Light emitting diode backlight system the driving apparatus and driving method thereof

• US 9,113,520 B2
• Filed: 03/15/2013
• Issued: 08/18/2015
• Est. Priority Date: 12/17/2012
• Status: Active Grant

• Current Assignee: Power Forest Technology Corporation
• Original Assignee: Power Forest Technology Corporation
• Inventors: Lin, Hsiu-Ping
• Primary Examiner(s): HOUSTON, ADAM D
• Application Number:
  US13/831,718
• Publication Number:
  US 20140167630A1
• Time in Patent Office: 886 Days
• Field of Search: 315/186, 315/210
• US Class Current: 1/1
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

A light emitting diode (LED) backlight system and a driving apparatus and a driving method thereof are provided. The driving apparatus is suitable for an LED backlight system with N LED strings, where N is a positive integer greater than 1, and which includes an LED driver and a switching unit. The LED driver is configured to receive a dimming signal and time-divisionally generate N control signals in response to a counting clock and an enabling time and a period time both related to the dimming signal. The switching unit is coupled to the LED driver and the N LED strings, and is configured to respectively control an on-off time ratio of a current flowing through each of the LED strings in response to the N control signals.

Claims

1. A driving apparatus of a light emitting diode (LED) backlight system, wherein the LED backlight system has N LED strings, where N is a positive integer greater than 1, and the driving apparatus comprising:

an LED driver, configured to receive a dimming signal and time-divisionally generate N control signals by means of purely digital manner in response to a counting clock and an enabling time and a period time both related to the dimming signal, wherein enabling times of the time-divisionally generated N control signals are partially overlapped from each other; and

a switching unit, coupled to the LED driver and the LED strings, and configured to respectively control an on-off time ratio of a current flowing through each of the LED strings in response to the control signals.

2. The driving apparatus of the LED backlight system according to claim 1, wherein the LED driver comprises:

a first counter, configured to receive the dimming signal and count the dimming signal in response to the counting clock so as to obtain an enabling counting value and a period counting value that respectively represent the enabling time and the period time, wherein a frequency of the counting clock is substantially greater than a frequency of the dimming signal;

a divider, coupled to the first counter, and configured to divide the period counting value by N so as to obtain a delay value;

a pulse signal generator, coupled to the divider, and configured to time-divisionally generate N pulse signals within the period time of the dimming signal in response to the dimming signal, the counting clock and the delay value; and

N second counters, coupled to the first counter and the pulse signal generator, and configured to time-divisionally generate the control signals in response to the enabling counting value, the counting clock and the pulse signals.

3. The driving apparatus of the LED backlight system according to claim 1, wherein the switching unit comprises:

N switches, respectively corresponding to the LED strings and respectively controlling the on-off time ratio of the current flowing through each of the LED strings in response to the control signals.

4. The driving apparatus of the LED backlight system according to claim 1, wherein the LED strings are operated under a same system voltage, and the driving apparatus further comprises:

a boost-buck unit, configured to receive a direct-current (DC) input voltage and perform a boost-buck process on the DC input voltage by employing a pulse width modulation (PWM) control mechanism so as to generate and output the system voltage.

5. The driving apparatus of the LED backlight system according to claim 4, wherein the boost-buck unit further steadily outputs the system voltage in response to a feedback voltage from the LED driver.

6. An LED backlight system, comprising:

N LED strings, where N is a positive integer greater than 1; and

a driving apparatus, coupled to the LED strings, and configured to receive a dimming signal and time-divisionally generate N control signals by means of purely digital manner in response to a counting clock and an enabling time and a period time both related to the dimming signal, wherein enabling times of the time-divisionally generated N control signals are partially overlapped from each other, and the driving apparatus further respectively controls an on-off time ratio of a current flowing through each of the LED strings by a switching means in response to the control signals.

7. The LED backlight system according to claim 6, wherein the driving apparatus comprises:

an LED driver, configured to receive the dimming signal and time-divisionally generate the control signals in response to the counting clock and the enabling time and the period time both related to the dimming signal; and

a switching unit, coupled to the LED driver and the LED strings, and configured to respectively control the on-off time ratio of the current flowing through each of the LED strings in response to the control signals.

8. The LED backlight system according to claim 7, wherein the LED driver comprises:

a first counter, configured to receive the dimming signal and count the dimming signal in response to the counting clock so as to obtain an enabling counting value and a period counting value that respectively represent the enabling time and the period time, wherein a frequency of the counting clock is substantially greater than a frequency of the dimming signal;

a divider, coupled to the first counter, and configured to divide the period counting value by N so as to obtain a delay value;

a pulse signal generator, coupled to the divider, and configured to time-divisionally generate N pulse signals within the period time of the dimming signal in response to the dimming signal, the counting clock and the delay value; and

N second counters, coupled to the first counter and the pulse signal generator, and configured to time-divisionally generate the control signals in response to the enabling counting value, the counting clock and the pulse signals.

9. The LED backlight system according to claim 7, wherein the switching unit comprises:

N switches, respectively corresponding to the LED strings and respectively controlling the on-off time ratio of the current flowing through each of the LED strings in response to the control signals.

10. The LED backlight system according to claim 7, wherein the LED strings are operated under a same system voltage, and the driving apparatus further comprises:

a boost-buck unit, configured to receive a DC input voltage and perform a boost-buck process on the DC input voltage by employing a PWM control mechanism so as to generate and output the system voltage.

11. The LED backlight system according to claim 10, wherein the boost-buck unit further steadily outputs the system voltage in response to a feedback voltage from the LED driver.

12. A driving method of an LED backlight system, wherein the LED backlight system has N LED strings, where N is a positive integer greater than 1, and the driving method comprising:

time-divisionally generating N control signals by means of purely digital manner according to a counting clock and an enabling time and a period time both related to a dimming signal, wherein enabling times of the time-divisionally generated N control signals are partially overlapped from each other; and

respectively controlling an on-off time ratio of a current flowing through each of the LED strings according to the control signals.

13. The driving method of the LED backlight system according to claim 12, wherein the step of time-divisionally generating the control signals comprises:

counting the dimming signal according to the counting clock so as to obtain an enabling counting value and a period counting value that respectively represent the enabling time and the period time, wherein a frequency of the counting clock is substantially greater than a frequency of the dimming signal;

dividing the period counting value by N so as to obtain a delay value;

time-divisionally generating N pulse signals within the period time of the dimming signal according to the dimming signal, the counting clock and the delay value; and

time-divisionally generating the control signals by a counting means according to the enabling counting value, the counting clock and the N pulse signals.

14. The driving method of the LED backlight system according to claim 12, wherein the step of respectively controlling the on-off time ratio of the current flowing through each of the LED strings comprises:

respectively controlling the on-off time ratio of the current flowing through each of the LED strings by a switching means according to the control signals.

15. The driving method of the LED backlight system according to claim 12, wherein the LED strings are operated under a same system voltage, and before the step of time-divisionally generating the control signals, the driving method further comprises:

performing a boost-buck process on a DC input voltage by employing a PWM control mechanism so as to generate the system voltage.

16. The driving method of the LED backlight system according to claim 15, wherein after generating the system voltage, the driving method further comprises:

making the system voltage to be steadily outputted in response to a feedback voltage.