Toshiba TN50X81, TN55X71, TN55X81, TN61X81, TN40X81 User Manual

...

TOSHIBA Service Training

PROJECTION

TELEVISIONS

Main Power Supply

NTDMOD05

& Complete

Shutdown Guide

TN50X81 TN55X71 TN55X81 TN61X81

TN40X81 TW56X81 TW65X81

Contents

Overall Block Diagram.........5

Overall Block Diagram ..................................................................................... 6

Main Power Supply ..............7

Main Power Supply ........................................................................................... 8

VIN Terminal (pin 5) - Start Circuit ................................................................... 9

OCP/INH Terminal (pin 4) Function ................................................................. 9

Soft Start ........................................................................................................... 1 0

Surge Protect. .................................................................................................. 11

Oscillator/Constant Voltage Control Circuit ................................................ 12

Latch Block ...................................................................................................... 13

Overheat Protection Block (Internal to Q801)............................................. 13

Overvoltage Protection Block (Pin 5) ........................................................... 13

Latch Trigger Terminal (Pin 7)....................................................................... 1 3

Troubleshooting Flowchart ........................................................................... 14

Sub Power Supply..............1 5

Operation .......................................................................................................... 16

Start-up and Over Voltage Protect ................................................................ 17

Logic and Drivers............................................................................................ 18

Oscillator .......................................................................................................... 18

Oscillator Control ............................................................................................ 19

Latch ................................................................................................................. 19

Thermal Shock Detection Block ................................................................... 2 0

Over Current Protection................................................................................. 20

Soft Start ........................................................................................................... 2 0

Resonance Correction ................................................................................... 21

Additional Information .................................................................................... 22

Troubleshooting Flowcharts ......................................................................... 23

Shutdown ......................................................................................................... 25

Basic Operation............................................................................................... 26

Monitoring Circuits ......................................................................................... 28

X-Ray Protection ............................................................................................. 28

+128V Over Current Protect .......................................................................... 29

+128V Over Voltage Protect ........................................................................... 3 0

Horizontal Stop Protection Circuit ................................................................ 31

+21V Over Voltage Protect ............................................................................. 32

+35V Over Current Protect ............................................................................ 3 3

+21V Over Current Protect ............................................................................ 3 4

-21V Over Current Protection ........................................................................ 35

+200V Low Voltage Protect ............................................................................ 36

Troubleshooting Flowchart ........................................................................... 37

Overall Block Diagram

Troubleshooting Tip:

Figure 1 is an overall block diagram of the standby , main, and sub power supplies in the progressive scan televisions. The standby supply is always active whenever the television is plugged into an AC line source. It delivers 5V VDD and a reset 5V to the microprocessor to keep it operational at all times, even when the television is OFF . Transformer T840 isolates the standby supply from the live ground, and D840 is a full-wave bridge rectifier that supplies 15V DC to voltage regulator Q840 and relays SR81 and SR83 (relay connections not shown). When the microprocessor receives an ON command from the remote control or power key on the front of the television, it sends 5V to the relay drivers to close relays SR81 and SR83. Closing the relays supplies the AC line input to the remaining two power supplies to operate the television.

Standby Supply

Standby

Regulator

Q840

5V=Relay On 0V=Relay Off

Q841

Relay

Q842

Drivers

5V=Relay On 0V=Relay Off

Relay

Drivers

Sub-Power Supply

Q844 Q843

SR83

Relay

+5-1

Microprocessor

VDD

Reset

QA01

Rectifier

D801

Main Switching IC

Rectifier

D861

AC Line Input

Rectifier &

Isolation Trans.

D840 T840

SR81 Relay

F811

F860

If both relays never close, check the standby power supply . Both the 5V VDD and the reset 5V are mandatory for the microprocessor to operate.

The main power supply and sub power supply work independently from each other, so one supply can be disabled to check the other. If the main power supply is disabled, the television would not have picture or sound, but the microprocessor would still control the relays. Therefore, the sub supply could be turned ON and OFF and its voltages would appear as normal. If the sub power supply is disabled, everything would work except the picture would be out of convergence. Either power supply can easily be disabled by removing its fuse: F860 for the sub supply and F811 for the main supply .

Main Power Supply

140V

Q801

Feedback

Main Switching IC

140V

Q888

Feedback

Photo

Coupler

QB03

Photo

Coupler

Q861

T861

21 20

D812

D810

D809

14 15

D808

Amp.

D887

T888

D888

13 12

Amp.

D811

D813

Error

D891 D895

Error

+7V

+35V

+15V

+11V

+128V

Q804

36.5V

21V

-21V

Q863

Figure 1. Overall Block Diagram

Main Power Supply

Photo

Coupler

Error

Amp

O S C

T861

Q801

QB03

Q804

128V

140V dc

From D801

D808

The main power supply is a ringing choke converter. Figure 2 is a block diagram for this supply . An oscillator (OSC) and a switching MOSFET are internal to the main switching IC, Q801. During normal operation, D801 rectifies the AC line input to approximately 140V . This voltage is applied to the MOSFET through transformer T861’s primary winding. As shown in Figure 3a, when the MOSFET conducts, current flows through T861’s primary windings and builds an electromagnetic field. Figure 3b demonstrates that after the field builds, the MOSFET opens to stop the current flow through T861. This causes the electromagnetic field to collapse and induce current into the secondary windings.

Figure 2. Main Power Supply Block Diagram

When the MOSFET conducts,

current flows through T862,...

