Power-supply apparatus and display apparatus

Abstract

A liquid crystal display apparatus is capable of reducing a power loss incurred by a power-supply section in a process of generating a power-supply voltage for driving a backlight section. In the configuration of the power-supply section, a main power-supply circuit and an inverter circuit (or a DC-DC converter) are connected to an input-voltage generation unit in parallel to each other, which is used for rectifying and smoothing the commercial alternative current power. The main power-supply circuit and the inverter circuit (or the DC-DC converter) each include an isolation transformer including a primary-side winding not isolated from the commercial alternative current power and a secondary winding provided on the secondary side. The direct current input voltage is supplied to the primary side to be subjected to a power conversion process to generate an output voltage on the secondary side of the isolation transformer. Thus, the number of power conversion process stages for supplying power to the backlight section connected to the inverter circuit (or the DC-DC converter) is reduced by 1. As a result, the power loss incurred by the power-supply section can be reduced to a value smaller than that of the conventional one.

The invention claimed is: 
     
       1. A display apparatus having a backlight section and a load other than said backlight section, said display apparatus comprising:
 an input-voltage generation section for generating a direct current input voltage from an alternating current;   a first power conversion section for receiving said direct current input voltage, and for carrying out a DC-DC power conversion process on the direct current input voltage to generate a direct current power-supply voltage to be supplied to said load;   a second power conversion section connected in parallel with said first power conversion section, and including:
 a primary side for receiving said direct current input voltage, and including:
 a pair of series connected switches for switching the direct current input voltage to generate an alternating current input voltage supplied to a primary winding of at least one transformer, and 
 a driving circuit for driving said pair of series connected switches, 
 
 a secondary side, isolated from said primary side by said at least one transformer, for generating, from an alternating current output voltage supplied by a secondary winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected backlights of said backlight section, 
 a detection circuit connected in series with only one of the plurality of parallel connected backlights for detecting a voltage supplied to that backlight, and 
 a feedback section for receiving the detected voltage from said detection circuit, for rectifying the detected voltage, and for supplying the rectified voltage to said driving circuit of said primary side of said second power conversion section, 
 said driving circuit controlling the quantity of light emitted by the plurality of parallel connected backlights to a constant value based on the rectified voltage; and 
   a display section for displaying a picture using said backlight section.   
     
     
       2. A display apparatus according to  claim 1 , wherein the at least one transformer includes a plurality of transformers each associated with a respective portion of the plurality of parallel connected backlights of said backlight section. 
     
     
       3. A display apparatus according to  claim 1 , wherein a plurality of parallel connected fluorescent tubes is employed as the plurality of parallel connected backlights of said backlight section, and said secondary side of said second power conversion section generates the power-supply voltage to be supplied to each of said parallel connected fluorescent tubes. 
     
     
       4. A display apparatus according to  claim 1 , wherein said input-voltage generation section includes a rectification/smoothing circuit having a plurality of diodes for rectifying the alternating current, and a capacitor for smoothing a rectified output of said plurality of diodes, and said input-voltage generation section generates said direct current input voltage as a voltage appearing between terminals of said capacitor. 
     
     
       5. A display apparatus according to  claim 1 , wherein said input-voltage generation section includes a power-factor improvement converter for generating a stabilized direct current output voltage as the direct current input voltage. 
     
     
       6. A display apparatus according to  claim 1 , wherein said feedback section isolates the primary and secondary sides of the second power conversion section from each other. 
     
