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Sharp Electronics (UK) Ltd

Technical Support

February 99

Page 29

Sharp Electronics (UK) Ltd

Technical Support

February 99

Page 30

The principles of all the audio output stages, including the sub-woofer are the same. And the principle
of operation is the same, as the vertical output stage except the frequency of the PWM single will vary
depending on the audio being inputted to the circuit.

The base frequency of the PWM is much higher than that which is used for the field output stage due
to harmonics that could be heard by pets. And it will increase by as much as 20kHz (audio bandwidth)

The oscillator used to produce this changing frequency is a 'triangle wave oscillator', and the key
components are R352 & C330.

The time that it takes C330 to charge will determine the frequency of the oscillator. To enable this
oscillator to change frequency; the charging voltage is derived from the input to the low pass filter
(L302) shown in Figure 2, fed back via R329. R352 will determine the time the C330 takes to
discharge.

+

-

Audio I/P

Q302

Q301

R320

R354

C342

R350

R321

R325

R322

R326

R334

R324

D333
C4V7

C335

D322
C4V7

D323
C4V7

C358

C347

R349

D335

D334

R328

R329

C330

R352

C383

IC303

+19V

-19V

Sharp Electronics (UK) Ltd

Technical Support

February 99

Page 31

R330

R333

Q304

R331

R354

Q303

Q318

D331

Mute

C359

D309

D302
C18V

D301
C18V

C331

C332

C352

D326

C381

D327

R382

C359

Q305

Q306

D306

C344

C388

C387

D305

C343

-19V

L302

C333

Protection

+19V

Wide Screen, Colour Television   CW100 Chassis

Sharp Electronics (UK) Ltd

Technical Support

February 99

Page 32