US3848945A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Brightness limiting circuit
Assignee: Thomas International Corp
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Filing: 1973-03-16
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Granted: 1974-11-19
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Expires: 1993-03-16
Abstract
Abstract A brightness limiting circuit for a television receiver reduces anode current in a CRT to prevent damage to the horizontal output stage by controlling the biasing of a transistor in series between the video amplifier and the chroma demodulator which drives the cathodes of the CRT. The transistor bias is developed from dual sensing circuits, one circuit comprising an RC network responsive to an excessive average anode current, and the other circuit comprising a switching network responsive to instantaneous peaks of anode current.
Inventors
- 👤 R Holzrichter
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 07:19
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/44; H04N5/57; H04N5/59
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
104 words
In a television receiver including a cathode ray tube having cathode means and anode means, and a high voltage anode power supply connected to said anode means to provide anode current which is related to cathode current, a limiting circuit responsive to both instantaneous peak current and average current in the cathode ray tube, comprising: means actuable for limiting the current to the cathode ray tube, peak current monitoring means responsive to a sensed instantaneous peak cathode ray tube current for Actuating said limiting means, and average current monitoring means responsive to a sensed average cathode ray tube current for actuating said limiting means.
Claim 2
Dependent Claim
104 words
In a television receiver including a cathode ray tube having cathode means and anode means, and a high voltage anode power supply connected to said anode means to provide anode current which is related to cathode current, a limiting circuit responsive to both instantaneous peak current and average current in the cathode ray tube, comprising: means actuable for limiting the current to the cathode ray tube, peak current monitoring means responsive to a sensed instantaneous peak cathode ray tube current for Actuating said limiting means, and average current monitoring means responsive to a sensed average cathode ray tube current for actuating said limiting means.
Claim 3
Dependent Claim
33 words
The limiting circuit of claim 1 wherein said peak current monitoring means comprises switching means for actuating said limiting means only when the instantaneous peak cathode ray tube current exceeds a predetermined value.
Claim 4
Dependent Claim
59 words
The limiting circuit of claim 2 wherein said switching means comprises resistive means connected with the high voltage anode power supply to produce a voltage drop thereacross proportional to current to the anode means, and a semiconductor breakover device coupled to said resistive means and responsive when the voltage drop exceeds a predetermined value for actuating the limiting means.
Claim 5
Dependent Claim
36 words
The limiting circuit of claim 3 wherein the semiconductor breakover device has a reverse leakage which undesirably tends to actuate the limiting means, and capacitor means for integrating instantaneous small changes produced by the reverse leakage.
Claim 6
Dependent Claim
104 words
The limiting circuit of claim 1 wherein the limiting means comprises a controllable conduction device for controlling the cathode beam current in the cathode ray tube, the high voltage anode power supply comprises a high voltage winding of a flyback transformer, rectifier means, a source of reference potential, and circuit means connecting the high voltage winding and the rectifier means in series between the source of reference potential and the anode means of the cathode ray tube to supply anode current thereto, the average current monitoring means and the peak current monitoring means being responsive to sensed anode current flowing in the circuit means.
Claim 7
Dependent Claim
64 words
The limit circuit of claim 5 wherein the average current monitoring means includes first resistive means connected in said series circuit means for developing thereacross a voltage proportional to anode current, and capacitor means coupled to said first resistive means for producing for the controllable conduction device a control signal proportional to the excessive average amount of anode current through the first resistive means.
Claim 8
Dependent Claim
58 words
The limiting circuit of claim 6 wherein the peak current monitoring means includes second resistive means connected in said series circuit means for developing thereacross a voltage proportional to anode current, and switching means coupled to said second resistive means and responsive only to a voltage in excess of a predetermined value for actuating the controllable conduction device.
Claim 9
Dependent Claim
40 words
The limiting circuit of claim 7 wherein the switching means comprises a Zener diode having one side coupled to said second resistive means and the other side coupled to the base of transistor means corresponding to the controllable conduction device.
Claim 10
Dependent Claim
101 words
In a television receiver including a cathode ray tube having cathode means and anode means, and a high voltage anode power supply coupled to said anode means, a brightness limiting circuit, comprising: semiconductor means connected in series with a circuit for supplying cathode current to limit cathode current flow from the cathode ray tube in response to a control signal, instantaneous peak sensing means for sensing instantaneous peaks of cathode ray tube current, including control means responsive to an instantaneous current peak in excess of a predetermined value for instantaneously generating said control signal to immediately limit cathode ray tube current.
Claim 11
Dependent Claim
101 words
In a television receiver including a cathode ray tube having cathode means and anode means, and a high voltage anode power supply coupled to said anode means, a brightness limiting circuit, comprising: semiconductor means connected in series with a circuit for supplying cathode current to limit cathode current flow from the cathode ray tube in response to a control signal, instantaneous peak sensing means for sensing instantaneous peaks of cathode ray tube current, including control means responsive to an instantaneous current peak in excess of a predetermined value for instantaneously generating said control signal to immediately limit cathode ray tube current.
Claim 12
Dependent Claim
70 words
The brightness limiting circuit of claim 9 wherein said instantaneous peak sensing means includes a voltage breakover device corresponding to said control means and switchable to a conduction state which produces said control signal, resistive means having a voltage drop thereacross which controls the voltage breakover device, and means connecting said resistive means in a circuit which has a current flow proportional to anode current to the cathode ray tube.
Claim 13
Dependent Claim
76 words
The brightness limiting circuit of claim 10 wherein said high voltage Anode power supply includes a high voltage winding of a flyback transformer, rectifier means for coupling one side of the high voltage winding to the anode means of the cathode ray tube, and said circuit connecting means connects the other side of the high voltage winding to a source of reference potential to cause the anode current to flow in series through the resistive means.
Claim 14
Dependent Claim
39 words
The brightness limiting circuit of claim 11 wherein the output of the voltage breakover device is directly coupled to the semiconductor means to limit cathode current flow substantially instantaneously in response to voltage breakover of the voltage breakover device.
Claim 15
Dependent Claim
38 words
The brightness limiting circuit of claim 9 including means for sensing the average current to the cathode ray tube, and means responsive to an excessive sensed average current for developing a second control signal for the semiconductor means.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-11-18 | 1978-05-20 | 1978-11-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-11-18 | 1982-05-20 | 1982-11-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-11-18 | 1986-05-20 | 1986-11-19 | $7700.00 | Window Closed / Lapsed |