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Blanking Driver and CRT Protection Circuit

IP.com Disclosure Number: IPCOM000094758D
Original Publication Date: 1965-May-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Olson, RE: AUTHOR

Abstract

In many instances it is necessary to provide various voltage levels to the cathode of a cathode ray tube (CRT). This is in order to permit normal operation, selective blanking of the beam and absolute cutoff of the beam for protection purposes.

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Blanking Driver and CRT Protection Circuit

In many instances it is necessary to provide various voltage levels to the cathode of a cathode ray tube (CRT). This is in order to permit normal operation, selective blanking of the beam and absolute cutoff of the beam for protection purposes.

Under normal operation of the CRT, zero and minus six volt signals are applied to the bases of transistors T1 and T3, respectively. This causes T1 to turn on and T3 is held off. With T3 held off, the base of T2 is at a positive voltage level and T2 is on. Therefore, with both T1 and T2 on, the output terminal 10 connected to the collector of T2 is at ground potential, or zero volts. Output terminal 10 connects with the cathode of the CRT, not shown.

When the beam of the CRT is to be blanked, minus six volts is applied to the base of T1 to turn it off. The minus six volts applied to the base of T3 is maintained. Hence, T3 is also off and, therefore, only T2 conducts. This places point 20 at approximately eleven volts. Thus, terminal 10 is at eleven volts.

In order to insure absolute cutoff of the beam so as to prevent burning the face of the CRT in the absence of deflection signals, a voltage of approximately plus one hundred volts is applied to the cathode of the CRT. To activate the CRT protection circuit, a zero volt signal is applied to the base of T3 to turn it on. With T3 on, T2 turns off. Consequently, the voltage at 10 goes to approximately plus one hundred volts as determi...