| 摘要 |
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. The raster vertical scan size control circuit, responsive to the compensated signal, adjusts the raster vertical scan size of the video displayed on the CRT such that the raster vertical scan size is substantially maintained.
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