| 摘要 |
The present invention relates to a vertical deflection circuit of a picture display unit which is capable of displaying pictures against variety of scanning frequencies. There are provided: a vertical oscillation means which generates a deflection voltage (VSAW) synchronizing with a vertical synchronizing signal (VD), includes a constant current source and is capable of varying the amplitude value of said deflection voltage (VSAW) by varying the current value of said constant current source; a vertical drive means which obtains a drive signal from the deflection voltage from said vertical oscillation means; a vertical output means which applies a vertical deflection current to a vertical deflecting coil based on the drive signal from said vertical drive means; an amplitude detecting means which detects the maximum amplitude value of a vertical deflection current (Vs) applied to said vertical deflecting coil; a comparison means which compares the maximum amplitude value detected by said amplitude detecting means with a reference value which is set by a setting means; and a control means which controls the current value of the constant current source in said vertical oscillation means based on the result of comparison by said comparison means; and in said amplitude detecting means, it is arranged, when the maximum amplitude value of the vertical deflection current is detected, to renew the detected maximum amplitude value, for example, in every vertical period. With this, there is provided a vertical deflection circuit of a picture display unit in which it is possible to maintain the display size in the vertical direction of the picture shown on the scope always constant even if the vertical scanning frequency is varied and also to change above said display size to an optional size, and furthermore, said display size is not varied with element dispersion, temperature characteristic, power source voltage fluctuation and so forth in the vertical drive circuit, the vertical output circuit, the vertical deflecting coil and the like as a primary factor, and good follow-up performance is also obtainable when abovementioned display size is varied.
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