Drive circuit for a cathode ray tube

• US 5,604,404 A
• Filed: 11/07/1995
• Issued: 02/18/1997
• Est. Priority Date: 01/21/1993
• Status: Expired due to Term

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Sahara, Hiroshi
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): SHINGLETON, MICHAEL B
• Application Number:
  US08/554,799
• Time in Patent Office: 469 Days
• Field of Search: 315/344, 315/8, 315/383, 330/254
• US Class Current: 315/8
• CPC Class Codes: H03G 3/10 having semiconductor devices
• CPC Class Codes: H04N 5/148 Video amplifiers amplifiers in general H03F
• CPC Class Codes: H04N 5/57 Control of contrast or brightness
• CPC Class Codes: H04N 5/59 in dependence upon beam current of cathode ray tube

Abstract

A video signal is supplied from an emitter coupled differential amplifier to a first grid electrode of a cathode ray tube. A blanking pulse signal is supplied to the base of a transistor, which constitutes a constant-current source for the differential amplifier, to put the transistor into an on-state to obtain a voltage of a blanking level to apply blanking. Since the transistor is controlled by a switching control to apply blanking, a transistor of a high voltage-resisting property is not required, and the power loss is reduced. The differential amplifier operates stably and does not deteriorate the frequency characteristic or the response characteristic.

Claims

1. A drive circuit for a flat cathode ray tube having a cathode electrode, a first grid electrode and a second grid electrode, comprising:

a high-voltage generator receiving horizontal drive pulses for generating a first fixed DC voltage supplied to said cathode electrode, a fixed voltage supplied to said second grid electrode of said cathode ray tube, a high voltage supplied to said cathode ray tube, and a second fixed DC voltage;

a differential amplifier for supplying a video signal for producing a video display on said cathode ray tube;

means connected to said high-voltage generator and to said differential amplifier for combining said second fixed DC voltage and said video signal and for adjusting said second fixed DC voltage to effect cutoff adjustment and to supply a combined DC voltage and video signal to said first grid electrode of said cathode ray tube, said cutoff adjustment and said fixed voltage supplied to said second grid electrode being mutually independent; and

a constant-current source for supplying a constant current to said differential amplifier and for switching said differential amplifier to blank said video signal according to a blanking pulse signal,

wherein said high-voltage generator includes a secondary coil that operates independently from said differential amplifier to produce a pulsed voltage, said cathode electrode being energized by said first fixed DC voltage and also by said pulsed voltage.

2. A drive circuit for a cathode ray tube according to claim 1, wherein said constant-current source includes a current mirror circuit, and switching control means for controlling switching of a transistor of said current mirror circuit according to said blanking pulse signal.

3. A drive circuit for a flat cathode ray tube having a cathode electrode, a first grid electrode and a second grid electrode, comprising:

means for applying a first fixed DC voltage to said cathode electrode, a fixed voltage to said second grid electrode, and a high voltage to said cathode ray tube;

a differential amplifier for supplying a video signal;

means for combining a second DC voltage and said video signal supplied by said differential amplifier, for varying said second DC voltage to effect cutoff adjustment, and for supplying a combined DC voltage and video signal to said first grid electrode of said cathode ray tube, said cutoff adjustment and said fixed voltage applied to said second grid electrode being mutually independent;

a constant-current source for supplying a constant current to said differential amplifier;

a switch circuit connected in parallel to said constant-current source for switching said differential amplifier; and

switching control means for controlling switching of said differential amplifier by said switch circuit to blank said video signal according to a blanking pulse signal,

wherein said means for applying includes a secondary coil that operates independently from said differential amplifier to produce a pulsed voltage, said cathode electrode being energized by said first fixed DC voltage and also by said pulsed voltage.

4. A drive circuit for a cathode ray tube according to claim 3, wherein said switch circuit includes a diode in series with a transistor.

5. A drive circuit for a cathode ray tube according to claim 3, wherein said fixed voltage applied to said second grid electrode is a fixed DC high voltage, said cutoff adjustment and said fixed DC high voltage supplied to said second grid electrode being mutually independent.