LA76931 データシートの表示（PDF） - Unspecified

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LA76931

64Pin LA76931 for Color Television Receiver / SERVICE MANUAL

Unspecified 

R511

+ 300V

R520

V511

R521

R522

3

R525

T511

9

C516

7

VD551

R555

C551

+

C561

R554

5

N501

+B1

112V

V553

C

B

R552

N501

VD 514

C514

VD 517

R524

Ib Ic

Ie

R519

V513

C517

1

R556

6.2V E

VD 561

RP 551

R553

V512

300V -

2

Diagram 2

In the circuit of LA 76931 series, the main output voltage is 112V . The safety of the television will be effected while the voltage was changed So we

must adopt regulative circuit to ensure the stabilization of the output voltage.

When V513 is on , the current flows through pin3 and pin7 of T511, then be converted magnetic energy to be stored. The magnetic energy s

strength corresponds with the V513 s condition . The switch on time more longer , the energy magnetic stored in T511 will be more stronger. The inducted

voltage (pin10 - pin16) will be more higher. On the contrary condition , it just reverse. So the output will be controlled only via controlling the on/off time of the

switch transistor.

Regulator is based on the above theory. We can use V512 to bypass the current flowing into base of V513 in order to control the on-off time of V513.

The switchmode power supply automatic regulates the current in the base of switch transistor to keep the out stable. By diagram2, let us analyse the regulation

process.

R552,RP 551, R553 connect in series. The sample voltage is taken from RP 551. Obviously, the voltage directly reflects the variety of +B . If the

Voltage of +B is high ,the voltage on the base of V513 is high. If the voltage of +B is low, the voltage on the base of V513 is low. At the same time

+B offers the breakdown current on VD 561 through R554 to keep 6.2V on the emitter of V553. So Vbe vary with +B . The error current that flow

across b-e of V553 is determined by +B . +B also add VD 515 through R555,R556 and produce the current flowing back to the collector of V553.

N501 is an photocoupler that implements light - electric conversion. By this photocoupler , first the +B error is converted into light error, then the light

error is converted into resistant error. The final voltage regulated depends on V511,V512 etc. The resistant error just reflect s the +B error. It is

connected with the base of V511 and controls the degree that V511 turns on. This will cause the current variety in the collector of V511, this various

current is amplified by V512 and controls the b-e current in of V513 (Ib). So the working condition of V513 can be controlled.

The flow chart is as follows:

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