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Amplitude Regulation of a Sine Wave Deflection System by Pulse Width Modulation

IP.com Disclosure Number: IPCOM000075388D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Katsafouros, SG: AUTHOR

Abstract

In a deflection system utilizing sinusoidal rather than ramp signals for deflection in a cathode-ray tube display, a highly regulated power supply is normally required due to the direct dependence of the amplitude of the sinusoidal deflection signal on the power supply voltage. The yoke current and, therefore, the picture size on the face of the CRT is directly proportional to the power supply voltage, and power supply variations tend to shrink or enlarge the picture size. A circuit configuration to regulate the amplitude of the deflection signal as a function of the yoke current, rather than regulate the power supply, provides an alternative solution of this problem.

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Amplitude Regulation of a Sine Wave Deflection System by Pulse Width Modulation

In a deflection system utilizing sinusoidal rather than ramp signals for deflection in a cathode-ray tube display, a highly regulated power supply is normally required due to the direct dependence of the amplitude of the sinusoidal deflection signal on the power supply voltage. The yoke current and, therefore, the picture size on the face of the CRT is directly proportional to the power supply voltage, and power supply variations tend to shrink or enlarge the picture size. A circuit configuration to regulate the amplitude of the deflection signal as a function of the yoke current, rather than regulate the power supply, provides an alternative solution of this problem.

Referring to the drawings, a constant-frequency constant-amplitude signal such as shown in waveform (a) is applied from terminal 1 to the base 3 of transistor T1. Positive transitions of the input signal cause the collector 5 of transistor T1 to go negative. This negative transition is coupled through capacitor 7, terminal 9 and diode 10 to the base of transistor T2, causing transistor T2 to turn off and the collector of T2 and terminal 11 to go positive. The collector will stay positive until capacitor 7 recharges, at which time the collector of transistor T2 will go negative producing the waveform (b). Under normal operating conditions, i.e., no variation in the power supply voltage, a pulse of duration tN shown as the...