Hitachi 51F510, Manual

Page: 7 / 152

DP-4X GENERIC POWER SUPPLY SHUTDOWN EXPLANATION
PAGE 01-01
GENERIC SHUTDOWN CIRCUITS EXPLAINED:
The following circuits are commonly used in Hitachi product and relate to the drawings for Shutdown:
SW +115V EXCESSIVE CURRENT DETECTION
(See Figure 1)
One very common circuit used in many Hitachi tele-
vision products is the B+
Excessive Current Sens-
ing circuit. In this circuit is a low ohm resistor RP34
in series with the SW +115V. The value of this resis-
tor is
0.39 ohm . When the current demand in-
creases, the voltage drop across the resistor in-
creases. If the voltage drop is sufficient to reduce the
voltage on the base of
QP05 , the transistor will con-
duct, producing a Shutdown signal that is directed to
the appropriate circuits indicated on the drawing for
Deflection Power Supply Shutdown Output Circuit,
OCP & OVP.
NEGATIVE VOLTAGE LOSS DETECTION
(See Figure 2)
The purpose of the Negative Voltage Loss detection circuit is to
compare the negative voltage with its counter part positive volt-
age. If at any time, the negative voltage drops or disappears, the
circuit will produce a Shutdown signal.
In Figure 2, there are two resistors. 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, actually
about 1 Volt negative. If however, the negative voltage is lost,
the neutral point will go positive. This in turn will create a Shut-
down Signal through
DK18 and on to the appropriate circuit in-
dicated on the drawing for Deflection Power Supply Shutdown
Output Circuit, OCP & OVP.
VOLTAGE TOO HIGH DETECTION
( See Figure 3)
Another circuit used is the Voltage Too High Detec-
tion circuit. In the example shown in Figure 3, the
zener diode DP39 is connected to a voltage divider
RP38 and RP39 . If the voltage source rises too high,
the voltage at the divider center point will rise as well
and trigger or fire the zener diode which produces a
Shutdown signal through
DP38 and on to the appro-
priate circuit indicated on the drawing for Deflection
Power Supply Shutdown Output Circuit, OCP & OVP.
Figure 1
SW +5V
Shutdown Signal
DK18
SW -5V
RK23
2.7K
RK22
1.8K
Negative
Voltage Loss
Detector
Figure 2
SW +115V
Voltage Too
High Detector
Shutdown
Signal
DP39
DP38
RP38
RP39
Figure 3
(Continued on page 6)
Current Sensor
Base
Bias
Shutdown Signal
RP34
0.39
QP05
SW+115V
CP46
RP36
RP35