Daewoo DWP-28W2ZZF Service Manual download pdf (Page 58)

Appendix Service manual WP-795

- 31 -

2-6 Sound amplification

The TDA8944J (TDA8946J) is a stereo BTL audio amplifier capable of delivering 2 x 7 W (2 x 15 W)

output power to an 8

Ω

load at THD = 10%, using a 12 V power supply and an external heatsink. The

voltage gain is fixed at 32dB.

With the three-level MODE input the device can be switched from ‘standby’ to ‘mute’ and to ‘operating’

mode.

The TDA 8944J outputs are protected by an internal thermal shutdown protection mechanism and short-

circuit protection.

Power amplifier

The power amplifier is a Bridge Tied Load (BTL) amplifier with an all-NPN output stage, capable of

delivering a peak output current of 1.5 A.

The BTL principle offers the following advantages :

- Lower peak value of the supply current.

- The ripple frequency on the supply voltage is twice the signal frequency.

- No DC-blocking capacitor

- Good low frequency performance

Mode selection

The TDA894xJ has several functional modes, which can be selected by applying the proper DC voltage to

pin MODE.

Mute : In this mode the amplifier is DC biased but not operational (no audio output). This allows the input

coupling capacitors to be charged to avoid pop-noise. The devices is in mute mode when 2.5 V < V

MODE

(Vcc-1.5 V).

Operating : In this mode the amplifier is operating normally. The operating mode is activated at V

MODE

0.5 V.

2-7 Vertical deflection

The vertical driver circuit is a bridge configuration. The deflection coil is connected between the output

amplifiers, which are driven in phase opposition. The differential input circuit is voltage driven. The input

circuit is especially intended for direct connection to driver circuits which deliver symmetrical current

signals, but is also suitable for asymmetrical currents. The output current of these devices is converted to

voltages at the input pins via resistors R350 and R351. The differential input voltage is compared with the

output current through the deflection coils measured as voltage across R302, which provides internal

feedback information. The voltage across R302 is proportional to the output current.

Flyback voltage

The flyback voltage is determined by an additional supply voltage V

flb

. The principle of operation with

two supply voltages (class G) makes it possible to fix the supply voltage Vp optimum for the scan voltage

and the second supply voltage V

flb

optimum for the flyback voltage. Using this method, very high

efficiency is achieved. The supply voltage V

flb

is almost totally available as flyback voltage across the coil,

this being possible due to the absence of a coupling capacitor.

Protection

The output circuit has protection circuits for :

- Too high die temperature

- overvoltage of output stage A

Guard circuit

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Daewoo DWP-28W2ZZF Service Manual Page 58

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