| 摘要 |
1,010,630. Television; cathode-ray tube circuits. TELEFUNKEN PATENTVERWALTUNGS GESELLSCHAFT. June 29, 1964 [June 29, 1963], No. 26763/64. Headings H4F and H4T. In a circuit arrangement which increases the slope of a cathode-ray tube by having a relatively low bias potential at the second control electrode and in which the video signal varies the potential of the cathode of the tube relative to the potential of the two control electrodes in the same sense, both electrodes causing picture modulation, the picture brightness control is arranged to adjust concomitantly the biases in the same sense applied to the control electrodes. As shown, Fig. 1, a cathode-ray tube 1 of a television receiver has its first control electrode G1 connected to the sliding contact 3 of a potential divider 4, 5. The video signal 18 is fed to the base of amplifying transistor 8 from the collector of which it is applied to the cathode 11 of the tube. Potential divider 13, 14 having a permanently set tapping point 15 derives the bias potential for the second control electrode G2, and the resistance between the tapping point 15 and the sliding contact 3 is low compared with the total resistance of the divider 13, 14 owing to the high operating voltage of 500 v. In operation the sliding contact 3 is moved to change the brightness of the tube and as the potential divider 4, 5 is of low resistance compared with divider 13, 14 the percentage of the current flowing through 4, 5 which flows through 13, 14 changes only slightly, so that the potential difference between the control electrodes G1 and G2 remains almost unaltered, Fig. 2, not shown. Potential divider 2, 12 which adjusts the base bias potential of transistor 8 may replace the divider 4, 5. In a further embodiment, Fig. 3, contrast regulation is achieved employing a sliding contact 16 of a potential divider 17 which is connected in parallel with the load resistor 9, and owing to the fact that the upper end of the divider 4, 5 is connected to the cathode 11 and follows the potential fluctuations of the cathode, and the electrodes G1, G2 are coupled together in accordance with Fig. 1, the potentials at the electrodes G1 and G2 vary at the same rate as the potential at the cathode 11. The sliding contact of resistance 19 is used for the setting of the focusing potential for the tube. |
