Display device and method for controlling display device for reducing current requiremeents for driving light source units

• US 9,202,421 B2
• Filed: 04/24/2013
• Issued: 12/01/2015
• Est. Priority Date: 04/24/2012
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamamura, Akihiro, Matsuda, Isao
• Primary Examiner(s): Snyder, Adam J
• Application Number:
  US13/869,588
• Publication Number:
  US 20130278651A1
• Time in Patent Office: 951 Days
• Field of Search: 345/102
• US Class Current: 1/1
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2330/025 Reduction of instantaneous peaks of current
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

A display device has a display panel and a backlight unit. The backlight unit includes first and second light source units, and a control unit that outputs a drive signal to the light source units to drive the first and second light source units during first and second drive periods in one frame period respectively. The control unit drives the light source units so that the one frame period has an overlapped period, in which the first and second drive periods overlap. The control unit outputs PWM signals to turn the light source units on and off to the light source units respectively. The control unit shifts a phase of the PWM signal to be outputted to the first light source unit and a phase of the PWM signal to be outputted to the second light source unit from each other.

Claims

1. A display device, comprising:

a display panel that displays a frame image for each one frame period; and

a backlight unit that illuminates the display panel from a rear face of the display panel, wherein

the backlight unit includes;

a first light source unit that illuminates the display panel;

a second light source unit that illuminates the display panel; and

a control unit that outputs a drive signal to the first light source unit to drive the first light source unit during a first drive period in the one frame period, and a drive signal to the second light source unit to drive the second light source unit during a second drive period in the one frame period after the driving of the first light source unit is started, and

the control unit;

drives the first light source unit and the second light source unit so that the one frame period has an overlapped period, in which the first drive period and the second drive period overlap each other;

outputs a PWM signal as the drive signal to the first light source unit in the overlapped period, and a PWM signal as the drive signal to the second light source unit in the overlapped period, each of the PWM signals turning the first light source unit and the second light source unit on and off with a predetermined pulse width;

shifts a phase of the PWM signal to be outputted to the first light source unit and a phase of the PWM signal to be outputted to the second light source unit from each other,

outputs, as the drive signal, a rectangular wave signal to the first light source unit during a period other than the overlapped period in the first drive period, to drive the first light source unit so that a current value of the first light source unit becomes a first current value; and

outputs, as the drive signal, a rectangular wave signal to the second light source unit during a period other than the overlapped period in the second drive period, to drive the second light source unit so that a current value of the second light source unit becomes a second current value,

wherein the control unit increases, when outputting the PWM signal, a current value to be larger than the first current value when the first light source unit is on, and increases, when outputting the PWM signal, a current value to be larger than the second current value when the second light source unit is on,

each of the periods other than the overlapped period in the first drive period is longer than each period of the PWM signals turning the first light source unit on, and

each of the periods other than the overlapped period in the second drive period is longer than each period of the PWM signals turning the second light source unit on.

2. The display device according to claim 1, wherein the control unit shifts the phase of the PWM signal to be outputted to the first light source unit and the phase of the PWM signal to be outputted to the second light source unit from each other, so that an on period of the first light source unit and an on period of the second light source unit do not overlap in the overlapped period.

3. The display device according to claim 1, wherein the control unit outputs the PWM signal to the first light source unit during the first drive period, and outputs the PWM signal to the second light source unit during the second drive period.

4. The display device according to claim 1, wherein the control unit sets a current value of the first light source unit so that an effective value of the current of the first light source unit becomes constant during the first drive period, and sets a current value of the second light source unit so that an effective value of the current of the second light source unit becomes constant during the second drive period.

5. The display device according to claim 1, wherein the first light source unit and the second light source unit include light emitting diodes respectively.