Patent Publication Number: US-2015084579-A1

Title: Charging circuit

Description:
BACKGROUND 
     The present invention relates to circuits for charging electronic devices and, more particularly, to circuits for charging portable electronic devices such as laptop computers, tablet computers, smartphones, and the like. 
     Portable electronic devices need to be charged periodically. Different types of devices, however, require different voltages and/or charging profiles in order to properly charge. Chargers are usually only configured to charge one type of device or group of devices having the same charging profile. 
     SUMMARY 
     In one embodiment, the invention provides a charging circuit for charging a portable electronic device. The charging circuit includes a port configured to be coupled to the portable electronic device, a power switch coupled to the port and configured to be coupled to a power supply, and a control circuit coupled to the power switch and the port. The power switch is switchable between an open state and a closed state. The control circuit is operable to control the power switch based on an amount of charging current drawn by the portable electronic device through the port. 
     In another embodiment the invention provides a charging circuit for charging a portable electronic device from a power supply. The charging circuit includes a port configured to be coupled to the portable electronic device, a power switch coupled to the port and configured to be coupled to the power supply, an oscillator coupled to the power switch, a current-to-voltage converter coupled to the port and the power switch, and a comparator coupled to the oscillator and the current-to-voltage converter. The power switch is switchable between an open state and a closed state. The oscillator is operable to oscillate the power switch between the open and closed states. The current-to-voltage converter is operable to convert an amount of current drawn by the portable electronic device through the port into the voltage. The comparator is operable to stop oscillation of the oscillator when the voltage exceeds a reference voltage to hold the power switch in the closed state and charge the portable electronic device. 
     In another embodiment the invention provides a method of charging a portable electronic device. The method includes connecting a portable electronic device to the port, oscillating the power switch between an open state and a closed state, converting a current drawn by the portable electronic device into a voltage, comparing the voltage to a reference value, outputting a signal from the comparator to the oscillator to stop oscillating, holding the power switch in the closed stated when the voltage meets a condition with respect to the reference voltage, and charging the portable electronic device. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a charging circuit embodying the invention. 
         FIG. 2  is a timing diagram of the charging circuit shown in  FIG. 1 . 
         FIG. 3  is a schematic diagram of another charging circuit embodying the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
       FIG. 1  illustrates a charging circuit  10  for charging a portable electronic device  11 . In some embodiments, the charging circuit  10  may be part of a cabinet or other structure that is designed to receive and store a plurality of portable electronic devices  11  simultaneously. In such embodiments, the charging circuit  10  charges several electronic devices  11  at a time. The charging circuit  10  automatically begins charging the electronic device  11  if the electronic device  11  recognizes the charging circuit  10  as a suitable charging circuit. In further embodiments, such as the illustrated embodiment, the charging circuit  10  is also configured to sync data on the portable electronic device  11 . 
     The portable electronic device  11  may be, for example, a laptop computer, a tablet computer, a smartphone, a cellphone, or a two-way radio. In some embodiments, the portable electronic device  11  may be an IPAD tablet computer sold by Apple, Inc. In other embodiments, other types of portable electronic devices that periodically require charging may be connected to the circuit  10 . The electronic device  11  can include a USB port, a micro USB port, or another suitable power and/or data port to connect the device  11  to the charging circuit  10 . 
     The charging circuit  10  is configured to connect the electronic device  11  to a power supply  12  (e.g., a 120 volt AC wall outlet) to charge the device  11  using power from the power supply  12 . If necessary, the output of the power supply  12  is reduced to a voltage suitable for charging the electronic device  11 . For example, a 120 volt AC power supply can include an AC/DC converter to convert the output of the power supply to a DC voltage, and can include a DC/DC converter to reduce the voltage of the power supply. Alternatively, the output of the power supply could be reduced by only an AC/DC converter. In the illustrated embodiment, the power supply  12  includes circuitry to reduce the output to 5 volts DC. In other embodiments, the power supply  12  may be configured to output other desired voltages. 
     The illustrated charging circuit  10  includes a port  13 , a power switch  14 , and a control circuit  16 . The port  13  is coupled to the power switch  14  and configured to be coupled to the electronic device  11 . In the illustrated embodiment, the port  13  is a USB port that is configured to be coupled to the port of electronic device  11  by a cable. In other embodiments, the port  13  may be plugged directly into the port of the electronic device  11  without a cable. The USB port  13  includes a Vbus port, a D+ port, and a D− port. The Vbus port is coupled to the power supply  12  through the power switch  14  to supply power to the electronic device  11 . The D+ and D− ports help ensure that the charging circuit  10  is recognized as a suitable charging circuit by the electronic device  11 . 
