Patent Publication Number: US-2013249318-A1

Title: Electronic device

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to electronic devices, and particularly relates to an electronic device with an internal battery. 
     2. Description of Related Art 
     Electronic device, such as DVD player, includes a battery, a processor, and a voltage sampling circuit. The battery provides a voltage for powering the processor. The voltage sampling circuit samples the voltage of the battery and includes a resistor connected between the battery and ground. The processor monitors the voltage of the battery according to the sampled voltage. The resistor forms a discharging path from the battery to ground. However, the resistor always dissipates the voltage of the battery even when the electronic device is powered off, and the battery will be discharged too quickly. 
     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 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 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIG. 1 , an electronic device  100  includes a power supply  10 , a voltage converting unit  20 , a processor  30 , a switching unit  40 , and a voltage sampling circuit  50 . The electronic device  100  can be powered on or powered off by the user, for example, in response to a power on command or a power off command from a remote controller. Furthermore, the electronic device  100  can receive other commands from the remote controller, and execute corresponding functions, for example, music playing function, and video playing function. In the embodiment, the electronic device  100  is a portable DVD player with an internal battery. 
     The power supply  10  provides a voltage to the voltage converting unit  20  and the switching unit  40 . In the embodiment, the power supply  10  is a battery, and the voltage is 7.4V. 
     The voltage converting unit  20  converts the voltage of the power supply  10  to a working voltage and outputs the working voltage to drive the processor  30 . In the embodiment, the working voltage is 3.3V. 
     The processor  30  generates a first control signal when the electronic device  100  is powered off, and generates a second control signal when the electronic device  100  is powered on. In the embodiment, the processor  30  is a micro control unit (MCU); the first control signal is a logic high voltage level, and the second control signal is a logic low voltage level. 
     The switching unit  40  is connected between the power supply  10  and the voltage sampling circuit  50 . The switching unit  40  cuts off the electrical connection between the power supply  10  and the voltage sampling circuit  50  in response to the first control signal, therefore, the switching unit  40  forms a first discharging path for discharging the power supply  10 . The switching unit  40  further establishes an electrical connection between the power supply  10  and the voltage sampling circuit  50  in response to the second control signal, therefore the voltage sampling circuit  50  forms a second discharging path for discharging the power supply  10  through the switching unit  40 , and the first discharging path is cut off. In this embodiment, the power consumption of the voltage sampling circuit  50  is greater than the power consumption of the switching unit  40 . Therefore, when the electronic device  100  is powered off, because the second discharge path is cut off excessive discharge of the power supply  10  is effectively prevented. 
     The voltage sampling circuit  50  samples the voltage of the power supply  10  when the electrical connection between the power supply  10  and the voltage sampling circuit  50  is established and outputs a sampled voltage to the processor  20 . The processor  20  further monitors the voltage of the power supply  10  based on the sampled voltage. In the embodiment, the processor  20  determines whether the voltage of the power supply  10  is lower than a predetermined voltage according to the sampled voltage; the processor  20  performs a power off procedure to cause the electronic device  100  to be powered off when the processor  20  determines that the voltage of the power supply  10  is lower than the predetermined voltage. 
     Referring to  FIG. 2 , the power supply  10  includes a power terminal V 1 . The power terminal V 1  provides voltage to the processor  30  and the switching unit  40 . 
     The processor  30  includes a MCU chip  31 . The MCU chip  31  includes a first pin P 1 , a second pin P 2 , and a third pin P 3 . The first pin P 1  is electronically connected to the voltage converting module  20 , and is used for receiving the voltage. The second pin P 2  is electrical connected to the switching unit  40 , and is used for generating the first control signal or the second control signal. The third pin P 3  is electrically connected to the voltage sampling circuit  50 , and is used for receiving the sampled voltage. 
     The switching unit  40  includes a first transistor Q 1 , and a second transistor Q 2 , a first resistor R 1 , a first protecting resistor Ra, and a second protecting resistor Rb. A base of the first transistor Q 1  is electrically connected to the second pin P 2  through the first protecting resistor Ra. An emitter of the first transistor Q 1  is grounded. A collector of the first transistor Q 1  is electrically connected to the power terminal V 1  through the first resistor R 1 . A gate of the second transistor Q 2  is electrically connected to the collector of the first transistor Q 1  through the second protecting resistor Rb. A drain of the second transistor Q 2  is electrically connected to the power terminal V 1 . A source of the second transistor Q 2  is electrically connected to the voltage sampling circuit  50 . In the embodiment, the first transistor Q 1  is an npn type bipolar junction transistor, and the second transistor Q 2  is a n-channel enhancement type metal oxide semiconductor field effect transistor. 
     The voltage sampling circuit  50  includes a second resistor R 2 , a third resistor R 3 , a first capacitor C 1 , a second capacitor C 2 , and a node N 1 . An end of the second resistor R 2  is electrically connected to the source of the second transistor Q 2 , and the other end of the second resistor R 2  is grounded via the node N 1  and the third resistor R 3  in that order. One end of the first capacitor C 1  is electrically connected to the node N 1 . The other end of the first capacitor C 1  is grounded. The second capacitor C 2  is electrically connected in parallel with the first capacitor C 1 . In the embodiment, the resistance of the resistor R 1  is larger then the sum of the resistance of the second resistor R 2  and the third resistor R 3 . 
     When the electronic device  100  is powered on, the second pin P 2  outputs the second control signal. The difference in voltage between the base and the emitter of the first transistor Q 1  is less than 0.7V and the first transistor Q 1  is turned off. The voltage at the gate of the second transistor Q 2  is equal to that of the power terminal V 1 , thus the difference in voltage between the source and the gate of the second transistor Q 2  is greater than 0.7V and the second transistor Q 2  is turned on. The first discharging path formed by the second transistor Q 2 , the second resistor R 2 , and the third resistor R 3  is thus established. The second discharging path formed by the first transistor Q 1  and the first resistor R 1  is cut off. The third pin P 3  receives the sampled voltage from the node N 1  to monitor the voltage of the power terminal V 1 . 
     When the electronic device  100  is powered off, the second pin P 2  outputs the first control signal. The difference in voltage between the base and the emitter of the first transistor Q 1  is greater than 0.7V and the first transistor Q 1  is turned on. The voltage at the gate of the second transistor Q 2  is almost 0V. The difference in voltage between the source and the gate of the second transistor Q 2  is thus less than 0.7V and the second transistor Q 2  is turned off. The first discharging path formed by the second transistor Q 2 , the second resistor R 2 , and the third resistor R 3  is cut off. A second discharging path formed by the first transistor Q 1  and the first resistor R 1  is established. 
     As described, the resistance of the first resistor R 1  is larger than the sum of the resistance of the second resistor R 2  and the third resistor R 3 , thus the electrical energy loss by the battery can be reduced. Therefore, the life of the battery is extended. 
     It is to be understood, however, that even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.