| 摘要 |
PURPOSE:To prevent the radiation of X-rays and also to prevent an abnormal rise of a heater voltage by detecting the voltage produced by the variation of a beam current to supply this voltage to a switching transistor and threrefore reducing the level of the anode voltage when the beam current has a high level. CONSTITUTION:The output of an IC1 for processing of signals of a deflecting circuit is supplied to an anode of a CRT via an X-ray protecting circuit. For this protecting circuit, a bias is applied to a point P from a power supply 3 via a resistance R14 and the potential difference between both terminals of a capacitor C3 increases as a beam current increases. Thus the voltage is reduced from a prescried level at the point P. When the beam current increases more, the potential of the point P is reduced gradually. Then a diode D4 and a switching transistor TR2 conduct and an R10 is set in parallel to an R12. Thus the horizontal oscillation frequency is forcibly held at a high level. Therefore the anode voltage is reduced less than a level at which the X-rays are possibly radiated. |
