Hitachi 43FWX20B, Тренировка

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DP-2X PROTECT SHUTDOWN CIRCUIT EXPLANATION
PAGE 01-18
Protect Shut Down Circuit Diagram explanation:
(See DP-27 Protect Shut Down Diagram for details)
Use this explanation and Diagram in conjunction with the following diagram,
DP-2X Signal Power Supply (Low Voltage) Shut Down Circuit (PROTECT _DEF)
The following circuits are routed to the Lo Voltage Shut Down Circuit through connection point
(PROTECT _DEF) depicted on the Circuit drawing:
EXCESSIVE HIGH VOLTAGE DETECTION
Whenever the High Voltage fluctuates, every other pin off the flyback will fluctuate as well. In this case, a lower
voltage source can be used to determine the status of the High Voltage.
Pin
5 (50P) is used to monitor for excessive High Voltage. The pulse off the flyback is rectified by DH13 and
filtered by
CH17
. This voltage sets on the cathode of two zener diodes
DH15
and
DH14
.
DH15
is a HZ22V zener. If the voltage at the cathode rises too high, the zener will fire and send a Shut Down
signal through PPD3 pin 6 . This signal is routed to the appropriate circuit on the Lo Voltage Shut Down Circuit.
The Shut Down signal is depicted as PROTECT _DEF .
DH14 is a HZ36V zener. If the voltage at the cathode rises too high, the zener will fire and send a Shut Down
signal through to pin
7
of
IH01
which is the OVP input pin. This high will cause
IH01
to stop producing the Hi
Voltage Drive signal from pin 1 .
EXCESSIVE CURRENT TO THE VERTICAL OUTPUT IC DETECTION
(See Figure 1)
This circuit uses a low ohm resistor R629 in series
with the SW +28V. The value of this resistor
0.68
ohm . When the current demand increases, the volt-
age drop across the resistor increases. If the voltage
drop is sufficient to reduce the voltage on the base of
Q604 , the transistor will conduct, producing a Shut-
down signal through D608 through PPD3 pin 6 . This
signal is routed to the appropriate circuit on the Lo
Voltage Shut Down Circuit. The Shut Down signal
is depicted as
PROTECT _DEF .
SIDE PINCUSHION FAILURE DETECTION
If the side pincushion circuit fails in such a way as to produce an excessive high on the cathode of D702 (a
HZS7C3) the zener will fire producing a Shutdown signal through
D703 through PPD3 pin 6 . This signal is
routed to the appropriate circuit on the Lo Voltage Shut Down Circuit. The Shut Down signal is depicted as
PROTECT _DEF .
-5V LOSS DETECTION
The purpose of the Negative Voltage Loss detection circuit is to compare the
negative voltage with its’ counter part positive voltage. If at any time, the nega-
tive voltage drops or disappears, the circuit will produce a Shutdown signal.
In Figure 2, there are two resistors of equal value. One to the positive voltage
+5V and one to the negative voltage -5V) . At their tie point, (neutral point) , the
voltage is effectually zero (0) volts. If the negative voltage is lost, the neutral
point will go positive. This high is routed through
DK90 through PPD3 pin 6 .
This signal is routed to the appropriate circuit on the Lo Voltage Shut Down Cir-
cuit. The Shut Down signal is depicted as
PROTECT _DEF
.
Current Sensor
Base
Bias
SW +28V
Shut-Down Signal
R629
0.68
Q604
Figure 1
+5V -5V
Shut-Down Signal
Voltage
Loss
Detector
DK90
Figure 2