     The power switch  14  is coupled to the port  13  and to the power supply  12 . The power switch  14  switches between an open state, in which the port  13  is disconnected from the power supply  12 , and a closed state, in which the port  13  is connected to the power supply  12 . When the power switch  14  is in the closed state, the power supply  12  provides charging current to the electronic device  11  through the port  13 . 
     The control circuit  16  is coupled to the port  13  and the power switch  14  to control operation of the charging circuit  10 . In particular, the control circuit  16  controls whether the power switch  14  is held in the closed state to charge the electronic device. The control circuit  16  detects when the electronic device  11  is connected to the port  13 . The control circuit  16  also holds the power switch  14  in the closed state if the electronic device  11  recognizes the charging circuit  10  as a suitable charging circuit for the connected electronic device  11 . 
     The illustrated control circuit  16  includes a resistor network  20 , an oscillator  22 , a comparator  24 , and a current-to-voltage converter  26 . The resistor network  20  is coupled to the port  13  and simulates a plug-in profile for the electronic device  11 . The resistor network  20  allows the electronic device  11  to identify the charging circuit  10  as a recognized charging circuit. In the illustrated embodiment, the resistor network  20  is coupled to the D+ and D− ports of the electronic device  11  through the port  13  to perform an identification protocol. Depending on the type of electronic device  11  that is coupled to the charging circuit the identification protocol is different. For example, for an IPAD tablet computer sold by Apple, Inc., the identification protocol includes applying a first reference voltage to the D+ port and a second reference voltage to the D− port. As another example, some electronic devices are compliant to USBIF identification protocol. The USBIF protocol includes shorting the D+ and the D− ports on the electronic device. In the illustrated embodiment, a switch  29  (e.g., a USB switch) selectively connects the resistor network  20  to the port  13  to control the connections to the D+ and D− ports. The USB switch  29  determines which connections to make to the D+ and D− ports of the USB port  13 . When the switch  29  connects the resistor network  20  to the port  13  and the electronic device  11  has recognized the charging circuit  10 , the electronic device  11  begins to draw a current through the port  13 . 
     The comparator  24  is coupled the current-to-voltage converter  26 , the oscillator  22 , and a reference voltage  28 . The comparator  24  compares a signal from the current-to-voltage converter  26  to the reference voltage  28 . The comparator  24  is operable to output a Hi signal or a Lo signal to the oscillator  22  based on the comparison between the signal from the current-to-voltage converter  26  and the reference voltage  28 . For example, if the voltage signal from the current-to-voltage converter  26  is lower than the reference voltage  28 , the comparator  24  outputs the Hi signal (or logic “1”) to the oscillator  22 . If the voltage signal from the current-to-voltage converter  26  is higher than the reference voltage  28 , the comparator  24  outputs the Lo signal (or logic “0”) to the oscillator  22 . 
     The current-to-voltage converter  26  is coupled to the comparator  24 , the power switch  14 , and the port  13 . The current-to-voltage converter  26  detects a current drawn by the electronic device  11  through the port  13 . The current-to-voltage converter  26  outputs a voltage signal to the comparator  24  proportional to the amount of current drawn by the electronic device  11 . In the illustrated embodiment, the current-to-voltage converter  26  includes a precision resistor  38  and an amplifier  40 . The precision resistor  38  is coupled to the power switch  14  and the port  13 . The amplifier  40  is coupled to the comparator  24  and is coupled in parallel to the precision resistor  38 . The amplifier  40  converts the current through the precision resistor  38  into a voltage signal that feeds into the comparator  24 . In other embodiments, other suitable current-to-voltage converters may also or alternatively be employed. For example, in some embodiments, the current-to-voltage converter  26  may be part of an integrated circuit that converts an input current to a proportional voltage signal. 
