Method and apparatus for DC to AC power conversion for driving discharge lamps

• US 7,560,879 B2
• Filed: 01/18/2006
• Issued: 07/14/2009
• Est. Priority Date: 01/19/2005
• Status: Active Grant

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Chen, Wei
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US11/335,399
• Publication Number:
  US 20060158136A1
• Time in Patent Office: 1,273 Days
• Field of Search: 315/247, 315/246, 315/224, 315/225, 315/209.R, 315/291, 315307-311, 315/274, 315/279
• US Class Current: 315/308
• CPC Class Codes: H05B 41/2824 using control circuits for the switching element H05B41/2822 takes precedence
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

Abstract

Methods and circuits are disclosed for converting DC power to AC power for driving discharge lamps such as cold cathode fluorescent lamps (CCFLs). Among other advantages, the lamp current and open lamp voltage can be regulated by a simple control scheme.

Claims

1. A method of converting a DC input voltage to an AC signal, comprising:

controllably switching an input voltage ON and OFF to generate a (Pulse Width Modulated) PWM AC signal to drive a lamp;

receiving feedback signals from said lamp;

comparing said feedback signals with at least one reference signal to generate a control signal; and

controlling either the duty cycle signal or both the frequency and the duty cycle signal of said PWM AC signal depending upon the signal level of said control signal.

2. The method of claim 1, wherein said at least one reference signal comprises a first reference voltage and a second reference voltage, and wherein said second reference voltage at least equal to said first reference signal.

3. The method of claim 2, wherein when said control signal is greater than said second reference voltage, controlling both the frequency and the duty cycle of said PWM AC signal.

4. The method of claim 2, wherein when said control signal is less than said first reference voltage, controlling only the duty cycle of said PWM AC signal.

5. The method of claim 2, wherein when said control signal is greater than said second reference voltage, controlling only the frequency of said PWM AC signal.

6. The method of claim 2, wherein said feedback signals further comprise either a current signal or a voltage signal.