LA7837 Просмотр технического описания (PDF) - SANYO -> Panasonic

Номер в каталоге

Компоненты Описание

производитель

LA7837

Vertical Deflection Circuit with TV/CRT Display Drive

SANYO -> Panasonic 

LA7837, 7838

LA7837, 7838 application in a multi-sync system

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).

Countermeasure 1

In order to stabilize vertical size change, an

operational amplifier is used to change the

circuit to one which controls pin 4 vertical

size control current.

Voltage which corresponds to vertical fre-

quency changes is applied to the operational

amplifier to stabilize vertical size.

Fig. 8

The other problem is that vertical linearity chages when used at multi-frequency (e.g. 40 to 80Hz).

The reason for this is that R5 and C1 time constants are used for linearity correction (Fig.9), so even though the value

is optimum for a certain frequency, it is not for others.

Countermeasure 2

As shown in Fig.10, good linearity can be obtained by setting frequency ranges of use for R5 and C1 time constants for

vertical linearity correction, and switching them.

For example :

40 to 60Hz Switch A

60 to 80Hz Switch B

For switch A, R5 and C1 are set so that vertical linearity response is optimum for fv≈50Hz.

Next, for switch B, R5’ and C1’ are set for optimum value at fv≈70Hz.

By dividing the vertical trigger pulse range (e.g.40 to 80Hz) and performing linearity correction in this way, linearity

distortion can be kept below about 3%.

No.3313–8/9

Share Link: