Driving LED's

• US 20120154260A1
• Filed: 09/02/2010
• Published: 06/21/2012
• Est. Priority Date: 09/09/2009
• Status: Abandoned Application

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Decraemer, Alain, De Meersman, Erik
• Application Number:
  US13/390,744
• Publication Number:
  US 20120154260A1
• Time in Patent Office: Days
• US Class Current: 345/82
• 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: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A drive circuit (DR) drives a plurality of LED strings (DS1, DS2; DS10) each comprising at least one LED (Di). The drive circuit comprises a resonance inductor (K1), and a plurality of branches which each comprise a series arrangement of a resonance capacitor (C31, C32; C34, C35) and an associated one of the plurality of LED strings (DS1, DS2; DS10). The resonance capacitor (C31, C32; C34, C35) is arranged between the resonance inductor (K1) and its associated one of the plurality of LED strings (DS1, DS2; DS10) to receive a resonance voltage (VAC) from the resonance inductor (K1). A level and frequency of the resonance voltage (VAC) and an impedance of the resonance capacitor (C31, C32; C34, C35) are selected to obtain a current source supplying a LED current (IL1 IL2; IL10) through the associated one of the plurality of LED strings (DS1, DS2; DS10) which is substantially independent on a tolerance on forward voltages of LED'"'"'s of the associated one of the plurality of LED strings (DS1, DS2; DS10).

Claims

1. A drive circuit (DR) for driving a plurality of LED strings (DS1, DS2;

DS10) each comprising at least one LED (Di), the drive circuit comprises;

a resonance inductor (K1),

a plurality of branches each comprising a series arrangement of a resonance capacitor (C31, C32;

C34, C35) and an associated one of the plurality of LED strings (DS1, DS2;

DS10), the resonance capacitor (C31, C32;

C34, C35) being arranged between the resonance inductor (K1) and its associated one of the plurality of LED strings (DS1, DS2;

DS10) for receiving a resonance voltage (VAC) from the resonance inductor (K1),

wherein a level and frequency of the resonance voltage (VAC) and an impedance of the resonance capacitor (C31, C32;

C34, C35) are selected for supplying a LED current (IL1, IL2;

IL10) through the associated one of the plurality of LED strings (DS1, DS2;

DS10) being substantially independent on a tolerance on forward voltages of LED'"'"'s of the associated one of the plurality of LED strings (DS1, DS2;

DS10).

2. A drive circuit (DR) as claimed in claim 1, further comprising in each one of the plurality of branches a rectifier circuit (R1, R2;

Ri) arranged between the resonance capacitor (C31, C32;

C34, C35) and its associated one of the plurality of LED strings (DS1, DS2;

DS10).

3. A drive circuit (DR) as claimed in claim 2, further comprising an electronic switch (Q11, Q12;

Q1,Q2) coupled to a junction of the resonance capacitor (C31, C32;

C34, C35) and its associated one of the plurality of LED strings (DS1, DS2;

DS10) to withdraw at least a portion of the LED current (IL1, IL2;

IL10) from the junction.

4. A drive circuit (DR) as claimed in claim 1, wherein the resonance voltage (VAC) is a same common AC voltage for each one of the resonance capacitors (C31, C32;

C34, C35).

5. A drive circuit (DR) as claimed in claim 1, further comprising a power converter (PC) for supplying an AC power supply voltage (VA) to the resonance inductor (K1), and wherein the power converter (PC) has an input for influencing the AC power supply voltage (VA) to control the LED current (IL1, IL2;

IL10) through the LED strings (DS1, DS2;

DS10).

6. A drive circuit (DR) as claimed in claim 5, further comprising a control circuit (CC) receiving a video signal (VI) to be displayed on a display panel (DP) illuminated by the LED strings (DS1, DS2;

DS10), the control circuit (CC1) having an output coupled to the input of the power converter (PC) to control the LED current (IL1, IL2;

IL10) in response to the video signal (VI).

7. A drive circuit (DR) as claimed in claim 6, wherein the control circuit (CC1) is constructed for reducing the LED current (IL1, IL2;

IL10) when a white content in an image represented by the video signal (VI) exceeds a predetermined level or for increasing the LED current (IL1, IL2;

IL10) when a white content in an image represented by the video signal (VI) drops below a predetermined level.

8. A drive circuit (DR) as claimed in claim 1, further comprising a power converter (PC) for supplying an AC power supply voltage (VA) to the resonance inductor (K1), and a feedback circuit (FC), the feedback circuit (FC) comprises:

a feedback capacitor (C30) being one of the plurality of resonance capacitors,

an impedance (R1, R3) for supplying a feedback signal (VF) representative of a current (IL0) through the impedance (R1, R3), and

a rectifier circuit (D70, D80) being arranged between the feedback capacitor (C30) and the impedance (R1,R3),

wherein the power converter (PC) comprises a control circuit (CC2) having an input for receiving the feedback signal (VF) to regulate the AC power supply voltage (VA) in response to the feedback signal (VF).

9. A drive circuit (DR) as claimed in claim 8, further comprising a further control circuit (CC1) receiving a video signal (VI) to be displayed on a display panel (DP) illuminated by the LED strings (DS1, DS2;

DS10), the further control circuit (CC1) having an output coupled to the impedance (R1, R3) for influencing the feedback signal (VF) to control the LED current (IL1, IL2;

IL10) through the LED strings (DS1, DS2;

DS10) in response to the video signal (VI).

10. A drive circuit (DR) as claimed in claim 9, wherein the further control circuit (CC1) is constructed for reducing the LED current (IL1, IL2;

IL10) when a white content in a picture represented by the video signal (VI) exceeds a predetermined level, or for increasing the LED current (IL1, IL2;

IL10) when a white content in a picture represented by the video signal (VI) drops below a predetermined level.

11. A LED circuit comprising the drive circuit (DR) of claim 1 and the LED strings (DS1, DS2;

DS10).

12. A backlight unit (BL) for a display apparatus (DA), the backlight unit (BL) comprises the LED circuit of claim 11.

13. A display apparatus (DA) comprising a display panel (DP) and the backlight unit (BL) of claim 12 for illuminating the display panel (DP).