     The oscillator  22  is coupled to the power switch  14  and the comparator  24 . The oscillator  22  may be any type of suitable multivibrator such as, for example, an astable multivibrator, monostable multivibrator, or bistable multivibrator. In the illustrated embodiment, the oscillator is an astable multivibrator. The oscillator receives the Hi and Lo signals from the comparator  24 , which control the operation of the oscillator  22 . When the oscillator  22  receives the Hi signal (or logic “1”) from the comparator  24 , the oscillator  22  will run freely and generate a pulse train. The pulse train continually cycles the power switch  14  between the open and closed states. When the oscillator  22  receives the Lo signal (or logic “0”) from the comparator  24 , the oscillator  22  stops generating the pulse train and latches the power switch  14  in the closed state. In some embodiments, the oscillator  22  can include two logic gates, two resistors, and a capacitor to selectively generate the pulse train and control operation of the power switch  14 . In such embodiments, the logic gates may be NAND gates. In other embodiments, other suitable oscillators may also or alternatively be employed. 
     In the illustrated embodiment, the charging circuit  10  also includes a sync switch  56 . The illustrated sync switch  56  is a manual actuator such as, for example, a push button, a pivotable switch, a rotatable knob, or the like. In other embodiments, the sync switch  56  may be an electronic switch that is automatically actuated in response to certain conditions of the charging circuit  10  and/or the device  11 . The sync switch  56  selectively couples the control circuit  16  (and, thereby, the electronic device  11 ) to sync data on the device  11 . The sync switch  56  is operable to switch between two states: an open state, in which the electronic device  11  is disconnected from the host device  58 , and a closed state, in which the electronic device  11  is coupled to the host device  58 . The illustrated sync switch  56  is coupled to the electronic device  11  through the USB switch  29  and the port  13 . When the sync switch  56  is closed to connect the electronic device  11  to the host device  58 , data transmission occurs through the switch  29  and the port  13  so that the electronic device  11  syncs with the host device  58 . In some embodiments, the charging circuit  10  includes a plurality of ports  13  to connect multiple electronic devices  11  to the circuit simultaneously. In such embodiments, the sync switch  56  controls data transmission between the host device  58  and each of the electronic devices  11  connected to the ports  13 . 
     The illustrated sync switch  56  is also coupled to the oscillator  22  to override operation of the control circuit  16 . When the sync switch  56  is in the closed state, a signal (i.e., a Lo signal or logic “0”) is sent to the oscillator  22  to hold the power switch  14  in the closed state. In this state, the electronic device  11  draws a charging current from the power supply  12  depending on, for example, the capability of the host device  58 , a protocol of the host device  58 , and the availability of a compatible protocol in the electronic device  11 . The current-to-voltage converter  26  and the comparator  24  continue to function as described above, but the output of the comparator  24  is overridden by the sync switch  56  to inhibit oscillation of the power switch  14 . 
     In the illustrated embodiment, the charging circuit  10  also includes an indicator  60 . The indicator  60  provides a visual and/or audible indication to a user regarding whether the connected electronic device  11  is charging, syncing, or both. In the illustrated embodiment, the indicator  60  is a light emitting diode (LED), although other suitable indicators may also or alternatively be employed. The indicator  60  can be turned on continuously, can flash, or can blink to indicate the current state of the electronic device  11 . Additionally or alternatively, the indicator  60  may display different colors, each of which represents a different status of the electronic device  11 . In some embodiments, the charging circuit  10  may include a plurality of indicators (e.g., two indicators). In such embodiments, one indicator could indicate when the connected electronic device  11  is charging, while the other indicator could indicate when the connected electronic device  11  is syncing. 
     In some embodiments, the comparator  24  can control additional components of the charging circuit  10 . For example, the comparator  24  can inhibit operation of the charging circuit  10  based on the current drawn by the portable electronic device  11 . Thus, if the current drawn by the portable electronic device  11  is too high for the components of the charging circuit  10 , the comparator  24  will output a signal to cease oscillation of the oscillator  22  and effectively shut down the charging circuit  10 . The comparator  24  may be coupled to a second reference voltage to prevent the current drawn by the portable electronic device  11  from exceeding a predetermined threshold. Also, the comparator  24  can output signals to the charging status indicator  60  to control the status of the indicator  60 . In addition, the comparator  24  can output signals to a cooling fan positioned adjacent the circuit  10  to turn the fan on and off. 
