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DP-4X GENERIC POWER SUPPLY SHUTDOWN EXPLANATION
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.
SW+115V
Current Sensor
CP46
QP05
Figure 1
Negative
Voltage Loss
Detector
RK23
2.7K
SW +5V
DP39
RP38
RP39
DP38
Figure 3
RP34
0.39
RP35
Base
Bias
RP36
Shutdown Signal
Shutdown Signal
DK18
RK22
1.8K
SW -5V
Figure 2
SW +115V
Voltage Too
High Detector
Shutdown
Signal
(Continued on page 6)
PAGE 01-01
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