CCFL circuit with independent adjustment of frequency and duty cycle

• US 6,911,786 B2
• Filed: 07/16/2003
• Issued: 06/28/2005
• Est. Priority Date: 07/16/2003
• Status: Expired due to Fees

• Current Assignee: Golden Long Teng Development Co. Ltd.
• Original Assignee: Analog Microelectronics Incorporated
• Inventors: Qiu, Weiguang
• Primary Examiner(s): TRAN, THUY V
• Application Number:
  US10/621,746
• Publication Number:
  US 20050012470A1
• Time in Patent Office: 713 Days
• Field of Search: 315/291, 315/55, 315246-247, 315293-294, 315/299, 315307-308, 315/DIG.2, 315/DIG.5, 315/DIG.7, 315/209.PZ
• US Class Current: 315/209.0PZ
• CPC Class Codes: H05B 41/2827 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 41/3921 with possibility of light intensity variations

Abstract

Two independent control variables, i.e. the frequency and the duty cycle of the driving waveform to an output driver, can be used to optimize the operation of a cold cathode fluorescent lamp (CCFL). The frequency of the driving waveform can be used to control the gain of a piezoelectric transformer (PZT) in a CCFL circuit. In contrast, the duty cycle of the driving waveform can be used to control the amplitude of the sinusoidal waveform at the PZT input terminal, and thus the current through the CCFL.

Claims

1. A method of optimizing performance of a cold cathode fluorescent lamp (CCFL) circuit, the CCFL circuit including a CCFL and a piezoelectric transformer (PZT) for driving the CCFL, the method comprising:

providing a driving waveform to the CCFL circuit,

wherein a frequency of the driving waveform is based on a linearly translated input source voltage, and

wherein a duty cycle of the driving waveform is based on a detected current through the CCFL.

2. The method of claim 1, wherein the linearly translated input source voltage is based on characteristics of the PZT in the CCFL circuit.

3.The method of claim 2, wherein the linearly translated input source voltage is based on a potential input voltage range for the CCFL circuit.

3. The method of claim 1, wherein providing the driving waveform includes turning on/off transistors of a half bridge in the CCFL circuit.

4. A method of optimizing performance of a cold cathode fluorescent lamp (CCFL) circuit, the CCFL circuit including a CCFL and a piezoelectric transformer (PZT) for driving the CCFL, the method comprising:

before operation of the CCFL circuit, determining a frequency of a driving waveform for the CCFL circuit, wherein the frequency is based on a range of input source voltages and a range of desired linearly translated source voltages associated with the PZT; and

during operation of the CCFL circuit, adjusting a duty cycle of the driving waveform based on a detected current through the CCFL.

5. A system for optimizing performance of a cold cathode fluorescent lamp (CCFL) circuit, the CCFL circuit including a CCFL and a piezoelectric transformer (PZT) for driving the CCFL, the system comprising:

means for determining a frequency of a driving waveform for the CCFL circuit, wherein the frequency is based on a range of input source voltages and a range of desired linearly translated source voltages associated with the PZT; and

means for adjusting a duty cycle of the driving waveform based on a detected current through the CCFL.

6. The system of claim 6, wherein the means for determining the frequency of the driving waveform includes:

a first resistor coupled between a node and a high voltage source, wherein the high voltage source is one voltage in the range of input source voltages;

a second resistor coupled between the node and a low voltage source;

an error amplifier having a positive input terminal connected to a reference voltage and a negative input terminal; and

a resistor coupled to the node, the negative input terminal of the error amplifier, and an output terminal of the error amplifier.

7. A linear voltage translator comprising:

a first resistor coupled between a node and a high voltage source, wherein the high voltage source is one voltage in a range of input source voltages;

a second resistor coupled between the node and a low voltage source;

an error amplifier having a positive input terminal connected to a reference voltage and a negative input terminal; and

a third resistor coupled to the node, the negative input terminal of the error amplifier, and an output terminal of the error amplifier.

8. The linear voltage translator of claim 8, wherein the output terminal of the error amplifier provides a signal to a voltage controlled oscillator (VCO) to determine an output frequency of the VCO.