     In operation, a user connects the electronic device  11  to the port  13  of the charging circuit  10  to charge the device  11 . The control circuit  16  determines when the electronic device  11  is coupled to the charging circuit  10 . After the electronic device  11  recognizes the charging circuit  10  as a suitable charging circuit, the control circuit  16  (specifically, the comparator  24 ) outputs a signal to hold the power switch  14  in the closed state so that the electronic device  11  draws current from the power supply  12 . If the current drawn by the electronic device  11  exceeds a predetermined threshold, the control circuit  16  (specifically, the comparator  24 ) outputs a signal to cease operation of the charging circuit  10 . Alternatively, if the sync switch  56  is closed, the electronic device  11  syncs with the host device  58  and charges through the power switch  14 , regardless of the output from the control circuit  16 . 
       FIG. 2  is a timing diagram depicting operation of the charging circuit  10 . The timing diagram may be different depending on the type of multivibrator or oscillator used in the control circuit  16 . In the illustrated embodiment, the timing diagram corresponds to an embodiment where the oscillator  22  is an astable multivibrator. At Time 0, the electronic device  11  is not coupled to the port  13 . During this time, the comparator  24  outputs the Lo signal (logic “0”) so that the power switch  14  is in the open state, the sync switch  56  is open, and the port  13  receives 0 volts from the power supply  12 . 
     Time 1 depicts when the electronic device  11  is coupled to the port  13 . During this time, the sync switch  56  is still open, but the electronic device  11  is performing an identification procedure with the charging circuit  10 . The comparator  24  outputs the Hi signal (logic “1”) so that the power switch  14  oscillates between the open state and the closed state. As the power switch  14  oscillates, the port  13  alternately receives 0 volts and 5 volts from the power supply  12  (i.e., the port  13  receives 0 volts when the power switch  14  is in the open state and receives 5 volts when the power switch  14  is in the closed state). 
     Time 2 depicts when the electronic device  11  recognizes the charging circuit  10  as a suitable circuit for charging. That is, the voltage from the current-to-voltage converter  26  is higher than the reference voltage  28  so that the comparator outputs the Lo signal (logic “0”) to the oscillator  22 . During Time 2, the sync switch  56  remains open, and the power switch  14  is held in the closed state. As such, the port  13  receives 5 volts from the power supply  12  to charge the connected electronic device  11 . 
     Time 3 depicts when the sync switch  56  is closed. During this time, the sync switch  56  outputs a signal to the oscillator  22  to inhibit the oscillator  22  (and, thereby, the power switch  14 ) from oscillating. The power switch  14  remains in the closed state so that the port  13  receives 5 volts from the power supply  12 . Thus, during Time 3, the electronic device  11  syncs with the host device  58  and, if necessary, charges. 
       FIG. 3  illustrates another charging circuit  100  for charging the portable electronic device  11 . The charging circuit  100  includes similar components as the charging circuit  10  shown in  FIG. 1 , and like parts have been given the same reference numbers. 
     In the illustrated embodiment, the control circuit  16  of the charging circuit  100  includes a plurality of resistor networks  62  and a multiplexer  64 . Each resistor network  63  (e.g., resistor network  1  through resistor network N) simulates a different plug-in profile for different electronic devices. When an electronic device is coupled to the port  13 , the multiplexer  64  cycles through the different resistor networks  63  until the appropriate resistor network  63  is identified by the connected device  11 . Once the electronic device  11  identifies the appropriate resistor network  63 , the output from the current-to-voltage converter  26  becomes larger than the reference voltage  28  such that the comparator  24  outputs the Lo signal (logic “0”) to the oscillator  22  to hold the power switch  14  in the closed state. 
     The illustrated multiplexer  64  is coupled to the oscillator  22  such that the multiplexer  64  cycles through the resistor networks  63  concurrently with the power switch  14  oscillating between the open and closed states. For example, each time the power switch  14  switches to the open state, a counter within the multiplexer  64  increases by one to move on to the next resistor network  63 . When the power switch  14  then switches back to the closed state, the next resistor network  63  in the series is coupled to the port  13  through the multiplexer  64 . 
     In other embodiments, a manual switch may be used to connect the appropriate resistor network  63  to the electronic device  11  for recognition by the electronic device  11 . In such embodiments, the manual switch may be actuated by a user to cycle through the resistor networks  63 . For example, the manual switch may include a rotary dial, one or more push-buttons, a toggle switch, or the like, such that different positions of the manual switch correspond to different resistor networks  63 . 
     Other operations of the charging circuit  100  to charge and sync the electronic device  11  are substantially the same as the charging circuit  10  discussed above. 
     Various features and advantages of the invention are set forth in the following claims.