# US 4,393,336 A · Regulation of the EHT voltage of a CRT

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- Number: US 4,393,336 A
- Document ID: US4393336A
- Status: Granted
- Kind: A
- Application number: 06/250,262
- Filed: 1981-04-02
- Granted: 1983-07-12
- Earliest claimed: 1980-12-23
- Assignees: Electrohome Limited
- Inventors: Terrance C. Schmidt
- Web page: https://patentgrep.com/patent/US4393336A

## CPC

- H04N 3/185: Maintaining DC voltage constant
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

The frequency of operation of a tuned flyback type transformer is controlled by a voltage controlled oscillator whose output frequency varies with EHT in such a way that EHT tends to stay constant despite beam current or input voltage variations.

## Claims

### Claim 1

In combination with a cathode ray tube having an anode; means for deriving and supplying EHT to said anode other than via horizontal deflection circuitry that supplies deflection current to the horizontal deflection coil for said cathode ray tube, said deriving and supplying means including a tuned flyback transformer producing flyback pulses; a voltage controlled oscillator; means for deriving an error signal indicative of a change in EHT both above and below a predetermined magnitude; means supplying said error signal to said voltage controlled oscillator to decrease the frequency of the output signal thereof in response to a decrease in EHT and to increase the frequency of the output signal thereof in response to an increase in EHT; and means utilizing said output signal to control the operation of said flyback transformer in such a way that the magnitude of said flyback pulses are increased in response to a decrease in EHT and decreased in response to an increase in EHT.