LA7837 データシートの表示（PDF） - SANYO -> Panasonic

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LA7837

Vertical Deflection Circuit with TV/CRT Display Drive

SANYO -> Panasonic 

LA7837, 7838

Precautions when using with display having short retrace time :

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 as shown in Fig.3 will cause pin 6 waveform start

wave to become linear, so that stretching is suppressed. The example of circuit application shown in Fig.3 does not

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.

Fig. 4

Design Example

For 12V pin 1 power supply

On the LA7837, 7838, pin 3 one-shot multivibrator operates when a trigger pulse enters pin 2. During this time, the

sawtooth wave generator discharge circuit and clamp circuit inside pin 6 operate.

The clamp voltage at this time is figured according to this formula :

VCLAMP=5/12 · VCC ........................... ¡

For 12V,

VCLAMP=5 [V]

Therefore, the Zener diode used in Fig.3 must be rated more than 5V (e.g. 5.6V), otherwise the clamp circuit inside

the IC will operate.

For 9V pin 1 power supply

The same as for 12V, according to formula ¡ :

VCLAMP=3.75 [V]

So, that Zener diode must be rated more than 4V (e.g. 4.5V).

No.3313–6/9

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