     
       7. A display apparatus having a backlight section and a load other than the backlight section, the display apparatus comprising:
 an input-voltage generation section which generates a direct current input voltage from an alternating current;   a first power conversion section which receives the direct current input voltage, and carries out a DC-DC power conversion process on the direct current input voltage to generate a direct current power-supply voltage to be supplied to the load;   a second power conversion section connected in parallel with the first power conversion section, and including:
 a primary side which receives the direct current input voltage, and including:
 a pair of series connected switches which switches the direct current input voltage to generate an alternating current input voltage supplied to a primary winding of at least one transformer, and 
 a driving circuit which drives the pair of series connected switches, 
 
 a secondary side, isolated from the primary side by the at least one transformer, which generates, from an alternating current output voltage supplied by a secondary winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected backlights of the backlight section, 
 a detection circuit connected in series with only one of the plurality of parallel connected backlights for detecting a voltage supplied to that backlight, and 
 a feedback section which receives the detected voltage from the detection circuit, rectifies the detected voltage, and supplies the rectified voltage to the driving circuit of the primary side of the second power conversion section, 
 the driving circuit controlling the quantity of light emitted by the plurality of parallel connected backlights to a constant value based on the rectified voltage; and 
   a display section which displays a picture using the backlight section.   
     
     
       8. A display apparatus according to  claim 7 , wherein the at least one transformer includes a plurality of transformers each associated with a respective portion of the plurality of parallel connected backlights of the backlight section. 
     
     
       9. A display apparatus according to  claim 7 , wherein a plurality of parallel connected fluorescent tubes is employed as the plurality of parallel connected backlights of the backlight section. 
     
     
       10. A display apparatus according to  claim 7 , wherein the input-voltage generation section includes a rectification/smoothing circuit having a plurality of diodes which rectify the alternating current, and a capacitor which smoothes a rectified output of the plurality of diodes, and the input-voltage generation section generates the direct current input voltage as a voltage appearing between terminals of the capacitor. 
     
     
       11. A display apparatus according to  claim 7 , wherein the input-voltage generation section includes a power-factor improvement converter which generates a stabilized direct current output voltage as the direct current input voltage. 
     
     
       12. A display apparatus according to  claim 7 , wherein the feedback section isolates the primary and secondary sides of the second power conversion section from each other. 
     
     
       13. A display apparatus having a backlight section and a load other than the backlight section, the display apparatus comprising:
 an input-voltage generation section configured to generate a direct current input voltage from an alternating current;   a first power conversion section configured to generate a direct current power-supply voltage to be supplied to the load;   a second power conversion section configured to connect in parallel with the load, and including:   a primary side for receiving the direct current input voltage, and including:   an alternating switching device configured to switch the direct current input voltage to generate an alternating current input voltage supplied to a primary winding of at least one transformer,   a driving circuit configured to drive the alternating switching device,   a secondary side, isolated from the primary side by the at least one transformer, for generating, from an alternating current output voltage supplied by a secondary winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected backlights of the backlight section,   a detection circuit configured to connect in series with only one of the plurality of parallel connected backlights for detecting a voltage supplied to that backlight, and   a feedback section configured to receive a detected voltage from the detection circuit, for adjusting the detected voltage to generate an adjusted optical signal voltage, and for supplying the adjusted optical signal voltage to the driving circuit;   wherein the input-voltage generation section includes a power factor correction converter circuit for improving the power factor,   wherein the driving circuit is configured to control the quantity of light emitted by the plurality of parallel connected backlights to a constant value based on the adjusted optical signal voltage; and   wherein a display section is configured to display a picture using the backlight section.   
     
     
       14. A display apparatus according to claim 13, wherein the power factor correction converter circuit adopts a PWM control method for generating a stabilized direct current output voltage as the direct current input voltage. 
     
     
       15. A display apparatus according to claim 13, wherein the input-voltage generation section is configured to include a driving control circuit executing a PWM control based on the alternating current input voltage and differentials of the direct current input voltage to change the on duration of the alternating switching device. 
     
     
       16. A display apparatus according to claim 13, wherein the input-voltage generation section is configured to include an inductor and a recovery diode that are connected as a series circuit between a plus output terminal of a bridge rectification circuit and a plus terminal of an output capacitor. 
     
     
       17. A display apparatus according to claim 13, wherein the at least one transformer is a plurality of transformers, each associated with a respective portion of the plurality of parallel connected backlights of the backlight section. 
     
