Driving circuit for piezoelectric transformer, cold-cathode tube light-emitting apparatus, liquid crystal panel and device with built-in liquid crystal panel

• US 7,145,281 B2
• Filed: 08/31/2005
• Issued: 12/05/2006
• Est. Priority Date: 11/29/2001
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Nakatsuka, Hiroshi, Takeda, Katsu, Moritoki, Katsunori
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US11/217,004
• Publication Number:
  US 20050285478A1
• Time in Patent Office: 461 Days
• Field of Search: 310/316.01, 310/318, 310/319
• US Class Current: 310/316.01
• 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 41/2855 against abnormal lamp operating conditions
• CPC Class Codes: H05B 41/392 using semiconductor devices, e.g. thyristor
• CPC Class Codes: H10N 30/804 for piezoelectric transformers conversion of DC or AC power H02M; for operating discharge lamps H05B41/282

Abstract

A driving circuit for a piezoelectric transformer is provided, which ensures lighting of all the cold-cathode tubes connected to the piezoelectric transformer, and reduces the difference in brightness between the cathode tubes during steady lighting, thereby enhancing reliability and performance. A plurality of cold-cathode tubes connected to a secondary side of the piezoelectric transformer, and a cold-cathode tube output detector circuit connected in series to a plurality of cold-cathode tubes, for detecting an output state of the respective cold-cathode tubes are provided, and the driving of the piezoelectric transformer is controlled based on a detection signal from the cold-cathode tube output detector circuit. Because of this, the piezoelectric transformer performs the same operation as that with respect to one cold-cathode tube.

Claims

1. A cold-cathode tube light-emitting apparatus, comprising:

a piezoelectric transformer including a primary side electrode and a secondary side electrode formed on a piezoelectric body and converting an AC voltage input from the primary side electrode to output the converted AC voltage from the secondary side electrode;

a plurality of cold-cathode tubes connected to a secondary side of the piezoelectric transformer;

a cold-cathode tube output detector portion connected in series to the plurality of cold-cathode tubes, for electrically separating and detecting a current flowing through the respective cold-cathode tubes; and

a control portion for controlling light-emission of the plurality of cold-cathode tubes based on a detection signal from the cold-cathode tube output detector portion.

2. The cold-cathode tube light-emitting apparatus according to claim 1, wherein the piezoelectric body has a rectangular shape and the secondary side electrode of the piezoelectric transformer is provided on each end face of the piezoelectric body in a longitudinal direction, and polarization directions of the piezoelectric body in a vicinity of the secondary side electrodes are the same in the longitudinal direction.

3. The cold-cathode tube light-emitting apparatus according to claim 2, wherein the number of the cold-cathode tubes is 2n (n is an integer of 1 or more).

4. The cold-cathode tube light-emitting apparatus according to claim 2, wherein the cold-cathode tube output detector portion includes an optical isolator composed of a light-emitting diode and a phototransistor.

5. The cold-cathode tube light-emitting apparatus according to claim 2, wherein the piezoelectric transformer and the control portion are mounted on a first substrate placed in proximity to one electrode of each of the plurality of cold-cathode tubes, and the cold-cathode tube output detector portion is mounted on a second substrate placed in proximity to the other electrode of each of the plurality of cold-cathode tubes.