5/9

TDA8145

Figure 6. Application Circuit with Keystone Correction

CIRCUIT OPERATION

(see the shematic diagram)

A differential amplifier OP1 is driven by a vertical

frequency sawtooth current of ± 33µA which is

produced via an external resistor fromthe saw-

tooth voltage. The non–inverting input of this am-

plifier is connected with a reference voltage

corresponding to the DC level of the sawtooth volt-

age. This DC voltage should be adjustable for the

keystone correction. The rectified output current of

this amplifier drives the parabola networkwhich

provides a parabolic output current.

This output current produces the corresponding

voltage due to the voltage drop across the external

resistor at pin 7.

If the input is overmodulated (> 40µA) the internal

current is limited to 40µA. This limitation can be

used for suppressing the parasitic parabolic cur-

rent generated during the flyback time of the frame

sawtooth.

A comparator OP2 is driven by the parabolic cur-

rent. The second input of the comparator is con-

nected with a horizontal frequency sawtooth

voltage the DC level of which can be changed by

the external circuitry for the adjustment of the pic-

ture width.

The horizontal frequency pulse–width modulated

output signal drives the final stage. It consists of a

class D push–pull output amplifier that drives, via

an external inductor, the diode modulator.

LM

5

TDA8145

R5

RT3

1k

Ω

Hfly

from L.T.

Keystone

Adj.

Line Transformer

(L.T.)

Pin 1

Voltage

H. Width

Pin-cushion

adjustment

L1

10mH

R3

RT2

4.7k

Ω

47k

Ω

7

2

1

3

4

8

6

C1

47nF

R4

18k

Ω

V

S

C2

100nF

D1

1N4148

C3

4.7nF

R2

12k

Ω

RT1

100k

Ω

R1 =

V

FRAME

66

µA

PP

V

FRAME