Browse Prior Art Database

CRT Degauss for Wide Range Input Voltage Supply

IP.com Disclosure Number: IPCOM000062332D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Wood, JI: AUTHOR

Abstract

In a CRT color display, a degauss coil requires a high initial AC current for degaussing, decaying to a very low residual current. The circuit disclosed operates over a wide range of AC input voltage by using a thermistor (negative temperature coefficient) across the coil, a positor (positive temperature coefficient) in series with the coil, and a heater across the AC supply. As these three components are in thermal contact, a high initial current decays to a very low residual current as the temperature increases. The above diagram shows the circuit used. Across the degauss coil is thermistor R-, and positor R+ is in series with the coil. In parallel with this combination is heater RH. The AC input supply is connected across RH.

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CRT Degauss for Wide Range Input Voltage Supply

In a CRT color display, a degauss coil requires a high initial AC current for degaussing, decaying to a very low residual current. The circuit disclosed operates over a wide range of AC input voltage by using a thermistor (negative temperature coefficient) across the coil, a positor (positive temperature coefficient) in series with the coil, and a heater across the AC supply. As these three components are in thermal contact, a high initial current decays to a very low residual current as the temperature increases. The above diagram shows the circuit used. Across the degauss coil is thermistor R-, and positor R+ is in series with the coil. In parallel with this combination is heater RH. The AC input supply is connected across RH. The three resistive components R-, R+ and RH are in thermal contact within a suitable package and are arranged so that when the AC supply is switched on and RH increases in temperature, R- and R+ reach their final steady temperature in about two minutes. The circuit operates as follows. When the AC supply is switched on, positor R+ has a low resistance and a current of about 40 amps peak-to-peak flows through the degauss coil. As RH increases in temperature, R+ resistance increases and the coil current decays to a low value. Thermistor R- has initially a high resistance which reduces to a low resistance at final steady temperature to reduce the coil current to a very low value, i.e., a few m...