Inverter

• US 8,044,604 B2
• Filed: 04/08/2009
• Issued: 10/25/2011
• Est. Priority Date: 04/08/2008
• Status: Expired due to Fees

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Hagino, Junichi, Fukumoto, Kenichi
• Primary Examiner(s): Ismail; Shawki S
• Assistant Examiner(s): Hammond; Crystal L
• Application Number:
  US12/420,274
• Publication Number:
  US 20090251062A1
• Time in Patent Office: 930 Days
• Field of Search: None
• US Class Current: 315/276
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 7/5387 in a bridge configuration
• CPC Class Codes: H02P 7/29 using pulse modulation
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence

Abstract

A soft start circuit generates a soft start voltage which changes over time when light emission of an EEFL is started. A pulse modulator receives a feedback voltage that corresponds to the output voltage of an inverter and the soft start voltage, and adjusts the duty ratio of a pulse signal PWM such that these two voltages match one another using a feedback operation. A striking control circuit monitors an error signal which is asserted when an abnormal state occurs. In a case in which the error signal has been asserted at a detection timing after the soft start voltage has reached a target voltage, the striking control circuit resets and restarts the soft start circuit. A driver controls the switching of the voltage at the primary coil of a transformer according to the pulse signal received from the pulse modulator.

Claims

1. A control circuit for an inverter which drives an external electrode fluorescent lamp connected to a secondary line of a transformer, the control circuit comprising:

a soft start circuit structured to generate a soft start voltage which changes over time when the external electrode fluorescent lamp is ignited;

a pulse modulator structured to receive a feedback voltage that corresponds to the output voltage of the inverter and the soft start voltage, and structured to adjust the duty ratio of a pulse signal such that the feedback voltage matches the soft start voltage;

a driver structured to control the switching of the voltage at a primary coil of the transformer according to the pulse signal output from the pulse modulator; and

a striking control circuit structured to monitor an error signal which is asserted when an abnormal state occurs, and structured to reset and restart the soft start circuit when the error signal has been asserted at a detection timing after the soft start voltage has reached a threshold voltage.

2. A control circuit according to claim 1, wherein the striking control circuit comprises a counter structured to count the number of times the soft start circuit has been reset,

and wherein, in a case in which the count value has reached a predetermined value, the soft start circuit is prevented from being reset.

3. A control circuit according to claim 1, wherein the soft start circuit further comprises:

a capacitor, one terminal of which is set to a fixed electric potential;

a current source structured to charge the capacitor; and

a first comparator structured to compare the soft start voltage, which occurs at the other terminal of the capacitor, with a predetermined first threshold voltage,

and wherein, when the soft start circuit is reset, the striking control circuit switches an initializing switch, provided between the one terminal of the capacitor and a fixed voltage terminal, to the ON state, and when the soft start voltage is reduced to a predetermined threshold voltage, the striking control circuit switches the initializing switch to the OFF state.

4. An inverter comprising:

a transformer;

control circuit according to claim 1, which is structured to control the switching of the voltage at the primary coil of the transformer; and

a voltage detection unit structured to detect the output voltage of the inverter, which is generated at the secondary coil of the transformer, and which structured to output a voltage that corresponds to the output voltage to the control circuit.

5. A liquid crystal display apparatus including:

a liquid crystal panel;

an external electrode fluorescent lamp provided as a backlight for the liquid crystal panel; and

an inverter according to claim 4, the output voltage of which is supplied to the external electrode fluorescent lamp.

6. A control method for an inverter which drives an external electrode fluorescent lamp, the method comprising:

generating a soft start voltage which changes over time when the external electrode fluorescent lamp is ignited;

adjusting a duty ratio of a pulse signal such that a feedback voltage that corresponds to output voltage of the inverter matches the soft start voltage;

controlling switching of the voltage at a primary coil of a transformer according to the pulse signal; and

monitoring an error signal which is asserted when an abnormal state occurs, and striking the external electrode fluorescent lamp by initializing the soft start voltage and by changing the soft start voltage over time when the error signal has been asserted at a detection timing after the soft start voltage has reached a threshold voltage.

7. A control method according to claim 6, further comprising counting the number of times the soft start voltage has been initialized,

wherein, in a case in which the count value has reached a predetermined value, the soft start circuit is prevented from being reset.