     
       18. A display apparatus according to claim 13, wherein the at least one transformer includes a plurality of secondary windings each associated with a respective portion of the plurality of parallel connected backlights of the backlight section. 
     
     
       19. A display apparatus according to claim 13, wherein the alternating switching device is configured to include a pair of series connected switches for switching the direct current input voltage. 
     
     
       20. A display apparatus according to claim 13, wherein the alternating switching device is connected to a first terminal of the primary winding of the at least one transformer, and a terminal of the alternating switching device is connected through a capacitor to a second terminal of the primary winding of the at least one transformer. 
     
     
       21. A display apparatus according to claim 13, wherein the alternating switching device is connected to the primary winding, and wherein one terminal of the alternating switching device is electrically connected to the primary winding by a capacitor. 
     
     
       22. A power-supply apparatus for generating a direct current power-supply voltage having a light driving section and a load other than the light driving section, the power-supply apparatus comprising:
 an input-voltage generation section configured to generate a direct current input voltage from an alternating current;   a first power conversion section configured to generate a direct current power-supply voltage to be supplied to the load;   a second power conversion section configured to connect in parallel with the load, and including:   a first power-supply side configured to receive the direct current input voltage, and including:   an alternating switching device configured to switch the direct current input voltage to generate an alternating current input voltage supplied to a first winding of at least one transformer,   a driving circuit configured to drive the alternating switching device,   a second power-supply side configured to generate from an alternating current output voltage supplied by a second winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected lights of the light driving section,   a detection circuit configured to connect in series with fewer than all of the plurality of parallel connected lights of the light driving section configured to detect a voltage supplied to the light driving section, and   a feedback section configured to receive a detected voltage from the detection circuit, for adjusting the detected voltage to generate an adjusted optical signal voltage, and for supplying the adjusted optical signal voltage to the driving circuit;   wherein the input-voltage generation section includes a power factor correction converter circuit for improving the power-factor;   wherein the driving circuit is configured to control the quantity of light emitted by the plurality of parallel connected lights of the light driving section to a constant value based on the adjusted optical signal voltage; and   wherein the light driving section is configured to drive a light source as the load.   
     
     
       23. A display apparatus according to claim 13, wherein the at least one transformer is a plurality of transformers that are parallel connected with respect to one another. 
     
     
       24. A power-supply apparatus according to claim 22, wherein the power factor correction converter circuit adopts a PWM control for generating a stabilized direct current output voltage as the direct current input voltage. 
     
     
       25. A power-supply apparatus according to claim 22, wherein the input-voltage generation section is configured to include a driving control circuit executing a PWM control based on the alternating current input voltage and differentials of the direct current input voltage to change the on duration of the alternating switching device. 
     
     
       26. A power-supply apparatus according to claim 22, wherein the input-voltage generation section is configured to include an inductor and a recovery diode that are connected as a series circuit between a plus output terminal of a bridge rectification circuit and a plus terminal of an output capacitor. 
     
     
       27. A power-supply apparatus of claim 22, wherein the at least one transformer is a plurality of transformers that are parallel connected with respect to one another. 
     
     
       28. A power-supply apparatus according to claim 22, wherein the alternating switching device is configured to include a pair of series connected switches for switching the direct current input voltage. 
     
     
       29. A power-supply apparatus according to claim 22, wherein the alternating switching device is connected to the first terminal of the primary winding of the at least one transformer, and a terminal of the alternating switching device is connected through a capacitor to the second terminal of the primary winding of the at least one transformer. 
     
     
       30. A power-supply apparatus according to claim 22, wherein the alternating switching device is connected to the primary winding, and wherein one terminal of the alternating switching device is electrically connected to the primary winding by a capacitor. 
     
