United Technologies Corporation

Michael H Kalmanash

Glenn C Waehner

Edward L Young

A high voltage color switch for a beam penetration CRT includes a constant current driver which provides a bias current to the high voltage transformer in the first color write period when the baseline color is being displayed. One or more secondary colors can be displayed during a second color write period during which a switch connects the transformer to a conventional voltage driver that provides the needed voltage swing. At the end of a secondary color write period the constant current driver is again connected to reset the flux level in the transformer to one end of its dynamic range. During a core reset interval only a small voltage offset appears on the anode of the CRT so that color information written in the baseline color appears without any perceivable change to a viewer. At the end of the core reset period the constant current source continues to supply a constant bias current to the primary winding of the transformer to maintain the flux level at one end of its dynamic range.

Constant current bias color switch for a beam penetration CRT

A high voltage color switch for a beam penetration CRT is well suited to generating a color write in one or more random colors during the retrace interval of a TV raster scan, or the like. The scanning period of the TV raster is in the baseline color for maximum resolution and brightness. A driver connected to the high voltage transformer includes a low voltage power supply which has one portion controlled by a switch. During the color write period the switch is closed so that the driver can provide a suitable waveform to the transformer to obtain the required swing. During the raster scan, the switch is open so that the magnetizing current in the transformer can be reset over the entire TV raster scan interval causing only a slight offset in the baseline color.

Stroke during retrace color switch

A color switch for a beam penetration CRT can display a randomly selected color in a first color write period, and immediately after the first color write period the magnetizing current in the high voltage transformer is reset during a second write period in a complementary color. A high voltage power supply has an output voltage selected to provide a baseline color whose voltage level is intermediate the voltage range of the CRT anode. A pair of drivers are connected to either end of the primary winding of the high voltage transformer and generate a voltage differentially across the primary winding that drives the voltage level either upwardly or downwardly from the baseline level. Immediately after the first color write period, a second color write period is formed in a complementary color by transitioning a pair of input switches. This causes the color switch to change to the voltage level on the opposite side of the baseline voltage level so that the flux level in the core of the transformer is reset to a balanced DC condition.

Differential random color switch for beam penetration CRT

A color switch for a beam penetration CRT includes a return path through a pair of reverse biased diodes to recapture a substantial amount of the energy associated with changing the voltage on the anode of the CRT for a write period in a non-baseline color. A driver circuit, which includes the low voltage power supply, is connected through a switch to one end of the primary winding of a transformer. The primary winding is also connected through one of two diodes to each half of the low voltage power supply for the driver. By opening the switch at the end of a color write period in a non-baseline color, the rapid decrease in the current through the primary winding of the transformer to restore DC balance of the magnetizing current in the transformer core forms a reverse voltage which is returned to the low voltage power supply through the diodes. The baseline color is selected to be in an intermediate range so that the anode voltage level can be swung in either direction so that a random non-baseline color can be selected for a color write period.

Random color switch for beam penetration CRT

A high voltage color switch for beam penetration CRT has two operating modes, the first of which is well suited to displaying a sequential group of colors on the faceplate of a CRT, and the second mode of which is well suited to displaying a random color that varies from a preselected baseline color. A high voltage power supply has an output voltage level which is selected to provide a predetermined baseline color when presented through the secondary winding of a transformer to the anode of a CRT. The primary winding of the transformer is connected through a first switch to the output of a driver. A feedback loop from the output of the driver senses the DC voltage level associated with the input waveform and biases the input of the driver to force the level of DC voltage presented to the primary winding of the transformer to zero. At the same time in the first mode the second switch is open so that the input waveform to the driver circuit is integrated in a low-pass filter into a DC level and then presented to the reference input of the high voltage power supply. In response to changes on its reference input the high voltage power supply changes its output voltage level so that no perceivable change is apparent to a viewer. In its second mode, the color switch can provide a color write period in a random color and the second switch is closed so that the high voltage power supply does not respond to changes in the DC level of the input voltage waveform. In this mode a reset period is necessary so that the magnetizing current in the transformer is returned to the center of its dynamic range.

Dual mode color switch for beam penetration CRT

An improved sequential color switch for a beam penetration CRT includes a high voltage power supply and a high voltage transformer. A feedback circuit senses the DC level in the signal waveform applied to the transformer and feeds it back to the input of a driver. A low-pass filter connected to the input of the driver also senses the DC level in the signal waveform applied to the driver and adjusts the reference input of the high voltage power supply to correspondingly change its DC high voltage output level. Essentially, this removes any DC level from the primary winding of the high voltage transformer while at the same time adjusting the output level of the high voltage power supply connected to the secondary winding of the transformer by an amount which is proportional to the average DC level of the input signal waveform.

Sequential color switch for beam penetration CRT

A regulated current source including a large inductance provides desired, average DC current by modulation of an electron switch, such that the inductance is disconnected from the power supply on a regular basis by a clock circuit, and the switch reconnects the power supply when the current in a return path to the inductor has decayed to a desired magnitude. The desired decay current across a resistor is compared with a reference which turns the switch on in the absence of the turn-off signal from a clock. As an energy saving adjunct in a deflection amplifier system for a CRT, a bipolar embodiment employing a single large inductance and duplicate other apparatus provides a regulated current of either polarity or zero magnitude, the inductor current being maintained even when providing zero current with the deflection system.

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Fairfield, CT, United States of America

Michael H Kalmanash