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Dynamic Load Correction for EHT Voltage Regulation

IP.com Disclosure Number: IPCOM000039303D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Hewett, SJ: AUTHOR [+2]

Abstract

In an EHT regulation system for a CRT display, a primary winding of an EHT transformer is driven by a pulse-width modulation circuit controlled by an error amplifier. A diode split secondary winding generates an EHT output voltage. An auxiliary transformer winding is used to generate a sense voltage which is fed back to the error amplifier. The EHT current is monitored by a resistor controlling a circuit whose output modifies the sense voltage to provide dynamic load correction. In a regulated EHT generation system the problem arises of reliably sensing EHT. This may be achieved by direct sensing of EHT using a dropper resistor, but high voltage resistors have wide tolerance, aging and drift characteristics and susceptibility to static discharges.

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Dynamic Load Correction for EHT Voltage Regulation

In an EHT regulation system for a CRT display, a primary winding of an EHT transformer is driven by a pulse-width modulation circuit controlled by an error amplifier. A diode split secondary winding generates an EHT output voltage. An auxiliary transformer winding is used to generate a sense voltage which is fed back to the error amplifier. The EHT current is monitored by a resistor controlling a circuit whose output modifies the sense voltage to provide dynamic load correction. In a regulated EHT generation system the problem arises of reliably sensing EHT. This may be achieved by direct sensing of EHT using a dropper resistor, but high voltage resistors have wide tolerance, aging and drift characteristics and susceptibility to static discharges. If the resistor includes focus and G2 potentiometers, then leakage of these grids can also cause errors. Also, a set-up potentiometer is required, and this causes problems to manufacturing because EHT must be measured. Alternatively, indirect sensing using an auxiliary secondary winding of the EHT transformer may be used. This overcomes most of the problems above except that changes in EHT due to EHT loading are not 'seen' by the sense voltage. The circuit disclosed dynamically loads the sense output according to EHT load so that the EHT load characteristics are simulated. In the circuit diagram, D1 and C2, driven by the auxiliary secondary winding AUX, provide the sense output. This is divided by R5 and R6 and fed to an error amplifier. A Pulse-Width Modulation (PWM) system then controls the sense voltage, and therefore the E...