     
       31. A display apparatus having a backlight section and a load other than the backlight section, the display apparatus comprising:
 an input-voltage generation section for generating a direct current input voltage from an alternating current;   a first power conversion section for generating a direct current power-supply voltage to be supplied to the load;   a second power conversion section connected in parallel with the first power conversion section, and including:   a primary side for receiving the direct current input voltage, and including:   switches for switching the direct current input voltage to generate an alternating current input voltage being supplied to a primary winding of at least one transformer,   a driving circuit for driving the switches,   a secondary side, isolated from the primary side by the at least one transformer, for generating, from an alternating current output voltage supplied by a secondary winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected backlight light emitting diode circuits, each of the backlight light emitting diode circuits including a plurality of light emitting diodes in series of the backlight section,   a voltage detection circuit for each of the backlight light emitting diode circuits, the voltage detection circuit connected in series with the backlight light emitting diode circuit for detecting a voltage supplied to the backlight light emitting diode circuits,   a feedback section for receiving the detected voltage from the voltage detection circuit, for adjusting the detected voltage to generate an adjusted optical signal voltage, and for supplying the adjusted optical signal voltage to the driving circuit of the primary side of the second power conversion section, and   the driving circuit controlling the quantity of light emitted by light emitting diodes of the plurality of parallel connected backlight light emitting diode circuits to a constant value based on the adjusted optical signal voltage; and   a display section for displaying a picture using the backlight section.   
     
     
       32. A display apparatus according to claim 31, wherein the junction point between the switches is connected to the primary winding, and wherein one terminal of the switches is electrically connected to the primary winding by a capacitor. 
     
     
       33. A display apparatus according to claim 31, wherein the plurality of transformers are parallel connected with respect to one another. 
     
     
       34. A display apparatus according to claim 31, wherein the at least one transformer is a plurality of transformers each associated with a respective portion of the plurality of parallel connected backlight light emitting diode circuits, each of the backlight light emitting diode circuits including a plurality of light emitting diodes in series of the backlight section. 
     
     
       35. A display apparatus according to claim 31, wherein the at least one transformer includes a plurality of secondary windings each associated with a respective portion of the plurality of parallel connected backlight light emitting diode circuits, each of the backlight light emitting diode circuits including a plurality of light emitting diodes in series of the backlight section. 
     
     
       36. A display apparatus according to claim 31, wherein the input-voltage generation section includes a power-factor improvement converter for generating a stabilized direct current output voltage as the direct current input voltage. 
     
     
       37. A display apparatus according to claim 31, wherein a junction located between the pair of series connected switches is connected to a first terminal of the primary winding of the at least one transformer, and a terminal of the switches is connected through a capacitor to a second terminal of the primary winding of the at least one transformer, wherein there are two switches in parallel for switching the direct current input voltage to generate the alternating current input voltage being supplied to the primary winding of the at least one transformer and driving circuit drives the two switches. 
     
     
       38. A power-supply apparatus for generating a direct current power-supply voltage having a backlight section and a load other than the backlight section, the power-supply apparatus comprising:
 an input-voltage generation section for generating a direct current input voltage from an alternating current;   a first power conversion section for generating a direct current power-supply voltage to be supplied to the load;   a second power conversion section connected in parallel with the first power conversion section, and including:   a first power-supply side for receiving the direct current input voltage, and including:   a pair of series connected switches for switching the direct current input voltage to generate an alternating current input voltage being supplied to a first winding of at least one transformer,   a driving circuit for driving the pair of series connected switches,   a second power-supply side, for generating, from an alternating current output voltage supplied by a second winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected backlight light emitting diode circuits, each of the backlight light emitting diode circuits including a plurality of light emitting diodes in series of the backlight section   a voltage detection circuit connected in series with one of the plurality of parallel connected the backlight section for detecting a voltage supplied to the backlight section,   a plurality of voltage detection circuits, each is connected in series with the backlight light emitting diode circuit for detecting a voltage supplied to the backlight light emitting diode circuits,   a feedback section for receiving the detected voltage from the voltage detection circuit, for adjusting the detected voltage to generate an adjusted optical signal voltage, and for supplying the adjusted optical signal voltage to the driving circuit of the first power-supply side of the second power conversion section, and   the driving circuit controlling the quantity of light emitted by light emitting diodes of the plurality of parallel connected backlight light emitting diode circuits to a constant value based on the adjusted optical signal voltage; and   the backlight section driving a light source as the load.   
     
