Hitachi 46W500 Training Download

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DP-3X SW +115V POWER SUPPLY REGULATION EXPLANATION

PAGE 01-13

Hi-Voltage Power Supply Circuit Diagram explanation:
(See Power Supply SW+115V Regulation Circuit Diagram for details)

THIS POWER SUPPLY RUNS ONLY WHEN THE SET IS TURNED ON:

TURNING ON THE SW +115V POWER SUPPLY:

When the Set is turned on, the Microprocessor

I001

Outputs a Power On/Off 1 high command via pin

. This

Power On command is routed through

Q027

and

Q028

to the

PPS4

connector pin

. This High will be passed to

the base of

Q902

provided the Shut Down sensor

Q904

isn’t activated. When the base of

Q902

goes high, it’s

collector will go low. This will supply a ground path for the power on Relay

S901

turning it on. When the relay is

energized, AC is supplied to the Bridge rectifier

D901

develops raw 150V which is routed through

F903

to Pins

and

T901

. This voltage is routed through

the primary coil inside

T901

and out pins

and

to pin

I901

which is the Drain of the internal Switch MOS

FET. The Ground return path for the primary voltage is out pin

I901

which is the Source of the internal

Switch MOS FET and then through four 0.22 ohm resistors

R908

R909

R910

and

R911

See SW+115V Regulation Circuit Diagram for details.

SW +115 REGULATION

SW +115V pulse is generated from pin

T901

. This pulse is rectified by

D925

, filtered by

C943

and then

routed through the Excessive Current sensing circuit

R944

and

Q905

The primary route for the

SW +115V

is through

E907

L923

to pin

and

PPD5

and output as

SW +115V

to the Deflection circuit and High Voltage generation circuit.
However, the regulation route is through

E906

to pin

I904

. Internally, the regulator transistor works as a

variable resistor whose resistance is dependant upon the

SW +115V

voltage fluctuations. The internal variable

resistor manipulates the current flow from pin

to pin

ground. This will cause the voltage at pin

I903

to be

manipulated. Internally, the LED is illuminated by degrees dependant upon the

SW +115V

voltage fluctuations.

The internal receiver receives this light and acts as a variable resistor from pin

to pin

which is the regulation

control signal.
This action causes pin

I901

to manipulate the internal oscillator within

I901

. This in turn causes the fre-

quency of the drive pulse delivered to the Gate of the internal SMOSFET (Switch Metal Oxide Semiconductor
Field Effect Transistor) to manipulate the frequency of the pulse generated on the primary of

T901

. The current

drain of the internal SMOSFET is monitored by four low ohm resistors mentioned above. If this current exceeds
a specific value, the voltage developed by these low ohm resistors is routed through

R912

back into pin

which

is the Over Current Protection circuit as well as the Regulation Control pin. This pin will inhibit the drive signal
to the gate of the SMOSFET. As soon as the excessive current situation is eliminated, the IC will recover and
continue functioning.

B+ GENERATION FOR THE POWER SUPPLY DRIVER IC:

Vcc for the Driver IC is first generated by the AC input. This voltage is called Start Up Voltage.

I901

requires

23.3V

DC to operate normal. However, it will begin operation at

12V DC

on pin

I901

When AC is applied to the main full wave bridge rectifier

D901

where it is converted to Raw 150V DC voltage

to be supplied to the power supply switching transformer

T901

and

However, one leg of the AC is routed to a half wave filter consisting of

R906

and

R907

(both a 3.9K ohm resis-

tor), filtered by

C911

, clamped by a 36V Zener

D911

and made available to pin

I901

as start up voltage.

When this voltage reaches 12Vdc, the internal Regulator of

I901

is turned On and begins operation.

When the power supply begins to operate by turning on and off the internal Switch MOS FET, the Raw 150V DC
routed through

T901

, in on pin

(Drain) and out on pin

which is the Source. The Source of the internal Switch

MOS FET is routed out of pin (

) through four low ohm resistors to hot ground. When the internal Switch MOS

FET turns on, it causes the transformer to saturate building up the magnet field. When the internal Switch MOS
FET turns off, the magnet field collapses and the EMF is coupled over to the secondary windings, as well as the
drive windings. The drive windings at pin (

) produce a run voltage pulse which is rectified by

D907

, filtered by

C911

then clamped by

D911

and now becomes run voltage (

23.3V

) for

I901

The RED LED

D912