Circuit and method for driving discharge lamp

• US 20060061304A1
• Filed: 09/21/2005
• Published: 03/23/2006
• Est. Priority Date: 09/22/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Han, Hee-Seok, Cho, Gyu-Hyeong, Kim, Sang-Kyung
• Granted Patent: US 7,242,155 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: H05B 41/2822 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• CPC Class Codes: H05B 41/2824 using control circuits for the switching element H05B41/2822 takes precedence
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

A discharge lamp driving circuit includes an inverter, a ballast capacitor, a discharge lamp, and a lamp current detecting circuit. The inverter converts a DC voltage into an AC voltage with high frequency to output the AC voltage to an output port based on a pulse width modulation control signal. The lamp current detecting circuit outputs a first voltage signal and a second voltage signal according to a voltage across the ballast capacitor to generate a lamp current sensing voltage that is proportional to a lamp current flowing through the discharge lamp. The pulse width modulation control signal has a width varying with amplitude of the lamp current so that the lamp current may be accurately detected.

Claims

1. A discharge lamp driving circuit, comprising:

a discharge lamp power source configured to generate an AC voltage across an output port thereof;

a ballast capacitor having a first electrode electrically coupled to a first terminal of the output port; and

a lamp current detecting circuit electrically coupled to the first electrode and a second electrode of said ballast capacitor and a second terminal of the output port.

2. The driving circuit of claim 1, wherein said lamp current detecting circuit is configured to generate first and second voltages;

and wherein a difference in the first and second voltages is proportional to a current through said ballast capacitor.

3. The driving circuit of claim 2, further comprising:

a signal processing unit responsive to the first and second voltages; and

a pulse-width modulation control circuit having an output electrically coupled to said discharge lamp power source and an input electrically coupled to an output of said signal processing unit.

4. The driving circuit of claim 1, wherein said lamp current detecting circuit comprises:

a first capacitor having a first electrode electrically connected to the first electrode of said ballast capacitor;

a second capacitor having a first electrode electrically connected to a second electrode of said first capacitor and a second electrode electrically connected to the second terminal of the output port;

a third capacitor having a first electrode electrically connected to the second electrode of said ballast capacitor; and

a fourth capacitor having a first electrode electrically connected to a second electrode of said third capacitor and a second electrode electrically connected to the second terminal of the output port.

5. The driving circuit of claim 4, wherein said lamp current detecting circuit further comprises:

a first resistor having a first terminal electrically coupled to the second electrode of said first capacitor and the first electrode of said second capacitor; and

a second resistor having a first terminal electrically coupled to the second electrode of said third capacitor and the first electrode of said fourth capacitor.

6. The driving circuit of claim 4, wherein a capacitance of each of said first, second, third and fourth capacitors is less than about one-tenth a capacitance of said ballast capacitor.

7. The driving circuit of claim 6, further comprising a printed circuit board;

and wherein the first and second electrodes of said first, second, third and fourth capacitors are defined by metal traces on opposite sides of the printed circuit board.

8. The driving circuit of claim 3, wherein said signal processing unit comprises a differential amplifier having first and second input terminals configured to receive the first and second voltages.

9. The driving circuit of claim 8, wherein said signal processing unit further comprises a voltage converting circuit configured to rectify a signal generated at an output of the differential amplifier.

10. The driving circuit of claim 5, wherein said lamp current detecting circuit is configured to generate first and second voltages at the first terminal of said first resistor and the first terminal of said second resistor, respectively;

and wherein a difference in the first and second voltages is proportional to a current through said ballast capacitor.

11. A discharge lamp driving circuit, comprising:

an inverter configured to convert a DC voltage into an AC voltage with high frequency to output the AC voltage to an output port based on a pulse width modulation control signal;

a ballast capacitor having a first terminal coupled to a first terminal of the output port of the inverter;

a discharge lamp coupled between a second terminal of the ballast capacitor and a second terminal of the output port of the inverter; and

a voltage detecting circuit, coupled between the first and second terminals of the output port of the inverter, configured to output a first voltage signal and a second voltage signal to generate a first sensing voltage proportional to a voltage across the first and second terminals of the output port of the inverter.

12. The discharge lamp driving circuit of claim 11, wherein the voltage detecting circuit includes:

a first capacitor having a first terminal commonly coupled to the first terminal of the output port of the inverter and the first terminal of the ballast capacitor;

a first resistor coupled between a second terminal of the first capacitor and the ground;

a second capacitor having a first terminal coupled to the second terminal of the output port of the inverter; and

a second resistor coupled between a second terminal of the second capacitor and the ground.

13. The discharge lamp driving circuit of claim 12, wherein the first voltage signal is outputted at a node where the first capacitor and the first resistor are connected, and the second voltage signal is outputted at a node where the second capacitor and the second resistor are connected, and wherein the difference between the first voltage signal and the second voltage signal corresponds to the first sensing voltage.

14. The discharge lamp driving circuit of claim 12, wherein the first capacitor and the second capacitor have the same capacitance with each other and the first resistor and the second resistor have the same resistance with each other.

15. The discharge lamp driving circuit of claim 14, wherein each of the first through fourth capacitors has much less capacitance than a capacitance of the ballast capacitor.

16. The discharge lamp driving circuit of claim 15, wherein the first sensing voltage is expressed as

VSSV=VSEC×

jω

C×

RB

wherein VSSV denotes the first sensing voltage, VSEC denotes the voltage across the first and second terminals of the output port of the inverter, C denotes the capacitance of each of the first capacitor and the second capacitor, and RB denotes the resistance of each of the first resistor and the second resistor.

17. The discharge lamp driving circuit of claim 12, wherein the first through fourth capacitors are implemented using a printed circuit board as a dielectric material of the first through fourth capacitors and traces arrayed on opposing sides of the printed circuit board as electrodes of the first through fourth capacitors.

18. The discharge pump driving circuit of claim 11, further comprising:

a signal processing unit configured to amplify and rectify a difference between the first voltage signal and the second voltage signal to generate a third voltage signal; and

a pulse width modulation control circuit configured to compare the third voltage signal with a reference signal to generate the pulse width modulation control signal having a width varying with the first sensing voltage.

19. The discharge lamp driving circuit of claim 18, wherein the signal processing unit includes:

a differential amplifier configured to amplify the difference between the first voltage signal and the second voltage signal; and

a voltage converting circuit configured to rectify an output signal of the differential amplifier to detect a peak value of the output signal of the differential amplifier.

20. The discharge lamp driving circuit of claim 11, wherein the signal detecting circuit further outputs a third voltage signal and a fourth voltage signal according to a voltage across the ballast capacitor to generate a second sensing voltage that is proportional to a lamp current flowing through the discharge lamp.

21-38. -38. (canceled)