STV9556 datasheet(12/24 Pages) STMICROELECTRONICS

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STV9556

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10 APPLICATION HINTS

10.1

How to choose the high supply voltage value (VDD) in DC coupling mode

The VDD high supply voltage must be chosen carefully. It must be high enough to provide the necessary

video adjustment but set to minimum value to avoid unecessary power dissipation.

Example (see Figure 2):

The following example shows how the optimum VDD voltage value is determined:

– Cut-off adjustment range (B) : 25V

– Max contrast (D) : 40V

Case 1:

10V Brightness (C) adjusted by the preamplifier :

VDD =A+ B +C+D+E

VDD = 15V + 25V + 10V + 40V + 17V = 107V

Case 2:

10V Brightness (C) adjusted by the G1 anode:

VDD =A+ B +D+E

VDD =15V +25V +40V +17V = 97V

10.2

Arcing Protection: schematics

As the amplifier outputs are connected to the CRT cathodes, special attention must be given to protect

them against possible arcing inside the CRT.

Protection must be considered when starting the design of the video CRT board. It should always be

implemented before starting to adjust the dynamic video response of the system.

The arcing network that we recommend (see Figure 16) provides efficient protection without deteriorating

the amplifier video performances.

The total resistance between the amplifier and the CRT cathode (R10+R11) protects the device against

overvoltages. We recommend to use R10+R11 > 200

Ω.

Spark gaps are strongly recommended for arcing protection.

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