Patent Publication Number: US-2013241295-A1

Title: Power management circuit and electronic device

Description:
BACKGROUND 
     1. Technical Field 
     The disclosed embodiments relate to a power management circuit and an electronic device. 
     2. Description of Related Art 
     The power management circuit is widely used in electronic devices. The power management circuit is connected between a power source and a load, the power management circuit receives a supply voltage from the power source and provides an operation voltage to the load in response to an external control signal. The power management circuit has a feedback terminal, a sampling circuit samples the operation voltage to generate a sampling voltage and outputs the sampling voltage to the feedback terminal. The power management circuit adjusts the operation voltage according to the sampling voltage. 
     However, the adjustment of the power management circuit is limited, when the supply voltage is suddenly reduced, the operation voltage is also reduced. Therefore, the reduced operation voltage may not be enough 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 two views. 
         FIG. 1  is a block diagram of an electronic device in accordance with one embodiment. 
         FIG. 2  is a circuit diagram of the electronic device of  FIG. 1  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 power management circuit  200  connected between the power source  100  and the load  300 . The power source  100  includes a first power supply  10 , a second power supply  12  (see  FIG. 2 ), a first power terminal  101 , and a second power terminal  102 . The first power supply  10  outputs a first supply voltage through the first power terminal  101 , the second power supply  12  outputs a second supply voltage through the second power terminal  102 . When the first power terminal  101  outputs the first supply voltage, the second power terminal  102  stops outputting the second supply voltage; when the second power terminal  102  outputs the second supply voltage, the first power terminal  101  stops outputting the first supply voltage. 
     Firstly, we describe a first situation when the first power terminal  101  outputs the first supply voltage and the second power terminal  102  stops outputting the second supply voltage. The power management circuit  200  includes a first switch unit  22 , a pulse width modulation (PWM) unit  24  having an input power terminal  240  and an output terminal  242 , a storage unit  25 , and a first sampling unit  26 . The first switch unit  22  is capable of being turned on to establish a first electrical connection between the first power terminal  101  and the input power terminal  240  or being turned off to cut off the first electrical connection. In this embodiment, the first switch unit  22  is turned on or turned off in response to an external control signal. 
     The input power terminal  240  receives the first supply voltage from the first power terminal  101  when the first switch unit  22  is turned on, thus the pulse width modulation unit  24  is powered by the first supply voltage to generate a pulse voltage at the output terminal  242 . The storage unit  25  is connected between the input power terminal  240  and the output terminal  242 . The storage unit  25  receives the first supply voltage to store energy when the pulse voltage is in a first level, and releases energy to generate an operating voltage at the output terminal  242  when the pulse voltage is in a second level; the operating voltage powers the load  300 . 
     In this embodiment, the first level is a low level, the second level is a high level; furthermore, when the pulse voltage is in the first level, the pulse voltage is zero volts, when the pulse voltage is in the second level, the pulse voltage is equal to the first supply voltage and the operating voltage is equal to two times the first supply voltage. 
     The first sampling unit  26  samples the operating voltage to generate a sampling voltage, the pulse width modulation unit  24  adjusts a duty cycle of the pulse voltage according to the sampling voltage. In detail, when the sampling voltage is larger than a threshold voltage, the pulse width modulation unit  24  decreases the duty cycle; when the sampling voltage is smaller than the threshold voltage, the pulse width modulation unit  24  increases the duty cycle. Therefore, the operating voltage keeps stable. 
     Secondly, we describe a second situation when the second power terminal  102  outputs the second supply voltage, the first power terminal  101  stops outputting the first supply voltage. The power management circuit  200  further includes a second switch unit  28 , a voltage reduction unit  30 , and a second sampling unit  32 . 
     The second switch unit  28  is connected between the second power terminal  102  and the voltage reduction unit  30 . The second switch unit  28  is capable of being turned on to establish a second electrical connection between the second power terminal  102  and the voltage reduction unit  30  or being turned off to cut off the second electrical connection. In this embodiment, the first switch unit  22  and second switch unit  28  are simultaneously turned on or turned off in response to the external control signal. 
     The voltage reduction unit  30  receives the second supply voltage from the second power terminal  102  through the second switch unit  28  when the second switch unit  28  is turned on, reduces the second supply voltage, and provides the reduced second supply voltage to the input power terminal  240  of the pulse width modulation unit  24  through the first switch unit  22  when the first switch unit  22  is turned on. The pulse width modulation unit  24  is powered by the reduced second supply voltage to generate the pulse voltage at the output terminal  242 . Therefore, the storage unit  25  receives the reduced second supply voltage to store energy when the pulse voltage is in the first level, and releases energy to generate the operating voltage at the output terminal  242  when the pulse voltage is in the second level. 
     Second sampling unit  32  samples the reduced second supply voltage to generate a sampling signal, the voltage reduction unit  30  adjusts the reduced second supply voltage according to the sampling signal, therefore keeping the reduced second supply voltage stable. 
     Referring to  FIG. 2 , the power management unit  200  further includes a second diode D 2 . The power source  100  comprises a first power supply  10  for outputting the first supply voltage, a second power supply  12  outputting the second supply voltage, a transistor Q 1  and a first diode D 1 . The gate of the transistor Q 1  is connected to the second power supply  12 , the drain of the transistor Q 1  is connected to the first power supply  10 , the source of the transistor Q 1  is connected to a cathode of the second diode D 2  and the first switch unit  22 , and an anode of the second diode D 2  is connected to the voltage reduction unit  30 . An anode of the first diode D 1  is connected to the drain of the transistor Q 1 , a cathode of the first diode D 1  is connected to the source of the transistor Q 1 . 
     The source of the transistor Q 1  receives the reduced second supply voltage from the voltage reduction unit  30  when the second switch unit  28  is turned on, the reduced second supply voltage is larger than the first supply voltage, thus the transistor Q 1  is turned off and the first diode D 1  is reverse-biased; therefore, the first power terminal  101  stops outputting the first supply voltage and the second power terminal  102  outputs the second supply voltage. When the second power supply  12  stops outputting the second supply voltage, the transistor Q 1  is turned on and the first diode D 1  is forward-biased, therefore the first power terminal  101  outputs the first supply voltage and the second power terminal  102  stops outputting the second supply voltage. 
     In this embodiment, the first power supply  10  is a battery, the second power supply  12  is an adaptor for converting an AC voltage (for example, 220 volts) to a DC voltage, the DC voltage is equal to the second supply voltage. 
     The storage unit  25  comprises an inductor L 1 , one end of the inductor L 1  is connected to the input power terminal  240 , and the other end of the inductor L 1  is connected to the output terminal  242 . In other embodiments, the storage unit  25  comprises a capacitor, one end of the capacitor is connected to the input power terminal  240 , and the other end of the capacitor is connected to the output terminal  242 . 
     In the electronic device  900 , when the first supply voltage or the second supply voltage is suddenly increased, because the storage unit  25  stores energy when the pulse voltage is in the low level and release energy when the pulse voltage is in the high level, the operation voltage will still 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.