Hitachi 51F510, Manual

Page: 26 / 152

DP-4X SIGNAL POWER SUPPLY 5.7V REGULATION EXPLANATION
PAGE 01-1
9
5.7V Power Supply Regulation Circuit Diagram explanation:
(See Signal Power Supply 5.7V Regulation Circuit Diagram for details)
THIS POWER SUPPLY RUNS ONLY WHEN THE POWER 1 COMMAND IS ACTIVE HIGH:
TURNING ON THE 5.7V POWER SUPPLY:
( See Power On/Off Circuit Diagram).
RY101 directs AC to the Low Voltage Power Supply.
When the set is turned on, the POWER SIG command is supplied from pin 59 of the Microprocessor I004 . This
high is sent to Q018 and Q021 then to the PPS1 connector pin 9 labeled POWER 1 . From here this high goes
through R110 and then D109 to the Base of Q101 . The base goes high and the transistor turns on. This action
supplies a ground return for the coil inside RY101 and the relay turns on supplying AC through F102 to the Sig-
nal Power Supply rectifier DS201 and the Signal Power Supply begins to operate.
DS201 develops raw 150V which is routed through T201 primary to the Drain of Q201 . From the Source of
Q201 (when switched) the primary of T201 is grounded through a 0.1 low ohm resistors R204 .
As the current draw across R204 rises and falls due to the load, the developed DC Voltage is sent to pin 3 of
IC201 which is the Over Current Detection pin. If this voltage goes too high, the power supply will shut down
until the over voltage condition disappears. Q201 gate control is via pin 5 of IC201 .
After the Signal Power Supply begins to operate,
IC201
needs
Run Voltage
. This is accomplished by the pulse
from T201 which is rectified by D204 , filtered by C206 and the DC component arrives at pin 6 of IC201 .
5.7V REGULATION
5.7V pulse is generated from on the secondary of
T201
. This pulse is rectified by
D210
, filtered by
C228
and
C229 .
The primary route for the 5.7V is through L204 and output as DM 5.6V to the Digital Module.
However, the regulation route is to the cathode of IC203 . This regulator circuit works as a variable resistor
whose resistance is dependant upon the 5.7V voltage fluctuations. This variable resistor manipulates the current
flow from pin 2 of PC201 . Internally, the LED is illuminated by degrees dependant upon the 5.7V voltage fluc-
tuations which causes the resistance of IC203 to fluc
t
uate. The internal receiver receives this light and acts as a
variable resistor from pin
4
to pin
3
, which is the regulation control signal to pin
2
labeled as
F/B
.
This action causes pin 2 of IC201 to manipulate the internal oscillator within IC201 . This in turn causes the tim-
ing of the drive pulses delivered to the Gate of Q201 SMOSFET (Switch Metal Oxide Semiconductor Field Ef-
fect Transistor) to manipulate the frequency of the pulse generated on the primary of T201 . The current drain of
these SMOSFETs is monitored by the low ohm resistor R204 mentioned above. If this current exceeds a specific
value, the voltage developed by this low ohm resistor is routed through R213 back into pin 3 of IC201 which is
the Over Current Protection circuit. This pin will inhibit the drive signal to the gate of the SMOSFETs. As soon
as the excessive current situation is eliminated, the IC will recover and continue functioning.
B+ GENERATION FOR THE POWER SUPPLY DRIVER IC201:
Vcc for the Driver IC is first generated by the AC input. This voltage is called Start Up Voltage . IC201 requires
23.3V DC to operate normal. However, it will begin operation at a much smaller voltage on pin 6 .
When AC is applied to the main full wave bridge rectifier DS201 where it is converted to Raw 150V DC voltage,
filtered by C201 and C202 , routed through R202 , R203 and R210 and made available to pin 6 of IC201 as start
up voltage. When this voltage reaches 12Vdc, the internal Regulator of
IC201
is turned On and begins operation.
When the power supply begins to operate, the magnet field collapses and the EMF is coupled over to the secon-
dary windings, as well as the drive windings. One drive winding produces a run voltage pulse which is rectified
by
D204 , filtered by C206 and becomes run voltage ( 23.3V ) for IC201 pin 6 .