Abstract: A method and device utilizes a brightness control circuit for protecting a cathode ray tube in an image displaying device. The displaying device has an image signal amplifier, a cathode ray tube, and a brightness control circuit. The cathode ray tube has a screen, an electron gun, and an anode for collecting an electron beam emitted onto the screen to produce an anode current. The brightness control circuit is electrically connected to a control end of the image signal amplifier for controlling the amplification magnitude of the image signal amplifier and electrically connected with the anode of the cathode ray tube via a flyback transformer, wherein when the incoming image signals make the image picture shown on the screen too bright, the anode current of the anode will be increased accordingly, and the brightness control circuit will reduce the amplification magnitude of the image signal amplifier at the same time according to the increase of the anode current so as to reduce the anode current.

Abstract: A circuitry for attaining a fixed raster vertical scan size of a video display apparatus is proposed. The video display apparatus comprises a flyback transformer (FBT) which includes a primary winding and a secondary winding. The secondary winding has a terminal generating a high voltage to an anode of a cathode ray tube (CRT) of the video display apparatus via an external loading. Moreover, the secondary winding has a voltage reference terminal. The raster vertical scan size adjustment circuit comprises a compensation circuit and a raster vertical scan size control circuit. The compensation circuit includes an input terminal adapted to connect the voltage reference terminal of the secondary winding for detecting voltage change at the voltage reference terminal responsive to variation of the external loading. The compensation circuit has an output terminal generating the compensated signal.

Abstract: An apparatus for reducing the leakage of the magnetic field from a deflection yoke without consumption of additional energy is provided. The apparatus includes a first circuit and a second circuit. The first circuit substantially loops around the upper portion of the funnel shaped C.R.T., defining a first space, and is connected to the ground reference. When the upper magnetic field generated from the deflection yoke passes through the first space, a first current of eddy current type is generated within the first circuit which, in turn, results in heat whereby the leakage of the magnetic field is reduced. The second circuit substantially loops around the lower portion of the funnel shaped C.R.T., defining a second space, and is connected to the ground reference.