Feedback Circuit - Sony D98 chassis Operation Manual

From D601
Q602
D603
R609
R608
R606 C615
From D601
R613
9
and video circuits. The +16.5 volt and the 8-volt lines supply the input voltages for +12V and +5V regulator sections, respect-
fully. During active off or suspend mode a standby back up circuit supplies the 16.5-volt line to the +5 volt section.
+5V Standby Circuit
Normally, the +8V line supplies the +5V regulator. During active off or suspend modes, the voltage supplying the +5 regulator,
IC605, will become very low. In order to prevent loss of the +5V, it is necessary to supply a back up voltage. Supplying +16.5V
line to the regulator through Q601 does this. Note: at this time the +16.5V has been reduced to 8.7 volts.
In Active off mode, Q607 is off, Q606 is on and Q601 is on. Through Q601, IC605 receives its input voltage for +5V. In Active
On mode, Q607 is on, Q606 is off and Q601 is off. Since Q601 is off, IC605 must receive the +8 volt line through D610.
There is a time delay in this circuit, which is used to insure that during any transitions, the +5V line does not drop out. These
components are C636, R638 and D619.
Heater Voltage Regulator
Heater filament voltage is supplied by the 8-volt line and is regulated by IC604. Heater on/off is used to turn the output on or off.
This is found at pin 4, VC. The output is off during active off and suspend modes.

Feedback Circuit

The feed back circuit is divided into two sections. One is for active off and suspend modes, the other for active on mode.
The following two sections explains the theory and operation.
Active Off and Suspend Mode Feedback
Feedback is provided by circuit elements IC603, D632, Q658 and Q656. The 16.5V line is regulated and the actual voltage
is 8.7. Due to this condition, B+ is no longer regulated and is reduced approximately 67%.
During active off and suspend modes, remote on/off is low and Q656 is off. Current flows through D632 when the 16.5 V
line is greater than 8.2 volts. This current biases Q658 and current from IC603 is allowed to sink to ground. The 16.5-volt
line supplies this current to IC603. The current through IC603 biases its transistor and sinks current from IC601 pin 9. IC601
then responds accordingly and adjusts its duty cycle in order to make the output voltage reach 8.7 volts. This completes the
feedback loop.
T601
SRT
2
D615
C619
R615
5
D633 7
8
D605
9
C614
D608
7 6 4 2 1
IC601
D656
-16V
D653
18
-16V
D654
17
PROTECTOR To IC604
D655
16
16V
15
16V
D652
D651
14
80V
D650
13
180V
12
To IC502 Pin 3
D649
To HDY-
11
D648
10
To
16V
IC501
Pin5
D631
Q658
5V
IC606
Q605
- -
5
Q657
IC603
SHUTDOWN
3
R660
IC652
1
D632
R663
Q656 2
R659
REMOTE ON/
OFF
180V
PWR
R668
C613