feedback circuit outputs a first controlling signal when not receiving the standby controlling pulse, and a second controlling signal when receiving the standby controlling pulse. The PWM controller is coupled to an output of the feedback circuit and outputs an intermittent signal continuously when receiving the first controlling signal, and periodically when receiving the second controlling signal. The switching device receives the intermittent signal and outputs a switching control signal by turning ON and OFF according to the high and low levels of the intermittent signal. The power transformer receives the switching control signal, and converts an input power to an output power according to the switching control signal.  
         [0008]     The invention also provides an electronic device comprising a circuit outputting a standby signal when in standby mode, a microprocessor receiving the standby signal and outputting a standby controlling pulse, and a power supply apparatus providing power for the electronic device. The power supply apparatus comprises a feedback circuit, a pulse width modulation (PWM) controller, a switching device, and a power transformer. The feedback circuit outputs a first controlling signal when not receiving the standby controlling pulse, and a second controlling signal when receiving the standby controlling pulse. The PWM controller is coupled to an output of the feedback circuit and outputs an intermittent signal continuously when receiving the first controlling signal, and periodically when receiving the second controlling signal. The switching device receives the intermittent signal and outputs a switching control signal by turning ON and OFF according to the high and low levels of the intermittent signal. The power transformer receives the switching control signal, and converts an input power to an output power according to the switching control signal.  
         [0009]     The invention further provides a method to provide power to an electronic device receiving a standby signal and outputting a standby controlling pulse. An intermittent signal is outputted continuously when not receiving the standby controlling pulse, and periodically when receiving the standby controlling pulse; a switching control signal is generated according to the intermittent signal. An output power is outputted according to the switching control signal.  
         [0010]     Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The features and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.  
         [0011]     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0012]     The accompanying drawings, incorporated in and constituting a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the features, advantages, and principles of the invention.  
         [0013]      FIG. 1  is a block diagram of a conventional switching power supply apparatus.  
         [0014]      FIG. 2  is a block diagram of a power supply apparatus consistent with a first embodiment of the invention.  
         [0015]      FIG. 3A  is a circuit schematic of power supply apparatus  2  consistent with the first embodiment of the invention.  
         [0016]      FIG. 3B  is a circuit schematic of an electronic device connected to the circuit shown in  FIG. 3A .  
         [0017]      FIG. 4A  shows an output waveform of the PWM controller during normal operation.  
         [0018]      FIG. 4B  shows the standby controlling pulse of the microprocessor.  
         [0019]      FIG. 4C  shows an output waveform of the PWM controller during standby mode.  
         [0020]      FIG. 5  shows a block diagram of an electronic device implementing a power supply apparatus consistent with the invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Consistent with the invention, a power supply apparatus is provided such that the PWM control circuit is controlled by the microprocessor when the electronic device is in standby mode, reducing the power used in standby mode.  
         [0022]      FIG. 2  is a block diagram of a power supply apparatus consistent with a first embodiment of the invention. When an electronic device  230  coupled to a power supply apparatus  2  is in standby mode, a circuit  250  outputs a standby signal SA directing the microprocessor  240  to output a standby controlling pulse S B .  
         [0023]     A switching device  223  receives switching signal S D , then executes ON and OFF operation accordingly to output a switching control signal S E . A power transformer  222  receives the switching control signal S E  and converts input power V DC  to output power according to the switching control signal S E . A rectifier  220  is coupled to an AC power and provides the input power VDC. A feedback circuit  224  is coupled to a power transformer  222  and an output terminal of the microprocessor  240 . The feedback circuit  224  outputs a first controlling signal when not receiving the standby controlling pulse S B , and outputs a second controlling signal when receiving the standby controlling pulse S B . The first controlling signal and the second controlling signal are transferred via the feedback signal S C  line. The PWM controller  221  is coupled to receive the feedback signal S C  and outputs an output signal S D  accordingly. The PWM controller  221  outputs a intermittent signal continuously when receiving the first controlling signal, and outputs the intermittent signal periodically when receiving the second controlling signal. Thus, the switching device  223  directs the power transformer  222  to output a standby power to maintain the minimum power of the microprocessor  240  according to the output signal S D  of the PWM controller  221 .  
         [0024]      FIG. 3A  is a circuit schematic of the power supply apparatus  2  consistent with the first embodiment of the invention.  FIG. 3B  is a circuit schematic of an electronic device connected to the circuit shown in  FIG. 3A . Power transformer  222  comprises a first coil N 1  receiving a DC power V DC  provided by the rectifier  220 , a second coil N 2  providing power for circuit  250 , a third coil N 3  providing power for the PWM controller  221 ; and a fourth coil N 4  providing power for the microprocessor  240 . Each of the second coil N 2 , the third coil N 3  and the fourth coil N 4  can have a rectifier  320  to provide stable power.  
         [0025]     When electronic device  230  is under normal operation, the feedback circuit  224  controls the duty-cycle of the output signal S D  of the PWM controller  221  according to a feedback of the power output. The switching device  223  adjusts the output power of the power transformer  222  according to the output signal S D .  
         [0026]     When the electronic device  230  is in standby mode, the circuit  250  outputs a standby signal S A  directing the microprocessor  240  to output the standby controlling pulse S B  and cut the power supply circuit between the power and the circuit  250 . When a high standby controlling pulse S B  is received by the feedback circuit  224 , the shunt regulator S 1  is ON′ driving optical coupler  225  to output a high signal. When a low standby controlling pulse S B  is received, the shunt regulator S 1  is OFF and driving optical coupler  225  to output a low signal.  
         [0027]     Thus, when the feedback circuit receives the standby controlling pulse S B , the second controlling signal is sent to direct the PWM controller  221  to output a intermittent signal periodically. In this embodiment, the PWM controller is a PWM controller IC and the switching device  223  is a MOSFET.  
         [0028]      FIGS. 4A-4C  show the control waveform of the power apparatus consistent with the first embodiment of the invention.  FIG. 4A  is the output waveform of the PWM controller under normal operation.  FIG. 4B  is the standby controlling pulse of the microprocessor.  FIG. 4C  is the output waveform of the PWM controller in standby mode.  
         [0029]      FIG. 4A  shows output waveform of the PWM controller under normal operation to be a continuous intermittent signal. When the electronic device  230  is in standby mode, the microprocessor outputs the standby controlling pulse as shown in  FIG. 4B . The feedback circuit then directs the PWM controller  221  to output a periodic intermittent signal according to the standby controlling pulse, as shown in  FIG. 4C .  
         [0030]     In addition, the power supply consistent with the invention is suitable for application in electronic devices, as shown in  FIG. 5 , to save power consumption in standby mode.  
         [0031]     The electronic device  500  shown in  FIG. 5  comprises a circuit  250 , a microprocessor  240  and a power supply apparatus  2 . For example, the electronic device  500  can be a LCD device while the circuit  250  is a LCD panel. The relationship between the power supply apparatus  2 , the circuit  250  and the microprocessor  240  is the same as described and therefore is not repeated.  
         [0032]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. Those who are skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.