Bus controller

Abstract

A power supply apparatus is provided, that supplies a bus voltage VBUS to a detachable device. A DC/DC converter generates a DC voltage VOUT used as the bus voltage VBUS. A USB controller receives the DC voltage VOUT as a power supply voltage, and detects whether or not the device is connected. The DC/DC converter generates the DC voltage VOUT such that (i) when the device is detected, the DC voltage VOUT has a specified voltage level, and such that (ii) when the device is not detected, the DC voltage VOUT has a voltage level that is lower than the specified voltage level and that is higher than a minimum operating voltage level required to operate the USB controller.

What is claimed is: 
     
         1 . A bus controller that is employed together with a DC/DC converter that generates a DC voltage used as a bus voltage to be supplied to a detachable device, and that is configured as a power supply apparatus, wherein the DC/DC converter comprises:
 a transformer having a primary winding and a secondary winding;   a secondary-side rectifier circuit that is connected to the secondary winding, so as to output the DC voltage;   a switching transistor connected to the primary winding;   a photocoupler comprising a light-emitting element and a light-receiving element;   a feedback circuit comprising a shunt regulator that is connected to the light-emitting element of the photocoupler, and that drives the light-emitting element with a current that corresponds to a difference between a detection voltage that corresponds to the DC voltage and a reference voltage;   a primary-side controller that switches on and off the switching transistor according to a feedback signal that corresponds to a current that flows through the light-receiving element of the photocoupler; and   the bus controller arranged on a secondary side of the transformer, and that detects whether or not the device is connected or disconnected,   and wherein the bus controller comprises:
 a power supply terminal that is connected to an output of the secondary-side rectifier circuit, and that receives the DC voltage as a power supply voltage; 
 a detector that detects whether or not the device is connected; and 
 a feedback control unit that controls the feedback circuit such that (i) when the device is detected, the DC voltage is generated so as to have a specified voltage level, and such that (ii) when the device is not detected, the DC voltage is generated so as to have a voltage level that is lower than the specified voltage level and that is higher than a minimum operating voltage required to operate the bus controller. 
   
     
     
         2 . The bus controller according to  claim 1 , wherein the power supply apparatus further comprises:
 a connector to which the device is detachably connected; and   an output switch arranged between the output of the secondary-side rectifier circuit and the connector,   and wherein the power supply terminal of the bus controller is connected between the output of the secondary-side rectifier circuit and the output switch.   
     
     
         3 . The bus controller according to  claim 2 , further comprising a switch control unit that performs a control operation such that (i) when the device is detected, the output switch is turned on, and such that (ii) when the device is not detected, the output switch is turned off. 
     
     
         4 . The bus controller according to  claim 1 , further comprising a communication unit that communicates with the device,
 wherein the feedback control unit selects one from among a plurality of specified voltage levels based on a communication between the communication unit and the device.   
     
     
         5 . The bus controller according to  claim 1 , wherein the feedback control unit switches the reference voltage so as to switch the voltage level of the DC voltage. 
     
     
         6 . The bus controller according to  claim 1 , wherein the feedback circuit further comprises a voltage dividing circuit that divides the DC voltage with a variable voltage dividing ratio so as to generate the detection voltage,
 and wherein the feedback control unit switches the voltage dividing ratio of the voltage dividing circuit so as to switch the voltage level of the DC voltage.   
     
     
         7 . The bus controller according to  claim 1 , monolithically integrated on a single semiconductor substrate. 
     
     
         8 . The bus controller according to  claim 1 , that conforms to the USB Type-C specification. 
     
     
         9 . The bus controller according to  claim 1 , that conforms to the USB-PD specification. 
     
     
         10 . The bus controller according to  claim 1 , that conforms to the Quick Charge specification. 
     
     
         11 . A power supply adapter that supplies a bus voltage to a detachable device, the power supply adapter comprising:
 an input rectifier circuit that rectifies an AC voltage;   a DC/DC converter that receives an output voltage of the input rectifier circuit so as to generate a DC voltage to be used as the bus voltage; and   the bus controller according to  claim 1 .   
     
     
         12 . A power supply apparatus that supplies a bus voltage to a detachable device, the power supply apparatus comprising:
 a DC/DC converter that generates a DC voltage used as the bus voltage; and   a bus controller that receives the DC voltage as a power supply voltage, and that detects whether or not the device is connected,   wherein the DC/DC converter generates the DC voltage such that (i) when the bus controller detects the device, the DC voltage has a specified voltage level, and such that (ii) when the bus controller detects no device, the DC voltage has a voltage level that is lower than the specified voltage level and that is higher than a minimum operating voltage required to operate the bus controller.   
     
     
         13 . The power supply apparatus according to  claim 12 , further comprising:
 a connector via which the device is detachably connected; and   an output switch arranged between an output of the DC/DC converter and the connector,   wherein a power supply terminal of the bus controller is connected between the output of the DC/DC converter and the output switch.   
     
     
         14 . The power supply apparatus according to  claim 13 , that performs a control operation such that (i) when the device is detected, the output switch is turned on, and such that (ii) when the device is not detected, the output switch is turned off. 
     
     
         15 . The power supply apparatus according to  claim 12 , wherein the bus controller selects one from among a plurality of specified voltage levels according to a negotiation between the bus controller and the device. 
     
     
         16 . The power supply apparatus according to  claim 12 , wherein the DC/DC converter is configured as an insulated DC/DC converter,
 and wherein the DC/DC converter comprises:
 a transformer having a primary winding and a secondary winding; 
 a secondary-side rectifier circuit that is connected to the secondary winding, so as to output the DC voltage; 
 a switching transistor connected to the primary winding; 
 a photocoupler comprising a light-emitting element and a light-receiving element; 
 a feedback circuit comprising a shunt regulator that is connected to the light-emitting element of the photocoupler, and that drives the light-emitting element with a current that corresponds to a difference between a detection voltage that corresponds to the DC voltage and a reference voltage; and 
 a primary-side controller that switches on and off the switching transistor according to a feedback signal that corresponds to a current that flows through the light-receiving element of the photocoupler. 
   
     
     
         17 . The power supply apparatus according to  claim 16 , wherein the bus controller switches the reference voltage so as to switch the voltage level of the DC voltage. 
     
     
         18 . The power supply apparatus according to  claim 16 , wherein the feedback circuit further comprises a voltage dividing circuit that divides the DC voltage with a variable voltage dividing ratio so as to generate the detection voltage,
 and wherein the bus controller switches the voltage dividing ratio of the voltage dividing circuit so as to switch the voltage level of the DC voltage.   
     
     
         19 . The power supply apparatus according to  claim 12 , that conforms to the USB Type-C specification. 
     
     
         20 . The power supply apparatus according to  claim 12 , that conforms to the USB-PD specification.