140V dc

From D801

Q801

O S C

When the MOSFET Stops conducting,

the electromagnetic field collapses...

T861

140V dc

From D801

Q801

T861

128V

D808

...and an electromagnetic

field builds.

S C

Error

Amp

Photo

Coupler

Q804

Coupler

QB03

Electromagnetic Field

Current Flow

(a) (b)

Figure 3. Main Power Supply Operation

128V

D808

...and current is induced in

the secondary windings.

Error

Amp

Photo

Q804

QB03

VIN Terminal (pin 5) - Start Circuit

0.5V

Drive Output

OCP/INH terminal

voltage

As shown in Figure 4, pin 5 (VIN) of Q801 is the Startup and Over V oltage Protect (OVP) for Q801. To start the operation of the power supply, 140V draws current through resistors R802 and R803 which builds a charge on capacitor C825. When the charge reaches 22.5V, Q801 starts switching. Once Q801 is operating normally , the N ode D805 provide 25V to pin 5 to maintain Q801’s switching operation. At this time, C825 functions as a filter capacitor. Pin 5 is also the over voltage protection (OVP). If the voltage on V

raises above 28V , an internal latch

stops Q801 from operating. Refer to the Latch section for further details.

winding and rectifier di-

(2) INH Function (OFF Time Control)

At the same time the OCP comparator turns the MOSFET OFF , the inhibit (INH) comparator stops the oscillator and prevents the MOSFET and oscillator from operating until the OCP voltage drops below 0.5V . The waveforms for this operation are shown in Figure 6.

Q801

To T861

Drive

R803 & R802

From D801

25V dc

D806

5 V

D805

R825

C825

T861

Q801

OVP

Start

Figure 4. VIN T erminal and Start Circuit

OCP/INH Terminal (pin 4) Function

The OCP/INH terminal is a safety terminal that protects Q801 if an over current condition develops during operation. Figure 5 shows this circuit diagram.

OCP

Latch

0.5V

INH

Oscillator

0.5V

Figure 5.

Over Current Protect (OCP)

and Inhibit (INH) T erminal

R807

R827 R828

(1) OCP Function (Over Current Protect)

When the MOSFET is turned ON, current flows through resistors R827 and R828 and a voltage develops at the over current protect (OCP) terminal at pin 4. If the voltage reaches 0.5V, the internal OCP comparator turns the MOSFET OFF and stops its current flow .

Figure 6.

OCP/INH W aveforms

Soft Start

Without Soft Start

With Soft Start

The soft start circuit prolongs the life of the power supply by reducing surge current at Turn on. Figure 7 shows the soft start circuit. When the power supply starts up, a regulator inside Q801 outputs 3.1V on the soft start terminal pin 7 that causes current flow through the over current protect (OCP) resistors (R827 and R828) and resistor R811. The additional current flow makes the OCP more sensitive. The increased sensitivity causes the OCP to trigger earlier than normal which reduces current through the MOSFET and T861’s primary windings. Once C818 is fully charged, current stops flowing through the OCP resistors and normal operation begins. Figure 8 shows the effect the soft start circuit has on the MOSFET’ s drain current during startup.

Q801

To T861

Drive

R807

Over Current Protect

C818

Latch Trigger

3.1V

Figure 7. Soft Start Figure 8. Soft Start Effect

R811

R827

R828

Surge Protect.

Refer to figure 9. R815 and R816 reduce surge current through the main power supply at startup. They provide additional resistance on the ground path of rectifier D801. Relay SR85 and SR81 are disengaged before the supply operates. When relay SR81 closes, AC current is applied to rectifier D801. After the supply begins to operate, it produces voltage sources on the secondary of T861. T wo of the voltage outputs engage SR85. The 15V output supplies a current source for SR85. The 7V source forward biases Q805 to close the relay and provide a direct ground path for D801 by bypassing R815 and R816.

Main Power Supply

Relay SR81

R815

R816

Q801

D801

and

T861

SR85

Figure 9. Surge Protect

15V

R832

R826

D823

Q805

Oscillator/Constant Voltage Control

Circuit

Refer to Figure 10. Internal to Q801 is an oscillator and oscillator control circuit. The oscillator controls the switching MOSFET in Q801. To control the power supply’s regulation, a feedback signal manipulates the oscillator frequency to maintain a consistent current flow through the load. Internal to Q801, Capacitors C2 and C3 and resistor R3 and R2 determine the MOSFET’ s base switching frequency . The MOSFET’s OFF time is a fixed value determined by R3 in parallel with C3. C2 and R2 determine the maximum duration of the MOSFET’s ON time. An external pulse width modu-

lated (PWM) control signal, developed by any variance in the load current and coupled to the power supply’s primary side by a photo-coupler , is applied to the feedback (F/B) of Q801 on pin 6 to adjust the charging time of C2 as required by the load. If the load voltage decreases, the MOSFET’s ON time increases to compensate and increase the output of the power supply . The longer the ON time, the larger the electromagnetic field builds around T861’s primary windings. The larger electromagnetic field induces more current into the secondary windings when it collapses. On the other hand, if the load voltage increases, the ON time decreases to reduce the overall output of the power supply .

From Start Block

Regulator

Latch

Q801

Drive

Oscillator

OCP

To 25V VIN

F/B

R813

R814

128V Main B+

R817

R819

Q803

R818

Q804

Figure 10. V oltage Control

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