1997 Aug 27

10

Philips Semiconductors

Preliminary specification

Video output amplifier

TDA6120Q

Fig.7 Output (pins 12 and 13; falling edge) as a function of input signal.

162.5

150

100

50

37.5

38.75

36.25

overshoot (in %)

t

t

0

x

x

MGK445

Voc

Vi

tpd

tst

to(r)

FLASHOVER PROTECTION

The TDA6120Q does NOT include protection diodes that

clamp the cathode output pin to the high voltage supply pin

during a CRT flashover discharge. Therefore an external

high voltage reverse biased diode has to be connected

carbon high-voltage resistor in combination with a 2 kV

spark gap between the cathode and ground will limit the

maximum clamp current (for this resistor value, the CRT

has to be connected to the main printed-circuit board).

This external network causes an increase in the rise and

fall times and a decrease in the overshoot.

Pin 10 must be decoupled to pin 8:

• By a capacitor >22 nF with good HF behaviour (e.g. foil).

This capacitor must be placed as close as possible to

pin 10 and pin 8; definitely within 5 mm.

• By a capacitor >3.3 µF on the picture tube base printed

circuit board (common for three output stages).