Description
The LA7837, 7838 are vertical deflection output ICs developed for use in high-grade TVs and displays. The interlace and crossover distortion responses, in particular, have been greatly improved, allowing excellent picture quality on large size televisions and high precision interlace mode displays. Also, pulse signals can be used for input signals due to the on-chip sawtooth wave generating circuit and driver circuit. Further, the DC and AC feedback circuit can be formed with these ICs alone, simplifying pattern design of sets and ensuring stable performance. All of the functions in a color TV signal system can be processed by connecting these ICs with SANYO’s single-chip IC LA7670 series (NTSC) and LA7680/85 series (PAL/NTSC) (VIF/SIF, video, chroma, deflection).
The LA7837 has a maximum deflection current of 1.8App, making it appropriate for use in portable to mid-size televisions. The LA7838 has a miximum deflection current of 2.2App, so it can be used for large size sets, and can drive from 33 to 37 inches.
The vertical output ICs LA7837, 7838 are appropriate for use in monitors and displays because the interlace and crossover distortion responses are superior to those of the LA7835, 7836. However, since the vertical retrace time of displays is shorter than that of TV, the upper portion of the vertical picture may stretch. This is because the start waveform of the pin 6 sawtooth wave bends, as shown in Fig.4, due to the diode response of the clamp waveform. If there is not much time difference between T1 ant TR, the upper portion of the vertical picture will tend to stretch. The use of a circuit will cause pin 6 waveform start wave to become linear, so that stretching is suppressed. use the trigger input circuit (pin 2) and one-shot multivibrator (pin 3) built in the LA7837, 7838 ; the pin 6 sawtooth wave is controlled by the LA7855, 7856 vertical output pulse. Therefore, the discharge circuit and clamp circuit are formed by the external Zener diode and transistor TR2.
The LA7837, 7838 can also be used in a vertical frequency multi-sync system. The LA7837, 7838 do not have an on-chip vertical oscillation circuit, so they operate merely by impressing a trigger pulse (e.g. 40 to 80Hz) on pin 2. However, there are two problems with using the LA7837, 7838 as are in a multi-sync system. One is vertical amplitude. When the trigger pulse changes between 40 to 80Hz, the vertical frequency will rise and amplitude size decreases (because pin 6 cycle (T1, T2) in the diagram below becomes shorter).
The vertical output IC LA7837, 7838 are appropriate for use in monitors and displays because the interlace and crossover distortion responses are superior to those of the LA7835, 7836. However, since the vertical retrace time of displays is shorter than that of TV, the upper portion of the vertical picture may stretch. This is because the start waveform of the pin 6 sawtooth wave bends, due to the diode response of the clamp waveform. If there is not much time difference between T1 ant TR, the upper portion of the vertical picture will tend to stretch. The use of a circuit will cause pin 6 waveform start wave to become linear, so that stretching is suppressed.
Features :
- Low power dissipation due to on-chip pump-up circuit
- On-chip 50/60Hz vertical size control circuit
- On-chip sawtooth wave generating circuit
- On-chip driver circuit
- Vertical output circuit
- On-chip thermal protection circuit
- Excellent interlace response
- Excellent crossover response
Pinout Diagram
No comments:
Post a Comment