     
       39. A power-supply apparatus of claim 38, wherein the at least one transformer is a plurality of parallel connected transformers. 
     
     
       40. A display apparatus having a backlight section and a load other than the backlight section, the display apparatus comprising:
 an input-voltage generation section for generating a direct current input voltage from an alternating current;   a first power conversion section for generating a direct current power-supply voltage to be supplied to the load;   a second power conversion section connected in parallel with the first power conversion section, and including:   a primary side for receiving the direct current input voltage, and including:   switches for switching the direct current input voltage to generate an alternating current input voltage being supplied to a primary winding of at least one transformer,   a driving circuit for driving the switches,   a secondary side, isolated from the primary side by the at least one transformer, for generating, from an alternating current output voltage supplied by a secondary winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected backlight light emitting diode circuits, each of the backlight light emitting diode circuits including a plurality of light emitting diodes in series the backlight section,   a voltage detection circuit connected with one of the plurality of parallel connected power conversion section,   a feedback section for receiving the detected voltage from the voltage detection circuit, for adjusting the detected voltage to generate an adjusted optical signal voltage, and for supplying the adjusted optical signal voltage to the driving circuit of the primary side of the second power conversion section, and   the driving circuit controlling the quantity of light emitted by light emitting diodes of the plurality of parallel connected backlight light emitting diode circuits to a stable value based on the adjusted optical signal voltage;   the voltage detection circuit for stabilizing a voltage to be supplied to the plurality of light emitting diodes in series; and   a display section for displaying a picture using the backlight section.   
     
     
       41. A power supply apparatus according to claim 40, wherein the input-voltage generation section includes a power-factor improvement converter for generating a stabilized direct current output voltage as the direct current input voltage. 
     
     
       42. A power supply apparatus of claim 40, wherein the at least one transformer is a plurality of parallel connected transformers. 
     
     
       43. A display apparatus according to claim 40, wherein the input-voltage generation section includes a power-factor improvement converter for generating a stabilized direct current output voltage as the direct current input voltage. 
     
     
       44. A display apparatus of claim 40, wherein the at least one transformer is a plurality of parallel connected transformers. 
     
     
       45. A power supply apparatus of claim 40, wherein the power-supply apparatus further includes a display section for displaying a picture. 
     
     
       46. A power supply apparatus having a light emitting diode circuit section and a load other than the light emitting diode circuit section, the display apparatus comprising:
 an input-voltage generation section for generating a direct current input voltage from an alternating current;   a first power conversion section for generating a direct current power-supply voltage to be supplied to the load;   a second power conversion section connected in parallel with the first power conversion section, and including:   a primary side for receiving the direct current input voltage, and including:   switches for switching the direct current input voltage to generate an alternating current input voltage being supplied to a primary winding of at least one transformer,   a driving circuit for driving the switches,   a secondary side, isolated from the primary side by the at least one transformer, for generating, from an alternating current output voltage supplied by a secondary winding of the at least one transformer, a power-supply voltage to be supplied to a plurality of parallel connected a plurality of light emitting diode connected to each other, each of the light emitting diode circuits including a plurality of light emitting diodes in series,   a voltage detection circuit connected with one of the plurality of parallel connected power conversion section,   a feedback section for receiving the detected voltage from the voltage detection circuit, for adjusting the detected voltage to generate an adjusted optical signal voltage, and for supplying the adjusted optical signal voltage to the driving circuit of the primary side of the second power conversion section, and   the driving circuit controlling the quantity of light emitted by light emitting diodes of the plurality of parallel connected light emitting diode circuits to a constant value based on the adjusted optical signal voltage;   the voltage detection circuit for stabilizing a voltage to be supplied to the plurality of light emitting diodes in series; and   a display section for displaying a picture using the light emitting diode circuit section.